目录:
关键词:GIC、IAR、EOI、SGI/PPI/SPI、中断映射、中断异常向量、中断上下文、内核中断线程、中断注册。
由于篇幅较大,简单梳理一下内容。
本章主要可以分为三大部分:
讲解硬件背景的1. ARM中断控制器。
系统初始化的静态过程:GIC初始化和各中断的中断号映射2. 硬件中断号和Linux中断号的映射;每个中断的注册5. 注册中断。
一个中断从产生到执行完毕的动态过程:ARM底层通用部分如何处理3. ARM底层中断处理;GIC部分的处理流程以及上层通用处理部分4. 高层中断处理。
这里的高层处理,没有包括下半部。下半部在Linux中断管理 (2)软中断和tasklet和Linux中断管理 (3)workqueue工作队列中进行介绍。
1. ARM中断控制器
1.1 ARM支持中断类型
ARM GIC-v2支持三种类型的中断:
SGI:软件触发中断(Software Generated Interrupt),通常用于多核间通讯,最多支持16个SGI中断,硬件中断号从ID0~ID15。SGI通常在Linux内核中被用作IPI中断(inter-processor interrupts),并会送达到系统指定的CPU上。
PPI:私有外设中断(Private Peripheral Interrupt),是每个CPU私有的中断。最多支持16个PPI中断,硬件中断号从ID16~ID31。PPI通常会送达到指定的CPU上,应用场景有CPU本地时钟。
SPI:公用外设中断(Shared Peripheral Interrupt),最多可以支持988个外设中断,硬件中断号从ID32~ID1019。
1.2 GIC检测中断流程
GIC主要由两部分组成,分别是仲裁单元(Distributor)和CPU接口模块。
GIC仲裁单元为每一个中断维护一个状态机,分别是:inactive、pending、active and pending、active。
下面是来自IHI0048B GIC-V2规格书3.2.4 Interrupt handling state machine截图:
GIC检测中断流程如下:
(1) 当GIC检测到一个中断发生时,会将该中断标记为pending状态(A1)。
(2) 对处于pending状态的中断,仲裁单元回确定目标CPU,将中断请求发送到这个CPU上。
(3) 对于每个CPU,仲裁单元会从众多pending状态的中断中选择一个优先级最高的中断,发送到目标CPU的CPU Interface模块上。
(4) CPU Interface会决定这个中断是否可以发送给CPU。如果该终端优先级满足要求,GIC会发生一个中断信号给该CPU。
(5) 当一个CPU进入中断异常后,会去读取GICC_IAR寄存器来响应该中断(一般是Linux内核的中断处理程序来读寄存器)。寄存器会返回硬件中断号(hardware interrupt ID),对于SGI中断来说是返回源CPU的ID。
当GIC感知到软件读取了该寄存器后,又分为如下情况:
* 如果该中断源是pending状态,那么转改将变成active。(C)
* 如果该中断又重新产生,那么pending状态变成active and pending。(D)
* 如果该中断是active状态,现在变成active and pending。(A2)
(6) 当处理器完成中断服务,必须发送一个完成信号EOI(End Of Interrupt)给GIC控制器。软件写GICC_EOIR寄存器,状态变成inactive。(E1)
补充:
(7) 对于level triggered类型中断来说,当触发电平消失,状态从active and pending变成active。(B2)
常用路径是A1->D->B2->E1。
1.2.1 GIC中断抢占
GIC中断控制器支持中断优先级抢占,一个高优先级中断可以抢占一个低优先级且处于active状态的中断,即GIC仲裁单元会记录和比较当前优先级最高的pending状态,然后去抢占当前中断,并且发送这个最高优先级的中断请求给CPU,CPU应答了高优先级中断,暂停低优先级中断服务,进而去处理高优先级中断。
GIC会将pending状态优先级最高的中断请求发送给CPU。
1.2.2 Linux对中断抢占处理
从GIC角度看,GIC会发送高优先级中断请求给CPU。
但是目前CPU处于关中断状态,需要等低优先级中断处理完毕,直到发送EOI给GIC。
然后CPU才会响应pending状态中优先级最高的中断进行处理。
所以Linux下:
1. 高优先级中断无法抢占正在执行的低优先级中断。
2.同处于pending状态的中断,优先响应高优先级中断进行处理。
1.3 GIC中断时序
借助GIC-400 Figure B-2 Signaling physical interrupts理解GIC内部工作原理。
M和N都是SPI类型的外设中断,且通过FIQ来处理,高电平触发,N的优先级比M高,他们的目标CPU相同。
(1) T1时刻:GIC的总裁单元检测到中断M的电平变化。
(2) T2时刻:仲裁单元设置中断M的状态为pending。
(3) T17时刻:CPU Interface模块会拉低nFIQCPU[n]信号。在中断M的状态变成pending后,大概需要15个时钟周期后会拉低nFIQCPU[n]信号来向CPU报告中断请求(assertion)。仲裁单元需要这些时间来计算哪个是pending状态下优先级最高的中断。
(4) T42时刻:仲裁单元检测到另外一个优先级更高的中断N。
(5) T43时刻:仲裁单元用中断N替换中断M为当前pending状态下优先级最高的中断,并设置中断N为pending状态。
(6) T58时刻:经过tph个时钟后,CPU Interface拉低你FIOCPU[n]信号来通知CPU。因为此信号在T17时刻已经被拉低,CPU Interface模块会更新GICC_IAR寄存器的Interrupt ID域,该域的值变成中断N的硬件中断号。
(7) T61~T131时刻:Linux对中断N的服务程序--------------------------------------------------------------中断服务程序处理段,从GICC_IAR开始到GICC_EOIR结束。
T61时刻:CPU(Linux中断服务例程)读取GICC_IAR寄存器,即软件响应了中断N。这时仲裁单元把中断N的状态从pending变成active and pending。读取GICC_IAR
T64时刻:在中断N被Linux相应3个时钟内,CPU Interface模块完成对nFIQCPU[n]信号的deasserts,即拉高nFIQCPU[n]信号。
T126时刻:外设也deassert了该中断N。
T128时刻:仲裁单元移出了中断N的pending状态。
T131时刻:Linux服务程序把中断N的硬件ID号写入GICC_EOIR寄存器来完成中断N的全部处理过程。写GICC_EOIR
(8) T146时刻:在向GICC_EOIR寄存器写入中断N中断号后的tph个时钟后,仲裁单元会选择下一个最高优先级中断,即中断M,发送中断请求给CPU Interface模块。CPU Interface会拉低nFIQCPU[n]信号来向CPU报告外设M的中断请求。
(9) T211时刻:Linux中断服务程序读取GICC_IAR寄存器来响应中断,仲裁单元设置中断M的状态为active and pending。
(10) T214时刻:在CPU响应中断后的3个时钟内,CPU Interface模块拉高nFIOCPU[n]信号来完成deassert动作。
那么GICC_IAR和GICC_EOIR分别在Linux什么地方触发的呢?
1.4 Cortex A15 A7实例
2. 硬件中断号和Linux中断号的映射
2.1 硬件中断号:一个串口中断实例
2.2 中断控制器初始化
DTS中GIC定义于arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts:
gic: interrupt-controller@2c001000 { compatible = "arm,cortex-a15-gic", "arm,cortex-a9-gic";------------------此设备的标识符是"arm,cortex-a15-gic" #interrupt-cells = <3>; #address-cells = <0>; interrupt-controller;----------------------------------------------------表示此设备是一个中断控制器 reg = <0 0x2c001000 0 0x1000>, <0 0x2c002000 0 0x1000>, <0 0x2c004000 0 0x2000>, <0 0x2c006000 0 0x2000>; interrupts = <1 9 0xf04>; };
struct irq_domain用于描述一个中断控制器。
GIC中断控制器在初始化时解析DTS信息中定义了几个GIC控制器,每个GIC控制器注册一个struct irq_domain数据结构。
struct irq_domain { struct list_head link;-------------------------用于将irq_domain连接到全局链表irq_domain_list中。 const char *name;------------------------------中断控制器名称 const struct irq_domain_ops *ops;--------------irq domain映射操作使用的方法集合 void *host_data; unsigned int flags; /* Optional data */ struct device_node *of_node;------------------对应中断控制器的device node struct irq_domain_chip_generic *gc; #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY struct irq_domain *parent; #endif /* reverse map data. The linear map gets appended to the irq_domain */ irq_hw_number_t hwirq_max;--------------------该irq domain支持中断数量的最大值。 unsigned int revmap_direct_max_irq; unsigned int revmap_size;---------------------线性映射的大小 struct radix_tree_root revmap_tree;-----------Radix Tree映射的根节点 unsigned int linear_revmap[];-----------------线性映射用到的lookup table }
struct irq_domain_ops定义了irq_domain方法集合,xlate从intspec中解析出硬件中断号和中断类型,intspec[0]和intspec[1]决定中断号,intspec[2]决定中断类型。
struct irq_domain_ops { int (*match)(struct irq_domain *d, struct device_node *node); int (*map)(struct irq_domain *d, unsigned int virq, irq_hw_number_t hw); void (*unmap)(struct irq_domain *d, unsigned int virq); int (*xlate)(struct irq_domain *d, struct device_node *node, const u32 *intspec, unsigned int intsize, unsigned long *out_hwirq, unsigned int *out_type); #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY /* extended V2 interfaces to support hierarchy irq_domains */ int (*alloc)(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs, void *arg); void (*free)(struct irq_domain *d, unsigned int virq, unsigned int nr_irqs); void (*activate)(struct irq_domain *d, struct irq_data *irq_data); void (*deactivate)(struct irq_domain *d, struct irq_data *irq_data); #endif }; static const struct irq_domain_ops gic_irq_domain_hierarchy_ops = { .xlate = gic_irq_domain_xlate, .alloc = gic_irq_domain_alloc, .free = irq_domain_free_irqs_top, }; static int gic_irq_domain_xlate(struct irq_domain *d, struct device_node *controller, const u32 *intspec, unsigned int intsize, unsigned long *out_hwirq, unsigned int *out_type) { ... /* Get the interrupt number and add 16 to skip over SGIs */ *out_hwirq = intspec[1] + 16;--------------------------------------首先+16跳过SGI类型中断 /* For SPIs, we need to add 16 more to get the GIC irq ID number */ if (!intspec[0]) {-------------------------------------------------如果是SPI类型中断,还需要+16,跳过PPI类型中断。 ret = gic_routable_irq_domain_ops->xlate(d, controller, intspec, intsize, out_hwirq, out_type); if (IS_ERR_VALUE(ret)) return ret; } *out_type = intspec[2] & IRQ_TYPE_SENSE_MASK;---------------------中断触发类型,包括四种上升沿、下降沿、高电平、低电平。 return ret; } static int gic_irq_domain_alloc(struct irq_domain *domain, unsigned int virq, unsigned int nr_irqs, void *arg) { int i, ret; irq_hw_number_t hwirq; unsigned int type = IRQ_TYPE_NONE; struct of_phandle_args *irq_data = arg; ret = gic_irq_domain_xlate(domain, irq_data->np, irq_data->args, irq_data->args_count, &hwirq, &type);---------------首先根据args翻译出硬件中断号和中断类型。 if (ret) return ret; for (i = 0; i < nr_irqs; i++) gic_irq_domain_map(domain, virq + i, hwirq + i);---------------执行软硬件的映射,并且根据中断类型设置struct irq_desc->handle_irq处理函数。 return 0; } void irq_domain_free_irqs_top(struct irq_domain *domain, unsigned int virq, unsigned int nr_irqs) { int i; for (i = 0; i < nr_irqs; i++) { irq_set_handler_data(virq + i, NULL); irq_set_handler(virq + i, NULL); } irq_domain_free_irqs_common(domain, virq, nr_irqs); }
针对SPI类型中断,需要进行+16位移。
static int gic_routable_irq_domain_xlate(struct irq_domain *d, struct device_node *controller, const u32 *intspec, unsigned int intsize, unsigned long *out_hwirq, unsigned int *out_type) { *out_hwirq += 16; return 0; }
gic_irq_domain_map()入参有struct irq_domain和软硬件中断号,主要分SGI/PPI一组,SPI一组。
主要工作由irq_domain_set_info()处理,irq_domain_set_hwirq_and_chip()通过Linux中断号获取struct irq_data数据结构,设置关联硬件中断号和struct irq_chip gic_chip关联。
__irq_set_handler()设置中断描述符irq_desc->handler_irq回调函数,对SPI类型来说就是handle_fasteoi_irq()。
static int gic_irq_domain_map(struct irq_domain *d, unsigned int irq, irq_hw_number_t hw) { if (hw < 32) { irq_set_percpu_devid(irq);-------------------------------PerCPU类型的中断有自己的特殊flag。 irq_domain_set_info(d, irq, hw, &gic_chip, d->host_data, handle_percpu_devid_irq, NULL, NULL); set_irq_flags(irq, IRQF_VALID | IRQF_NOAUTOEN); } else { irq_domain_set_info(d, irq, hw, &gic_chip, d->host_data, handle_fasteoi_irq, NULL, NULL); set_irq_flags(irq, IRQF_VALID | IRQF_PROBE); gic_routable_irq_domain_ops->map(d, irq, hw); } return 0; } void irq_domain_set_info(struct irq_domain *domain, unsigned int virq, irq_hw_number_t hwirq, struct irq_chip *chip, void *chip_data, irq_flow_handler_t handler, void *handler_data, const char *handler_name) { irq_domain_set_hwirq_and_chip(domain, virq, hwirq, chip, chip_data); __irq_set_handler(virq, handler, 0, handler_name); irq_set_handler_data(virq, handler_data); } int irq_domain_set_hwirq_and_chip(struct irq_domain *domain, unsigned int virq, irq_hw_number_t hwirq, struct irq_chip *chip, void *chip_data) { struct irq_data *irq_data = irq_domain_get_irq_data(domain, virq); if (!irq_data) return -ENOENT; irq_data->hwirq = hwirq; irq_data->chip = chip ? chip : &no_irq_chip; irq_data->chip_data = chip_data; return 0; } void __irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained, const char *name) { unsigned long flags; struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, 0); ... desc->handle_irq = handle;--------------------irq_desc->handler_irq和name赋值。 desc->name = name; ... }
drivers/irqchip/irq-gic.c定义了"arm,cortex-a15-gic"的处理函数gic_of_init,gic_of_init是GIC控制器的初始化函数。
IRQCHIP_DECLARE(cortex_a15_gic, "arm,cortex-a15-gic", gic_of_init); static int gic_cnt __initdata; static int __init gic_of_init(struct device_node *node, struct device_node *parent) { ... gic_init_bases(gic_cnt, -1, dist_base, cpu_base, percpu_offset, node); if (!gic_cnt) gic_init_physaddr(node); if (parent) { irq = irq_of_parse_and_map(node, 0); gic_cascade_irq(gic_cnt, irq); } if (IS_ENABLED(CONFIG_ARM_GIC_V2M)) gicv2m_of_init(node, gic_data[gic_cnt].domain); gic_cnt++; return 0; }
gic_init_bases的gic_nr是GIC控制器的序号,主要调用irq_domain_add_linear()分配并函数注册一个irq_domain。
void __init gic_init_bases(unsigned int gic_nr, int irq_start, void __iomem *dist_base, void __iomem *cpu_base, u32 percpu_offset, struct device_node *node) { irq_hw_number_t hwirq_base; struct gic_chip_data *gic; int gic_irqs, irq_base, i; int nr_routable_irqs; BUG_ON(gic_nr >= MAX_GIC_NR);---------------------------gic_nr不超过系统规定的MAX_GIC_NR gic = &gic_data[gic_nr];--------------------------------struct gic_chip_data类型的全局变量gic_data,序号是GIC控制器序号 ... /* * Initialize the CPU interface map to all CPUs. * It will be refined as each CPU probes its ID. */ for (i = 0; i < NR_GIC_CPU_IF; i++) gic_cpu_map[i] = 0xff; /* * Find out how many interrupts are supported. * The GIC only supports up to 1020 interrupt sources. */ gic_irqs = readl_relaxed(gic_data_dist_base(gic) + GIC_DIST_CTR) & 0x1f;------------计算GIC控制器最多支持的中断源个数 gic_irqs = (gic_irqs + 1) * 32; if (gic_irqs > 1020)----------------------------------------------------------------GIC支持的最大中断数据,此处为1020 gic_irqs = 1020; gic->gic_irqs = gic_irqs; if (node) { /* DT case */ const struct irq_domain_ops *ops = &gic_irq_domain_hierarchy_ops;--------------GICv2的struct irq_domain_ops ... gic->domain = irq_domain_add_linear(node, gic_irqs, ops, gic);-----------------注册irq_domain,操作函数使用gic_irq_domain_hierarchy_ops } else { /* Non-DT case */ ... } if (WARN_ON(!gic->domain)) return; if (gic_nr == 0) { #ifdef CONFIG_SMP set_smp_cross_call(gic_raise_softirq); register_cpu_notifier(&gic_cpu_notifier); #endif set_handle_irq(gic_handle_irq);-------在irq_handler中调用handle_arch_irq,这里将handle_arch_irq指向gic_handle_irq,实现了平台中断和具体GIC中断的关联。 } gic_chip.flags |= gic_arch_extn.flags; gic_dist_init(gic);----------------------GIC Distributer部分初始化 gic_cpu_init(gic);-----------------------GIC CPU Interface部分初始化 gic_pm_init(gic);------------------------GIC PM相关初始化 }
irq_domain_add_linear()->__irq_domain_add()分配并初始化struct irq_domain。
struct irq_domain *__irq_domain_add(struct device_node *of_node, int size, irq_hw_number_t hwirq_max, int direct_max, const struct irq_domain_ops *ops, void *host_data) { struct irq_domain *domain; domain = kzalloc_node(sizeof(*domain) + (sizeof(unsigned int) * size), GFP_KERNEL, of_node_to_nid(of_node));-------------domain大小为struct irq_domain加上gic_irqs个unsigned int。 if (WARN_ON(!domain)) return NULL; /* Fill structure */ INIT_RADIX_TREE(&domain->revmap_tree, GFP_KERNEL); domain->ops = ops; domain->host_data = host_data; domain->of_node = of_node_get(of_node); domain->hwirq_max = hwirq_max; domain->revmap_size = size; domain->revmap_direct_max_irq = direct_max; irq_domain_check_hierarchy(domain); mutex_lock(&irq_domain_mutex); list_add(&domain->link, &irq_domain_list);----------------------将创建好的struct irq_domain加入全局链表irq_domain_list。 mutex_unlock(&irq_domain_mutex); pr_debug("Added domain %s\n", domain->name); return domain; }
2.3 系统初始化之中断号映射
上一小节是中断控制器GIC的初始化,下面看看一个硬件中断是如何映射到Linux空间的中断的。
customize_machine()是arch_initcall阶段调用,很靠前。
customize_machine
->of_platform_populate
->of_platform_bus_create
->of_amba_device_create
下面结合dtsi文件看看来龙去脉,arch/arm/boot/dts/vexpress-v2m.dtsi。
/dts-v1/; / { model = "V2P-CA9"; arm,hbi = <0x191>; arm,vexpress,site = <0xf>; compatible = "arm,vexpress,v2p-ca9", "arm,vexpress"; interrupt-parent = <&gic>; #address-cells = <1>; #size-cells = <1>; ... gic: interrupt-controller@1e001000 { compatible = "arm,cortex-a9-gic"; #interrupt-cells = <3>; #address-cells = <0>; interrupt-controller; reg = <0x1e001000 0x1000>, <0x1e000100 0x100>; }; ... smb { compatible = "simple-bus"; #address-cells = <2>; #size-cells = <1>; ranges = <0 0 0x40000000 0x04000000>, <1 0 0x44000000 0x04000000>, <2 0 0x48000000 0x04000000>, <3 0 0x4c000000 0x04000000>, <7 0 0x10000000 0x00020000>; #interrupt-cells = <1>; interrupt-map-mask = <0 0 63>; interrupt-map = <0 0 0 &gic 0 0 4>, <0 0 1 &gic 0 1 4>, ... /include/ "vexpress-v2m.dtsi" }; } vexpress-v2m.dtsi文件: motherboard { model = "V2M-P1"; arm,hbi = <0x190>; arm,vexpress,site = <0>; compatible = "arm,vexpress,v2m-p1", "simple-bus"; #address-cells = <2>; /* SMB chipselect number and offset */ #size-cells = <1>; #interrupt-cells = <1>; ranges; ... iofpga@7,00000000 { compatible = "arm,amba-bus", "simple-bus"; #address-cells = <1>; #size-cells = <1>; ranges = <0 7 0 0x20000>; ... v2m_serial0: uart@09000 { compatible = "arm,pl011", "arm,primecell"; reg = <0x09000 0x1000>; interrupts = <5>; clocks = <&v2m_oscclk2>, <&smbclk>; clock-names = "uartclk", "apb_pclk"; }; ... }; }
这里首先从根目录下查找"simple-bus",从上面可以看出指向smb设备。
smb设备包含vexpress-v2m.dtsi文件,然后在of_platform_bus_create()中遍历所有设备。
const struct of_device_id of_default_bus_match_table[] = { { .compatible = "simple-bus", }, #ifdef CONFIG_ARM_AMBA { .compatible = "arm,amba-bus", }, #endif /* CONFIG_ARM_AMBA */ {} /* Empty terminated list */ }; static int __init customize_machine(void) { ... of_platform_populate(NULL, of_default_bus_match_table,-----------------找到匹配"simple-bus"的设备,这里指向smb。 NULL, NULL); ... } int of_platform_populate(struct device_node *root, const struct of_device_id *matches, const struct of_dev_auxdata *lookup, struct device *parent) { ... for_each_child_of_node(root, child) { rc = of_platform_bus_create(child, matches, lookup, parent, true);-----这里的root指向根目录,即"/"。 if (rc) break; } ... } static int of_platform_bus_create(struct device_node *bus, const struct of_device_id *matches, const struct of_dev_auxdata *lookup, struct device *parent, bool strict) { const struct of_dev_auxdata *auxdata; struct device_node *child; struct platform_device *dev; const char *bus_id = NULL; void *platform_data = NULL; int rc = 0; /* Make sure it has a compatible property */ if (strict && (!of_get_property(bus, "compatible", NULL))) { pr_debug("%s() - skipping %s, no compatible prop\n", __func__, bus->full_name); return 0; } auxdata = of_dev_lookup(lookup, bus); if (auxdata) { bus_id = auxdata->name; platform_data = auxdata->platform_data; } if (of_device_is_compatible(bus, "arm,primecell")) {------当遇到匹配"arm,primecell"设备,创建amba设备。在ofpga@7,00000000中创建uart@09000设备。 /* * Don't return an error here to keep compatibility with older * device tree files. */ of_amba_device_create(bus, bus_id, platform_data, parent); return 0; } dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent); if (!dev || !of_match_node(matches, bus)) return 0; for_each_child_of_node(bus, child) {----------------遍历smb下的所有"simple-bus"设备,这里可以嵌套几层。从smb->motherboard->iofpga@7,00000000。 pr_debug(" create child: %s\n", child->full_name); rc = of_platform_bus_create(child, matches, lookup, &dev->dev, strict); if (rc) { of_node_put(child); break; } } of_node_set_flag(bus, OF_POPULATED_BUS); return rc; }
of_amba_device_create创建ARM AMBA类型设备,其中中断部分交给irq_of_parse_and_map()处理。
static struct amba_device *of_amba_device_create(struct device_node *node, const char *bus_id, void *platform_data, struct device *parent) { ... /* Decode the IRQs and address ranges */ for (i = 0; i < AMBA_NR_IRQS; i++) dev->irq[i] = irq_of_parse_and_map(node, i); ... }
以uart@09000为例,irq_of_parse_and_map中的of_irq_parse_one()解析设备中的"interrupts"、"regs"等参数,参数放入struct of_phandle_args中,oirq->args[1]中存放中断号5,oirq->np存放struct device_node。
irq_create_of_mapping()建立硬件中断号到Linux中断号的映射。
irq_create_of_mapping主要调用如下,主要工作交给__irq_domain_alloc_irqs()进行处理。
->domain->ops->xlate---------------------------------
->irq_find_mapping
->irq_domain_alloc_irqs
->__irq_domain_alloc_irqs
->irq_domain_alloc_descs
->irq_domain_alloc_irq_data
->irq_domain_alloc_irqs_recursive
->gic_irq_domain_alloc
->gic_irq_domain_map-----------------------进行硬件中断号和软件中断号的映射
->gic_irq_domain_set_info----------------设置重要参数到中断描述符中
->irq_domain_insert_irq
unsigned int irq_of_parse_and_map(struct device_node *dev, int index) { struct of_phandle_args oirq; if (of_irq_parse_one(dev, index, &oirq)) return 0; return irq_create_of_mapping(&oirq); } unsigned int irq_create_of_mapping(struct of_phandle_args *irq_data) { struct irq_domain *domain; irq_hw_number_t hwirq; unsigned int type = IRQ_TYPE_NONE; int virq; domain = irq_data->np ? irq_find_host(irq_data->np) : irq_default_domain;---找到设备所属的struct irq_domain结构体。 ... /* If domain has no translation, then we assume interrupt line */ if (domain->ops->xlate == NULL) hwirq = irq_data->args[0]; else { if (domain->ops->xlate(domain, irq_data->np, irq_data->args,-------调用gic_irq_domain_xlate()函数进行硬件中断号到Linux中断号的转换。 irq_data->args_count, &hwirq, &type)) return 0; } if (irq_domain_is_hierarchy(domain)) {-------------------------可以分层挂载 /* * If we've already configured this interrupt, * don't do it again, or hell will break loose. */ virq = irq_find_mapping(domain, hwirq);-------------------从已有的linear_revmap中寻找Linux中断号。 if (virq) return virq; virq = irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, irq_data);---------如果没有找到,重新分配中断映射。参数1表示每次只分配一个中断。 if (virq <= 0) return 0; } else { ... } /* Set type if specified and different than the current one */ if (type != IRQ_TYPE_NONE && type != irq_get_trigger_type(virq)) irq_set_irq_type(virq, type);-----------------------------设置中断触发类型 return virq; }
struct irq_desc定义了中断描述符,irq_desc[]数组定义了NR_IRQS个中断描述符,数组下标表示IRQ中断号,通过IRQ中断号可以找到对应中断描述符。
struct irq_desc内置了struct irq_data结构体,struct irq_data的irq和hwirq分别对应软件中断号和硬件中断号。通过这两个成员,可以将硬件中断号和软件中断号映射起来。
struct irq_chip定义了中断控制器底层操作相关的方法集合。
struct irq_desc { struct irq_data irq_data; unsigned int __percpu *kstat_irqs; irq_flow_handler_t handle_irq;-----------------根据中断号分类,不同类型中断的处理handle。0~31对应handle_percpu_devid_irq;32~对应handle_fasteoi_irq。 #ifdef CONFIG_IRQ_PREFLOW_FASTEOI irq_preflow_handler_t preflow_handler; #endif struct irqaction *action; /* IRQ action list */ unsigned int status_use_accessors; unsigned int core_internal_state__do_not_mess_with_it; unsigned int depth; /* nested irq disables */ unsigned int wake_depth; /* nested wake enables */ unsigned int irq_count; /* For detecting broken IRQs */ unsigned long last_unhandled; /* Aging timer for unhandled count */ unsigned int irqs_unhandled; atomic_t threads_handled; int threads_handled_last; raw_spinlock_t lock; struct cpumask *percpu_enabled; #ifdef CONFIG_SMP const struct cpumask *affinity_hint; struct irq_affinity_notify *affinity_notify; #ifdef CONFIG_GENERIC_PENDING_IRQ cpumask_var_t pending_mask; #endif #endif unsigned long threads_oneshot;-------------是一个位图,每个比特位代表正在处理的共享oneshot类型中断的中断线程。 atomic_t threads_active;-------------------表示正在运行的中断线程个数 wait_queue_head_t wait_for_threads; #ifdef CONFIG_PM_SLEEP unsigned int nr_actions; unsigned int no_suspend_depth; unsigned int cond_suspend_depth; unsigned int force_resume_depth; #endif #ifdef CONFIG_PROC_FS struct proc_dir_entry *dir; #endif int parent_irq; struct module *owner; const char *name; } struct irq_data { u32 mask; unsigned int irq;-----------------Linux软件中断号 unsigned long hwirq;--------------硬件中断号 unsigned int node; unsigned int state_use_accessors; struct irq_chip *chip; struct irq_domain *domain; #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY struct irq_data *parent_data; #endif void *handler_data; void *chip_data; struct msi_desc *msi_desc; cpumask_var_t affinity; } struct irq_chip { const char *name; unsigned int (*irq_startup)(struct irq_data *data);-------------初始化中断 void (*irq_shutdown)(struct irq_data *data);----------------结束中断 void (*irq_enable)(struct irq_data *data);------------------使能中断 void (*irq_disable)(struct irq_data *data);-----------------关闭中断 void (*irq_ack)(struct irq_data *data);---------------------应答中断 void (*irq_mask)(struct irq_data *data);--------------------屏蔽中断 void (*irq_mask_ack)(struct irq_data *data);----------------应答并屏蔽中断 void (*irq_unmask)(struct irq_data *data);------------------解除中断屏蔽 void (*irq_eoi)(struct irq_data *data);---------------------发送EOI信号,表示硬件中断处理已经完成。 int (*irq_set_affinity)(struct irq_data *data, const struct cpumask *dest, bool force);--------绑定中断到某个CPU int (*irq_retrigger)(struct irq_data *data);----------------重新发送中断到CPU int (*irq_set_type)(struct irq_data *data, unsigned int flow_type);----------------------------设置触发类型 int (*irq_set_wake)(struct irq_data *data, unsigned int on);-----------------------------------使能/关闭中断在电源管理中的唤醒功能。 void (*irq_bus_lock)(struct irq_data *data); void (*irq_bus_sync_unlock)(struct irq_data *data); void (*irq_cpu_online)(struct irq_data *data); void (*irq_cpu_offline)(struct irq_data *data); void (*irq_suspend)(struct irq_data *data); void (*irq_resume)(struct irq_data *data); void (*irq_pm_shutdown)(struct irq_data *data); ... unsigned long flags; }
gic_chip是特定中断控制器的硬件操作函数集,对于GICv2有屏蔽/去屏蔽、EOI、设置中断触发类型、以及设置或者当前芯片状态。
static const struct irq_chip gic_chip = { .irq_mask = gic_mask_irq, .irq_unmask = gic_unmask_irq, .irq_eoi = gic_eoi_irq, .irq_set_type = gic_set_type, .irq_get_irqchip_state = gic_irq_get_irqchip_state, .irq_set_irqchip_state = gic_irq_set_irqchip_state, .flags = IRQCHIP_SET_TYPE_MASKED | IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MASK_ON_SUSPEND, }; static void gic_mask_irq(struct irq_data *d) { gic_poke_irq(d, GIC_DIST_ENABLE_CLEAR); } static void gic_unmask_irq(struct irq_data *d) { gic_poke_irq(d, GIC_DIST_ENABLE_SET); } static void gic_eoi_irq(struct irq_data *d) { writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI); } static int gic_set_type(struct irq_data *d, unsigned int type) { void __iomem *base = gic_dist_base(d); unsigned int gicirq = gic_irq(d); /* Interrupt configuration for SGIs can't be changed */ if (gicirq < 16) return -EINVAL; /* SPIs have restrictions on the supported types */ if (gicirq >= 32 && type != IRQ_TYPE_LEVEL_HIGH && type != IRQ_TYPE_EDGE_RISING) return -EINVAL; return gic_configure_irq(gicirq, type, base, NULL); } static int gic_irq_set_irqchip_state(struct irq_data *d, enum irqchip_irq_state which, bool val) { u32 reg; switch (which) { case IRQCHIP_STATE_PENDING: reg = val ? GIC_DIST_PENDING_SET : GIC_DIST_PENDING_CLEAR; break; case IRQCHIP_STATE_ACTIVE: reg = val ? GIC_DIST_ACTIVE_SET : GIC_DIST_ACTIVE_CLEAR; break; case IRQCHIP_STATE_MASKED: reg = val ? GIC_DIST_ENABLE_CLEAR : GIC_DIST_ENABLE_SET; break; default: return -EINVAL; } gic_poke_irq(d, reg); return 0; } static int gic_irq_get_irqchip_state(struct irq_data *d, enum irqchip_irq_state which, bool *val) { switch (which) { case IRQCHIP_STATE_PENDING: *val = gic_peek_irq(d, GIC_DIST_PENDING_SET); break; case IRQCHIP_STATE_ACTIVE: *val = gic_peek_irq(d, GIC_DIST_ACTIVE_SET); break; case IRQCHIP_STATE_MASKED: *val = !gic_peek_irq(d, GIC_DIST_ENABLE_SET); break; default: return -EINVAL; } return 0; }
irq_domain_alloc_irqs()调用__irq_domain_alloc_irqs()进行struct irq_desc、struct irq_data以及中断映射的处理。
这里的参数nr_irqs一般为1,每次只处理一个中断。
irq_domain_alloc_descs()->irq_alloc_descs()->__irq_alloc_descs()进行struct irq_desc的分配,返回的参数是Linux中断号。
int __irq_domain_alloc_irqs(struct irq_domain *domain, int irq_base, unsigned int nr_irqs, int node, void *arg, bool realloc) { ... if (realloc && irq_base >= 0) { virq = irq_base; } else { virq = irq_domain_alloc_descs(irq_base, nr_irqs, 0, node);-------从allocated_irqs位图中查找第一个nr_irqs个空闲的比特位,最终调用__irq_alloc_descs。 if (virq < 0) { pr_debug("cannot allocate IRQ(base %d, count %d)\n", irq_base, nr_irqs); return virq; } } if (irq_domain_alloc_irq_data(domain, virq, nr_irqs)) {--------------分配struct irq_data数据结构。 pr_debug("cannot allocate memory for IRQ%d\n", virq); ret = -ENOMEM; goto out_free_desc; } mutex_lock(&irq_domain_mutex); ret = irq_domain_alloc_irqs_recursive(domain, virq, nr_irqs, arg);----调用struct irq_domain中的alloc回调函数进行硬件中断号和软件中断号的映射。 if (ret < 0) { mutex_unlock(&irq_domain_mutex); goto out_free_irq_data; } for (i = 0; i < nr_irqs; i++) irq_domain_insert_irq(virq + i); mutex_unlock(&irq_domain_mutex); return virq; ... } int __ref __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node, struct module *owner) { ... mutex_lock(&sparse_irq_lock); start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS, from, cnt, 0);-------------------在allocated_irqs位图中查找第一个连续cnt个为0的比特位区域。 ... bitmap_set(allocated_irqs, start, cnt);-------------bitmap_set()设置这些比特位,表示这些比特位已经被占用。 mutex_unlock(&sparse_irq_lock); return alloc_descs(start, cnt, node, owner);--------这里要看是否定义了CONFIG_SPARSE_IRQ,如果定义了需要动态分配一个struct irq_desc数据结构,以Radix Tree方式存储;没有的话则从irq_desc全局变量中加上偏移即可。 err: mutex_unlock(&sparse_irq_lock); return ret; }
irq_domain_alloc_irqs_recursive()会根据实际情况决定中断控制器的递归处理,
static int irq_domain_alloc_irqs_recursive(struct irq_domain *domain, unsigned int irq_base, unsigned int nr_irqs, void *arg) { int ret = 0; struct irq_domain *parent = domain->parent; bool recursive = irq_domain_is_auto_recursive(domain); BUG_ON(recursive && !parent); if (recursive) ret = irq_domain_alloc_irqs_recursive(parent, irq_base, nr_irqs, arg); if (ret >= 0) ret = domain->ops->alloc(domain, irq_base, nr_irqs, arg); if (ret < 0 && recursive) irq_domain_free_irqs_recursive(parent, irq_base, nr_irqs); return ret; }
至此完成了中断DeviceTree的解析,各数据结构的初始化,以及最主要的硬件中断号到Linux中断号的映射。
3. ARM底层中断处理
ARM底层中断处理的范围是从中断异常触发,到irq_handler。
3.1 中断硬件行为
外设有事件需要报告SoC时,通过和SoC链接的中断管脚发送中断信号,可能是边沿触发信号也可能是电平触发信号。
中断控制器会感知中断信号,中断控制器仲裁单元选择优先级最高的中断发送到CPU Interface,CPU Interface决定将中断分发到哪个CPU核心。
GIC控制器和CPU核心之间通过一个nIRQ(IRQ request input line)信号来通知CPU。
CPU核心感知到中断发生之后,硬件会做如下工作:
- 保存中断发生时CPSR寄存器内容到SPSR_irq寄存器中
- 修改CPSR寄存器,让CPU进入处理器模式(processor mode)中的IRQ模式,即修改CPSR寄存器中的M域设置为IRQ Mode。
- 硬件自动关闭中断IRQ或FIQ,即CPSR中的IRQ位或FIQ位置1。------------硬件自动关中断
- 保存返回地址到LR_irq寄存器中。
- 硬件自动调转到中断向量表的IRQ向量。-------------------------------------------从此处开始进入软件领域
当从中断返回时需要软件实现如下操作:
- 从SPSR_irq寄存器中恢复数据到CPSR中。
- 从LR_irq中恢复内容到PC中,从而返回到中断点的下一个指令处执行。
3.2 中断异常向量
3.2.1 中断异常向量代码段初始化
内核编译时,异常向量表存放在可执行文件的__init段中:arch/arm/kernel/vmlinux.lds.S。
__vectors_start和__vectors_end指向vectors段的开始和结束地址,__stubs_start和__stubs_end存放异常向量stubs代码段。两者都是页面对齐,大小都为一个页面。
__vectors_start = .; .vectors 0 : AT(__vectors_start) { *(.vectors)----------------------------------保存.vectors段数据 } . = __vectors_start + SIZEOF(.vectors); __vectors_end = .; __stubs_start = .; .stubs 0x1000 : AT(__stubs_start) { *(.stubs)------------------------------------存放.stubs段数据 } . = __stubs_start + SIZEOF(.stubs); __stubs_end = .;
系统初始化时会把上述两个段复制到高端地址处,即ixffff_0000:start_kernel->setup_arch->paging_init->devicemap_init。
static void __init devicemaps_init(const struct machine_desc *mdesc) { struct map_desc map; unsigned long addr; void *vectors; /* * Allocate the vector page early. */ vectors = early_alloc(PAGE_SIZE * 2);-------------------------------分配两个页面用于映射到high vectors高端地址。 early_trap_init(vectors);-------------------------------------------实现异常向量表的复制动作。... /* * Create a mapping for the machine vectors at the high-vectors * location (0xffff0000). If we aren't using high-vectors, also * create a mapping at the low-vectors virtual address. */ map.pfn = __phys_to_pfn(virt_to_phys(vectors));---------------------vectors物理页面号 map.virtual = 0xffff0000;-------------------------------------------待映射到的虚拟地址0xffff_0000~0xffff_0fff map.length = PAGE_SIZE;---------------------------------------------映射区间大小 #ifdef CONFIG_KUSER_HELPERS map.type = MT_HIGH_VECTORS;-----------------------------------------映射到high vector #else map.type = MT_LOW_VECTORS; #endif create_mapping(&map); if (!vectors_high()) { map.virtual = 0; map.length = PAGE_SIZE * 2; map.type = MT_LOW_VECTORS; create_mapping(&map); } /* Now create a kernel read-only mapping */ map.pfn += 1; map.virtual = 0xffff0000 + PAGE_SIZE;------------------------------映射到0xffff_1000~0xffff_1ffff map.length = PAGE_SIZE; map.type = MT_LOW_VECTORS; create_mapping(&map); ... }
early_trap_init分别将__vectors_start和__stubs_start两个页面复制到分配的两个页面中。
void __init early_trap_init(void *vectors_base) { ... unsigned long vectors = (unsigned long)vectors_base; extern char __stubs_start[], __stubs_end[]; extern char __vectors_start[], __vectors_end[]; unsigned i; vectors_page = vectors_base; /* * Poison the vectors page with an undefined instruction. This * instruction is chosen to be undefined for both ARM and Thumb * ISAs. The Thumb version is an undefined instruction with a * branch back to the undefined instruction. */ for (i = 0; i < PAGE_SIZE / sizeof(u32); i++) ((u32 *)vectors_base)[i] = 0xe7fddef1;---------------------------第一个页面全部填充未定义指令0xe7fddef1。 /* * Copy the vectors, stubs and kuser helpers (in entry-armv.S) * into the vector page, mapped at 0xffff0000, and ensure these * are visible to the instruction stream. */ memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start); memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start); ... }
3.2.2 中断异常向量
中断发生后,软件跳转到中断向量表开始vector_irq执行,vector_irq在结尾的时候根据中断发生点所在模式,决定跳转到__irq_usr或者__irq_svc。
vector_irq在arch/arm/kernel/entry-armv.S由宏vector_stub定义。
关于correction==4,需要减去4字节才是返回地址?
vector_stub宏参数correction为4,。
正在执行指令A时发生了中断,由于ARM流水线和指令预取等原因,pc指向A+8B处,那么必须等待指令A执行完毕才能处理该中断,这时PC已经更新到A+12B处。
进入中断响应前夕,pc寄存器的内容被装入lr寄存器中,lr=pc-4,即A+8B地址处。
因此返回时要pc=lr-4,才是被中断时要执行的下一条指令。所以lr要回退4B。
.section .vectors, "ax", %progbits__vectors_start: W(b) vector_rst W(b) vector_und W(ldr) pc, __vectors_start + 0x1000 W(b) vector_pabt W(b) vector_dabt W(b) vector_addrexcptn W(b) vector_irq---------------------------------------------------------------跳转到vector_irq W(b) vector_fiq /* * Interrupt dispatcher */ vector_stub irq, IRQ_MODE, 4------------------------------------------------vector_stub宏定义了vector_irq .long __irq_usr @ 0 (USR_26 / USR_32) .long __irq_invalid @ 1 (FIQ_26 / FIQ_32) .long __irq_invalid @ 2 (IRQ_26 / IRQ_32) .long __irq_svc @ 3 (SVC_26 / SVC_32)----------------------------svc模式数值是0b10011,与上0xf后就是3。 .long __irq_invalid @ 4 .long __irq_invalid @ 5 .long __irq_invalid @ 6 .long __irq_invalid @ 7 .long __irq_invalid @ 8 .long __irq_invalid @ 9 .long __irq_invalid @ a .long __irq_invalid @ b .long __irq_invalid @ c .long __irq_invalid @ d .long __irq_invalid @ e .long __irq_invalid @ f
.macro vector_stub, name, mode, correction=0------------------------------------vector_stub宏定义
.align 5
vector_\name: .if \correction sub lr, lr, #\correction-------------------------------------------------------correction==4解释 .endif @ @ Save r0, lr_<exception> (parent PC) and spsr_<exception> @ (parent CPSR) @ stmia sp, {r0, lr} @ save r0, lr mrs lr, spsr str lr, [sp, #8] @ save spsr @ @ Prepare for SVC32 mode. IRQs remain disabled. @ mrs r0, cpsr eor r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)---------------------------------修改CPSR寄存器的控制域为SVC模式,为了使中断处理在SVC模式下执行。 msr spsr_cxsf, r0 @ @ the branch table must immediately follow this code @ and lr, lr, #0x0f--------------------------------------------------------------低4位反映了进入中断前CPU的运行模式,9为USR,3为SVC模式。 THUMB( adr r0, 1f ) THUMB( ldr lr, [r0, lr, lsl #2] )-------------------------------------------根据中断发生点所在的模式,给lr寄存器赋值,__irq_usr或者__irq_svc标签处。 mov r0, spk ARM( ldr lr, [pc, lr, lsl #2] )---------------------------------------------得到的lr就是".long __irq_svc" movs pc, lr @ branch to handler in SVC mode-------------------------把lr的值赋给pc指针,跳转到__irq_usr或者__irq_svc。 ENDPROC(vector_\name)
3.3 内核空间中断处理__irq_svc
__irq_svc处理发生在内核空间的中断,主要svc_entry保护中断现场;irq_handler执行中断处理;如果打开抢占功能,检查是否可以抢占;最后svc_exit执行中断退出处理。
__irq_svc: svc_entry irq_handler #ifdef CONFIG_PREEMPT-----------------------------------------------------中断处理结束后,发生抢占的地方♥ get_thread_info tsk ldr r8, [tsk, #TI_PREEMPT] @ get preempt count--------------获取thread_info->preempt_cpunt变量;preempt_count为0,说明可以抢占进程;preempt_count大于0,表示不能抢占。 ldr r0, [tsk, #TI_FLAGS] @ get flags------------------------获取thread_info->flags变量 teq r8, #0 @ if preempt count != 0 movne r0, #0 @ force flags to 0 tst r0, #_TIF_NEED_RESCHED-----------------------------------------判断是否设置了_TIF_NEED_RESCHED标志位 blne svc_preempt #endif svc_exit r5, irq = 1 @ return from exception UNWIND(.fnend ) ENDPROC(__irq_svc)
svc_entry将中断现场保存到内核栈中,主要是struct pt_regs中的寄存器。
.macro svc_entry, stack_hole=0, trace=1 UNWIND(.fnstart ) UNWIND(.save {r0 - pc} ) sub sp, sp, #(S_FRAME_SIZE + \stack_hole - 4) #ifdef CONFIG_THUMB2_KERNEL SPFIX( str r0, [sp] ) @ temporarily saved SPFIX( mov r0, sp ) SPFIX( tst r0, #4 ) @ test original stack alignment SPFIX( ldr r0, [sp] ) @ restored #else SPFIX( tst sp, #4 ) #endif SPFIX( subeq sp, sp, #4 ) stmia sp, {r1 - r12} ldmia r0, {r3 - r5} add r7, sp, #S_SP - 4 @ here for interlock avoidance mov r6, #-1 @ "" "" "" "" add r2, sp, #(S_FRAME_SIZE + \stack_hole - 4) SPFIX( addeq r2, r2, #4 ) str r3, [sp, #-4]! @ save the "real" r0 copied @ from the exception stack mov r3, lr @ @ We are now ready to fill in the remaining blanks on the stack: @ @ r2 - sp_svc @ r3 - lr_svc @ r4 - lr_<exception>, already fixed up for correct return/restart @ r5 - spsr_<exception> @ r6 - orig_r0 (see pt_regs definition in ptrace.h) @ stmia r7, {r2 - r6} .if \trace #ifdef CONFIG_TRACE_IRQFLAGS bl trace_hardirqs_off #endif .endif .endm
svc_exit准备返回中断现场,然后通过ldmia指令从栈中恢复15个寄存器,包括pc内容,至此整个中断完成并返回。
.macro svc_exit, rpsr, irq = 0... msr spsr_cxsf, \rpsr ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr .endm
irq_handler进入高层中断处理。
4. 高层中断处理
irq_handler汇编宏是ARCH层和高层中断处理分割线,在这里从汇编跳转到C进行GIC相关处理。
前面介绍了一个中断是如何从硬件中断号映射到Linux中断号的,那么当一个中断产生后它从应将到软件识别中断号,再到转换成Linux中断号是什么路径呢?
这里就从irq_handler开始分析流程:
->handle_arch_irq()->gic_handle_irq()
->handle_domain_irq()->__handle_domain_irq()-------------读取IAR寄存器,响应中断,获取硬件中断号
->irq_find_mapping()------------------------------------------------将硬件中断号转变成Linux中断号
->generic_handle_irq()---------------------------------------------之后的操作都是Linux中断号
->handle_percpu_devid_irq()-----------------------------------SGI/PPI类型中断处理
->handle_fasteoi_irq()--------------------------------------------SPI类型中断处理
->handle_irq_event()->handle_irq_event_percpu()------执行中断处理核心函数
->action->handler-----------------------------------------------执行primary handler。
->__irq_wake_thread()----------------------------------------根据需要唤醒中断内核线程
4.1 irq_handler
irq_handler宏调用handle_arch_irq函数,这个函数set_handle_irq注册,GICv2对应gic_handle_irq。
.macro irq_handler #ifdef CONFIG_MULTI_IRQ_HANDLER ldr r1, =handle_arch_irq mov r0, sp adr lr, BSYM(9997f) ldr pc, [r1] #else arch_irq_handler_default #endif 9997: .endm
4.2 gic_handle_irq
git_init_bases设置handle_arch_irq为gic_handle_irq。
void __init gic_init_bases(unsigned int gic_nr, int irq_start, void __iomem *dist_base, void __iomem *cpu_base, u32 percpu_offset, struct device_node *node) { ... if (gic_nr == 0) { ... set_handle_irq(gic_handle_irq); } ... } void __init set_handle_irq(void (*handle_irq)(struct pt_regs *)) { if (handle_arch_irq) return; handle_arch_irq = handle_irq; }
gic_handle_irq对将中断分为两组:SGI、PPI/SPI。
SGI类型中断交给handle_IPI()处理;PPI/SPI类型交给handle_domain_irq处理。
static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) { u32 irqstat, irqnr; struct gic_chip_data *gic = &gic_data[0]; void __iomem *cpu_base = gic_data_cpu_base(gic); do { irqstat = readl_relaxed(cpu_base + GIC_CPU_INTACK);---读取IAR寄存器,表示响应中断。 irqnr = irqstat & GICC_IAR_INT_ID_MASK;-----------------GICC_IAR_INT_ID_MASK为0x3ff,即低10位,所以中断最多从0~1023。 if (likely(irqnr > 15 && irqnr < 1021)) { handle_domain_irq(gic->domain, irqnr, regs); continue; } if (irqnr < 16) {---------------------------------------SGI类型的中断是CPU核间通信所用,只有定义了CONFIG_SMP才有意义。 writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);----直接写EOI寄存器,表示结束中断。 #ifdef CONFIG_SMP handle_IPI(irqnr, regs);----------------------------irqnr表示SGI中断类型 #endif continue; } break; } while (1); }
handle_domain_irq调用__handle_domain_irq,其中lookup置为true。
irq_enter显式告诉Linux内核现在要进入中断上下文了,在处理完中断后调用irq_exit告诉Linux已经完成中断处理过程。
int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq, bool lookup, struct pt_regs *regs) { struct pt_regs *old_regs = set_irq_regs(regs); unsigned int irq = hwirq; int ret = 0; irq_enter();-----------------------------------------------通过显式增加hardirq域计数,通知Linux进入中断上下文 #ifdef CONFIG_IRQ_DOMAIN if (lookup) irq = irq_find_mapping(domain, hwirq);-----------------根据硬件中断号找到对应的软件中断号 #endif /* * Some hardware gives randomly wrong interrupts. Rather * than crashing, do something sensible. */ if (unlikely(!irq || irq >= nr_irqs)) { ack_bad_irq(irq); ret = -EINVAL; } else { generic_handle_irq(irq);--------------------------------开始具体某一个中断的处理,此处irq已经是Linux中断号。 } irq_exit();-------------------------------------------------退出中断上下文 set_irq_regs(old_regs); return ret; }
irq_find_mapping在struct irq_domain中根据hwirq找到Linux环境的irq。
unsigned int irq_find_mapping(struct irq_domain *domain, irq_hw_number_t hwirq) { struct irq_data *data; ... /* Check if the hwirq is in the linear revmap. */ if (hwirq < domain->revmap_size) return domain->linear_revmap[hwirq];----------------linear_revmap[]在__irq_domain_alloc_irqs()->irq_domain_insert_irq()时赋值。 ... }
generic_handle_irq参数是irq号,irq_to_desc()根据irq号找到对应的struct irq_desc。
然后调用irq_desc->handle_irq处理对应的中断。
int generic_handle_irq(unsigned int irq) { struct irq_desc *desc = irq_to_desc(irq); if (!desc) return -EINVAL; generic_handle_irq_desc(irq, desc); return 0; } static inline void generic_handle_irq_desc(unsigned int irq, struct irq_desc *desc) { desc->handle_irq(irq, desc); }
关于desc->handle_irq来历,在每个中断注册的时候,由gic_irq_domain_map根据hwirq号决定。
在gic_irq_domain_map的时候根据hw号决定handle,hw硬件中断号小于32指向handle_percpu_devid_irq,其他情况指向handle_fasteoi_irq。
void __irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained, const char *name) { ... desc->handle_irq = handle; desc->name = name; ... }
handle_percpu_devid_irq处理0~31的SGI/PPI类型中断,首先响应IAR,然后执行handler,最后发送EOI。
void handle_percpu_devid_irq(unsigned int irq, struct irq_desc *desc) { struct irq_chip *chip = irq_desc_get_chip(desc); struct irqaction *action = desc->action; void *dev_id = raw_cpu_ptr(action->percpu_dev_id); irqreturn_t res; kstat_incr_irqs_this_cpu(irq, desc); if (chip->irq_ack) chip->irq_ack(&desc->irq_data); trace_irq_handler_entry(irq, action); res = action->handler(irq, dev_id); trace_irq_handler_exit(irq, action, res); if (chip->irq_eoi) chip->irq_eoi(&desc->irq_data);-------------------调用gic_eoi_irq()函数 }
irq_enter和irq_exit显式地处理hardirq域计数,两者之间的部分属于中断上下文。
/* * Enter an interrupt context. */ void irq_enter(void) { rcu_irq_enter(); if (is_idle_task(current) && !in_interrupt()) { /* * Prevent raise_softirq from needlessly waking up ksoftirqd * here, as softirq will be serviced on return from interrupt. */ local_bh_disable(); tick_irq_enter(); _local_bh_enable(); } __irq_enter();---------------------------------------------显式增加hardirq域计数 } #define __irq_enter() \ do { \ account_irq_enter_time(current); \ preempt_count_add(HARDIRQ_OFFSET); \----------------显式增加hardirq域计数 trace_hardirq_enter(); \ } while (0) void irq_exit(void) { #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED local_irq_disable(); #else WARN_ON_ONCE(!irqs_disabled()); #endif account_irq_exit_time(current); preempt_count_sub(HARDIRQ_OFFSET);---------------------------显式减少hardirq域计数 if (!in_interrupt() && local_softirq_pending())--------------当前不处于中断上下文,且有pending的softirq,进行softirq处理。 invoke_softirq(); tick_irq_exit(); rcu_irq_exit(); trace_hardirq_exit(); /* must be last! */ }
4.2.1 中断上下文
判断当前进程是处于中断上下文,还是进程上下文依赖于preempt_count,这个变量在struct thread_info中。
preempt_count计数共32bit,从低到高依次是:
#define PREEMPT_BITS 8 #define SOFTIRQ_BITS 8 #define HARDIRQ_BITS 4 #define NMI_BITS 1
#define hardirq_count() (preempt_count() & HARDIRQ_MASK)-----------------硬件中断计数 #define softirq_count() (preempt_count() & SOFTIRQ_MASK)-----------------软中断计数 #define irq_count() (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \----包括NMI、硬中断、软中断三者计数 | NMI_MASK)) /* * Are we doing bottom half or hardware interrupt processing? * * in_irq() - We're in (hard) IRQ context * in_softirq() - We have BH disabled, or are processing softirqs * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled * in_serving_softirq() - We're in softirq context * in_nmi() - We're in NMI context * in_task() - We're in task context * * Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really * should not be used in new code. */ #define in_irq() (hardirq_count())----------------------------判断是否正在硬件中断上下文 #define in_softirq() (softirq_count())------------------------判断是否正在处理软中断或者禁止BH。 #define in_interrupt() (irq_count())--------------------------判断是否处于NMI、硬中断、软中断三者之一或者兼有上下文 #define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)---判断是否处于软中断上下文。 #define in_nmi() (preempt_count() & NMI_MASK)-----------------判断是否处于NMI上下文 #define in_task() (!(preempt_count() & \ (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))------判断是否处于进程上下文
思考:in_softirq()和in_serving_softirq()区别?in_interrupt()和in_task()中关于SOFTIRQ_MASK和SOFTIRQ_OFFSET区别?
4.3 handle_fasteoi_irq
handle_fsteoi_irq处理SPI类型的中断,将主要工作交给handle_irq_event()。
handle_irq_event_percpu()首先处理action->handler,有需要则唤醒中断内核线程,执行action->thread_fn。
void handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc) { struct irq_chip *chip = desc->irq_data.chip; raw_spin_lock(&desc->lock); if (!irq_may_run(desc)) goto out; desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING); kstat_incr_irqs_this_cpu(irq, desc); /* * If its disabled or no action available * then mask it and get out of here: */ if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {---如果该中断没有指定action描述符或该中断被关闭了IRQD_IRQ_DISABLED,设置该中断状态为IRQS_PENDING,且mask_irq()屏蔽该中断。 desc->istate |= IRQS_PENDING; mask_irq(desc); goto out; } if (desc->istate & IRQS_ONESHOT)----------------------------------------如果中断是IRQS_ONESHOT,不支持中断嵌套,那么应该调用mask_irq()来屏蔽该中断源。 mask_irq(desc); preflow_handler(desc);--------------------------------------------------取决于是否定义了freflow_handler() handle_irq_event(desc); cond_unmask_eoi_irq(desc, chip);----------------------------------------根据不同条件执行unmask_irq()解除中断屏蔽,或者执行irq_chip->irq_eoi发送EOI信号,通知GIC中断处理完毕。 raw_spin_unlock(&desc->lock); return; out: if (!(chip->flags & IRQCHIP_EOI_IF_HANDLED)) chip->irq_eoi(&desc->irq_data); raw_spin_unlock(&desc->lock); }
handle_irq_event调用handle_irq_event_percpu,执行action->handler(),如有需要唤醒内核中断线程执行action->thread_fn。
irqreturn_t handle_irq_event(struct irq_desc *desc) { struct irqaction *action = desc->action; irqreturn_t ret; desc->istate &= ~IRQS_PENDING;--------------------------清除IRQS_PENDING标志位 irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);---------设置IRQD_IRQ_INPROGRESS标志位,表示正在处理硬件中断。 raw_spin_unlock(&desc->lock); ret = handle_irq_event_percpu(desc, action); raw_spin_lock(&desc->lock); irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);-------清除IRQD_IRQ_INPROGRESS标志位,表示中断处理结束。 return ret; } irqreturn_t handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) { irqreturn_t retval = IRQ_NONE; unsigned int flags = 0, irq = desc->irq_data.irq; do {----------------------------------------------------遍历中断描述符中的action链表,依次执行每个action元素中的primary handler回调函数action->handler。 irqreturn_t res; trace_irq_handler_entry(irq, action); res = action->handler(irq, action->dev_id);---------执行struct irqaction的handler函数。 trace_irq_handler_exit(irq, action, res); if (WARN_ONCE(!irqs_disabled(),"irq %u handler %pF enabled interrupts\n", irq, action->handler)) local_irq_disable();--------------------------- switch (res) { case IRQ_WAKE_THREAD:-------------------------------去唤醒内核中断线程 /* * Catch drivers which return WAKE_THREAD but * did not set up a thread function */ if (unlikely(!action->thread_fn)) { warn_no_thread(irq, action);----------------输出一个打印表示没有中断处理函数 break; } __irq_wake_thread(desc, action);----------------唤醒此中断对应的内核线程 /* Fall through to add to randomness */ case IRQ_HANDLED:-----------------------------------已经处理完毕,可以结束。 flags |= action->flags; break; default: break; } retval |= res; action = action->next; } while (action); add_interrupt_randomness(irq, flags); if (!noirqdebug) note_interrupt(irq, desc, retval); return retval; }
4.3.1 唤醒中断内核线程
__irq_wake_thread唤醒对应中断的内核线程。
void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action) { /* * In case the thread crashed and was killed we just pretend that * we handled the interrupt. The hardirq handler has disabled the * device interrupt, so no irq storm is lurking. */ if (action->thread->flags & PF_EXITING) return; /* * Wake up the handler thread for this action. If the * RUNTHREAD bit is already set, nothing to do. */ if (test_and_set_bit(IRQTF_RUNTHREAD, &action->thread_flags))--------------若已经对IRQF_RUNTHREAD置位,表示已经处于唤醒中,该函数直接返回。 return; desc->threads_oneshot |= action->thread_mask;--------------------thread_mask在共享中断中,每一个action有一个比特位来表示。thread_oneshot每个比特位表示正在处理的共享oneshot类型中断的中断线程。 atomic_inc(&desc->threads_active);-------------------------------活跃中断线程计数 wake_up_process(action->thread);---------------------------------唤醒action的thread内核线程 }
4.3.2 创建内核中断线程
irq_thread在中断注册的时候,如果条件满足同时创建rq/xx-xx内核中断线程,线程优先级是49(99-50),调度策略是SCHED_FIFO。
static int __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new) { ... /* * Create a handler thread when a thread function is supplied * and the interrupt does not nest into another interrupt * thread. */ if (new->thread_fn && !nested) { struct task_struct *t; static const struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2,-------------------------------设置irq内核线程的优先级,在/proc/xxx/sched中看到的prio为MAX_RT_PRIO-1-sched_priority。 }; t = kthread_create(irq_thread, new, "irq/%d-%s", irq, new->name);--------------------------------------------------创建线程名为irq/xxx-xxx的内核线程,线程执行函数是irq_thread。 ... sched_setscheduler_nocheck(t, SCHED_FIFO, ¶m);----------------------设置进程调度策略为SCHED_FIFO。 /* * We keep the reference to the task struct even if * the thread dies to avoid that the interrupt code * references an already freed task_struct. */ get_task_struct(t); new->thread = t;-------------------------------------------------------将当前线程和irq_action关联起来 set_bit(IRQTF_AFFINITY, &new->thread_flags);--------------------------对中断线程设置CPU亲和性 } ... }
4.3.3 内核中断线程执行
irq_thread是中断线程的执行函数,在irq_wait_for_interrupt()中等待。
irq_wait_for_interrupt()中判断IRQTF_RUNTHREAD标志位,没有置位则schedule()换出CPU,进行睡眠。
直到__irq_wake_thread()置位了IRQTF_RUNTHREAD,并且wake_up_process()后,irq_wait_for_interrupt()返回0。
static int irq_thread(void *data) { struct callback_head on_exit_work; struct irqaction *action = data; struct irq_desc *desc = irq_to_desc(action->irq); irqreturn_t (*handler_fn)(struct irq_desc *desc, struct irqaction *action); if (force_irqthreads && test_bit(IRQTF_FORCED_THREAD, &action->thread_flags)) handler_fn = irq_forced_thread_fn; else handler_fn = irq_thread_fn; init_task_work(&on_exit_work, irq_thread_dtor); task_work_add(current, &on_exit_work, false); irq_thread_check_affinity(desc, action); while (!irq_wait_for_interrupt(action)) { irqreturn_t action_ret; irq_thread_check_affinity(desc, action); action_ret = handler_fn(desc, action);-----------执行中断内核线程函数 if (action_ret == IRQ_HANDLED) atomic_inc(&desc->threads_handled);----------增加threads_handled计数 wake_threads_waitq(desc);------------------------唤醒wait_for_threads等待队列 } /* * This is the regular exit path. __free_irq() is stopping the * thread via kthread_stop() after calling * synchronize_irq(). So neither IRQTF_RUNTHREAD nor the * oneshot mask bit can be set. We cannot verify that as we * cannot touch the oneshot mask at this point anymore as * __setup_irq() might have given out currents thread_mask * again. */ task_work_cancel(current, irq_thread_dtor); return 0; } static int irq_wait_for_interrupt(struct irqaction *action) { set_current_state(TASK_INTERRUPTIBLE); while (!kthread_should_stop()) { if (test_and_clear_bit(IRQTF_RUNTHREAD, &action->thread_flags)) {------------判断thread_flags是否设置IRQTF_RUNTHREAD标志位,如果设置则设置当前状态TASK_RUNNING并返回0。此处和__irq_wake_thread中设置IRQTF_RUNTHREAD对应。 __set_current_state(TASK_RUNNING); return 0; } schedule();-----------------------------------------换出CPU,在此等待睡眠 set_current_state(TASK_INTERRUPTIBLE); } __set_current_state(TASK_RUNNING); return -1; } static irqreturn_t irq_thread_fn(struct irq_desc *desc, struct irqaction *action) { irqreturn_t ret; ret = action->thread_fn(action->irq, action->dev_id);---执行中断内核线程函数,为request_threaded_irq注册中断参数thread_fn。 irq_finalize_oneshot(desc, action);---------------------针对oneshot类型中断收尾处理,主要是去屏蔽中断。 return ret; }
irq_finalize_oneshot()对ontshot类型的中断进行收尾操作。
static void irq_finalize_oneshot(struct irq_desc *desc, struct irqaction *action) { if (!(desc->istate & IRQS_ONESHOT) || action->handler == irq_forced_secondary_handler) return; again: chip_bus_lock(desc); raw_spin_lock_irq(&desc->lock); /* * Implausible though it may be we need to protect us against * the following scenario: * * The thread is faster done than the hard interrupt handler * on the other CPU. If we unmask the irq line then the * interrupt can come in again and masks the line, leaves due * to IRQS_INPROGRESS and the irq line is masked forever. * * This also serializes the state of shared oneshot handlers * versus "desc->threads_onehsot |= action->thread_mask;" in * irq_wake_thread(). See the comment there which explains the * serialization. */ if (unlikely(irqd_irq_inprogress(&desc->irq_data))) {-----------必须等待硬件中断处理程序清除IRQD_IRQ_INPROGRESS标志位,见handle_irq_event()。因为该标志位表示硬件中断处理程序正在处理硬件中断,直到硬件中断处理完毕才会清除该标志。 raw_spin_unlock_irq(&desc->lock); chip_bus_sync_unlock(desc); cpu_relax(); goto again; } /* * Now check again, whether the thread should run. Otherwise * we would clear the threads_oneshot bit of this thread which * was just set. */ if (test_bit(IRQTF_RUNTHREAD, &action->thread_flags)) goto out_unlock; desc->threads_oneshot &= ~action->thread_mask; if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data) && irqd_irq_masked(&desc->irq_data)) unmask_threaded_irq(desc);----------------------------------执行EOI或者去中断屏蔽。 out_unlock: raw_spin_unlock_irq(&desc->lock); chip_bus_sync_unlock(desc); }
至此一个中断的执行完毕。
4.4 如何保证IRQS_ONESHOT不嵌套?
5. 注册中断
5.1 中断、线程、中断线程化
中断处理程序包括上半部硬件中断处理程序,下半部处理机制,包括软中断、tasklet、workqueue、中断线程化。
当一个外设中断发生后,内核会执行一个函数来响应该中断,这个函数通常被称为中断处理程序或中断服务例程。
上半部硬件中断处理运行在中断上下文中,要求快速完成并且退出中断。
中断线程化是实时Linux项目开发的一个新特性,目的是降低中断处理对系统实时延迟的影响。
在LInux内核里,中断具有最高优先级,只要有中断发生,内核会暂停手头的工作转向中断处理,等到所有挂起等待的中断和软终端处理完毕后才会执行进程调度,因此这个过程会造成实时任务得不到及时处理。
中断上下文总是抢占进程上下文,中断上下文不仅是中断处理程序,还包括softirq、tasklet等,中断上下文成了优化Linux实时性的最大挑战之一。
5.2 中断注册接口
IRQF_*描述的中断标志位用于request_threaded_irq()申请中断时描述该中断的特性。
IRQS_*的中断标志位是位于struct irq_desc数据结构的istate成员,也即core_internal_state__do_not_mess_with_it。
IRQD_*是struct irq_data数据结构中的state_use_accessors成员一组中断标志位,通常用于描述底层中断状态。
关于IRQF_ONESHOT特别解释:必须在硬件中断处理结束之后才能重新使能中断;线程化中断处理过程中保持中断线处于关闭状态,直到该中断线上所有thread_fn执行完毕。
#define IRQF_TRIGGER_NONE 0x00000000 #define IRQF_TRIGGER_RISING 0x00000001---------------------------上升沿触发 #define IRQF_TRIGGER_FALLING 0x00000002--------------------------下降沿触发 #define IRQF_TRIGGER_HIGH 0x00000004-----------------------------高电平触发 #define IRQF_TRIGGER_LOW 0x00000008------------------------------地电平触发 #define IRQF_TRIGGER_MASK (IRQF_TRIGGER_HIGH | IRQF_TRIGGER_LOW | \ IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING)--------四种触发类型 #define IRQF_TRIGGER_PROBE 0x00000010 #define IRQF_SHARED 0x00000080-------------------------------多个设备共享一个中断号 #define IRQF_PROBE_SHARED 0x00000100-----------------------------中断处理程序允许sharing mismatch发生 #define __IRQF_TIMER 0x00000200------------------------------标记一个时钟中断 #define IRQF_PERCPU 0x00000400-------------------------------属于某个特定CPU的中断 #define IRQF_NOBALANCING 0x00000800------------------------------禁止在多CPU之间做中断均衡 #define IRQF_IRQPOLL 0x00001000------------------------------中断被用作轮询 #define IRQF_ONESHOT 0x00002000------------------------------一次性触发中断,不允许嵌套。 #define IRQF_NO_SUSPEND 0x00004000---------------------------在系统睡眠过程中不要关闭该中断 #define IRQF_FORCE_RESUME 0x00008000-----------------------------在系统唤醒过程中必须抢孩子打开该中断 #define IRQF_NO_THREAD 0x00010000----------------------------表示该中断不会给线程化 #define IRQF_EARLY_RESUME 0x00020000 #define IRQF_COND_SUSPEND 0x00040000 #define IRQF_TIMER (__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD) enum { IRQS_AUTODETECT = 0x00000001,-------------------处于自动侦测状态 IRQS_SPURIOUS_DISABLED = 0x00000002,----------------被视为“伪中断”并被禁用 IRQS_POLL_INPROGRESS = 0x00000008,------------------正处于轮询调用action IRQS_ONESHOT = 0x00000020,----------------------表示只执行一次,由IRQF_ONESHOT转换而来,在中断线程化执行完成后需要小心对待,见irq_finalize_oneshot()。 IRQS_REPLAY = 0x00000040,-----------------------重新发送一次中断 IRQS_WAITING = 0x00000080,----------------------处于等待状态 IRQS_PENDING = 0x00000200,----------------------该中断被挂起 IRQS_SUSPENDED = 0x00000800,--------------------该中断被暂停 }; enum { IRQD_TRIGGER_MASK = 0xf,-------------------------该中断触发类型 IRQD_SETAFFINITY_PENDING = (1 << 8), IRQD_NO_BALANCING = (1 << 10), IRQD_PER_CPU = (1 << 11), IRQD_AFFINITY_SET = (1 << 12), IRQD_LEVEL = (1 << 13), IRQD_WAKEUP_STATE = (1 << 14), IRQD_MOVE_PCNTXT = (1 << 15), IRQD_IRQ_DISABLED = (1 << 16),--------------------该中断处于关闭状态 IRQD_IRQ_MASKED = (1 << 17),------------------该中断被屏蔽中 IRQD_IRQ_INPROGRESS = (1 << 18),------------------该中断正在被处理中 IRQD_WAKEUP_ARMED = (1 << 19), IRQD_FORWARDED_TO_VCPU = (1 << 20), };
struct irqaction是每个中断的irqaction描述符。
struct irqaction { irq_handler_t handler;-----------primary handler函数指针 void *dev_id;----------------传递给中断处理程序的参数 void __percpu *percpu_dev_id; struct irqaction *next; irq_handler_t thread_fn;---------中断线程处理程序的函数指针 struct task_struct *thread;----------中断线程的task_struct数据结构 unsigned int irq;----------------Linux软件中断号 unsigned int flags;--------------注册中断时用的中断标志位,IRQF_*。 unsigned long thread_flags;------中断线程相关标志位 unsigned long thread_mask;-------在共享中断中,每一个action有一个比特位来表示。 const char *name;----------------中断线程名称 struct proc_dir_entry *dir; } ____cacheline_internodealigned_in_smp;
request_irq调用request_threaded_irq进行中断注册,只是少了一个thread_fn参数。这也是两则的区别所在,request_irq不能注册线程化中断。
irq:Linux软件中断号,不是硬件中断号。
handler:指primary handler,也即request_irq的中断处理函数handler。
thread_fn:中断线程化的处理函数。
irqflags:中断标志位,见IRQF_*解释。
devname:中断名称。
dev_id:传递给中断处理程序的参数。
handler和thread_fn分别被赋给action->handler和action->thread_fn,组合如下:
handler | thread_fn | ||
1 | √ | √ | 先执行handler,然后条件执行thread_fn。 |
2 | √ | × | 等同于request_irq() |
3 | × | √ | handler=irq_default_primary_handler |
4 | × | × | 返回-EINVAL |
很多request_threaded_irq()使用第3种组合,irq_default_primary_handler()返回IRQ_WAKE_THREAD,将工作交给thread_fn进行处理。
第2种组合相当于request_irq()。
第4种组合不被允许,因为中断得不到任何处理。
第1种组合较复杂,在handler根据实际情况返回IRQ_WAKE_THREAD(唤醒内核中断线程)或者IRQ_HANDLED(中断已经处理完毕,不需要唤醒中断内核线程)。
request_threaded_irq()对参数进行检查之后,分配struct irqaction并填充,然后将注册工作交给__setup_irq()。
static inline int __must_check request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags, const char *name, void *dev) { return request_threaded_irq(irq, handler, NULL, flags, name, dev); } int request_threaded_irq(unsigned int irq, irq_handler_t handler, irq_handler_t thread_fn, unsigned long irqflags, const char *devname, void *dev_id) { ... if (((irqflags & IRQF_SHARED) && !dev_id) ||-----------------------------共享中断设备必须传递啊dev_id参数来区分是哪个共享外设的中断 (!(irqflags & IRQF_SHARED) && (irqflags & IRQF_COND_SUSPEND)) || ((irqflags & IRQF_NO_SUSPEND) && (irqflags & IRQF_COND_SUSPEND))) return -EINVAL; desc = irq_to_desc(irq);--------------------------------------------------通过Linux中断号找到对应中断描述符struct irq_desc。 if (!desc) return -EINVAL; ... if (!handler) { if (!thread_fn) return -EINVAL;---------------------------------------------------handler和thread_fn不能同时为NULL handler = irq_default_primary_handler;--------------------------------没有设置handler,irq_default_primary_handler()默认返回IRQ_WAKE_THREAD。 } action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);-------------------分配struct irqaction,并填充相应成员 if (!action) return -ENOMEM; action->handler = handler; action->thread_fn = thread_fn; action->flags = irqflags; action->name = devname; action->dev_id = dev_id; chip_bus_lock(desc);-------------------------------------------------------调用desc->irq_data.chip->irq_bus_lock()进行加锁保护 retval = __setup_irq(irq, desc, action); chip_bus_sync_unlock(desc); if (retval) kfree(action); ... return retval; }
5.3 __setup_irq
一张图
__setup_irq()首先做参数检查,然后根据需要创建中断内核线程,这期间处理中断嵌套、oneshot、中断共享等问题。
还设置了中断触发类型设置,中断使能等工作。最后根据需要唤醒中断内核线程,并创建此中断相关sysfs节点。
/* * Internal function to register an irqaction - typically used to * allocate special interrupts that are part of the architecture. */ static int __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new) { struct irqaction *old, **old_ptr; unsigned long flags, thread_mask = 0; int ret, nested, shared = 0; cpumask_var_t mask; if (!desc) return -EINVAL; if (desc->irq_data.chip == &no_irq_chip)----------------------表示没有正确初始化中断控制器,对于GICv2在gic_irq_domain_alloc()中指定chip为gic_chip。 return -ENOSYS; if (!try_module_get(desc->owner)) return -ENODEV; /* * Check whether the interrupt nests into another interrupt * thread. */ nested = irq_settings_is_nested_thread(desc);-----------------对于设置了_IRQ_NESTED_THREAD嵌套类型的中断描述符,必须指定thread_fn。 if (nested) { if (!new->thread_fn) { ret = -EINVAL; goto out_mput; } /* * Replace the primary handler which was provided from * the driver for non nested interrupt handling by the * dummy function which warns when called. */ new->handler = irq_nested_primary_handler; } else { if (irq_settings_can_thread(desc))-----------------------判断该中断是否可以被线程化,如果没有设置_IRQ_NOTHREAD表示可以被强制线程化。 irq_setup_forced_threading(new); } /* * Create a handler thread when a thread function is supplied * and the interrupt does not nest into another interrupt * thread. */ if (new->thread_fn && !nested) {-----------------------------对不支持嵌套的线程化中断创建一个内核线程,实时SCHED_FIFO,优先级为50的实时线程。 struct task_struct *t; static const struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2, }; t = kthread_create(irq_thread, new, "irq/%d-%s", irq, new->name);-----------------------------------由irq、中断号、中断名组成的中断线程名,处理函数是irq_thread()。 if (IS_ERR(t)) { ret = PTR_ERR(t); goto out_mput; } sched_setscheduler_nocheck(t, SCHED_FIFO, ¶m); get_task_struct(t); new->thread = t; set_bit(IRQTF_AFFINITY, &new->thread_flags); } if (!alloc_cpumask_var(&mask, GFP_KERNEL)) { ret = -ENOMEM; goto out_thread; } /* * Drivers are often written to work w/o knowledge about the * underlying irq chip implementation, so a request for a * threaded irq without a primary hard irq context handler * requires the ONESHOT flag to be set. Some irq chips like * MSI based interrupts are per se one shot safe. Check the * chip flags, so we can avoid the unmask dance at the end of * the threaded handler for those. */ if (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)----------表示该中断控制器不支持中断嵌套,所以flags去掉IRQF_ONESHOT。 new->flags &= ~IRQF_ONESHOT; raw_spin_lock_irqsave(&desc->lock, flags); old_ptr = &desc->action; old = *old_ptr; if (old) {-----------------------------------------------------old指向desc->action指向的链表,old不为空说明已经有中断添加到中断描述符irq_desc中,说明这是一个共享中断。shared=1。 ... /* add new interrupt at end of irq queue */ do { /* * Or all existing action->thread_mask bits, * so we can find the next zero bit for this * new action. */ thread_mask |= old->thread_mask; old_ptr = &old->next; old = *old_ptr; } while (old); shared = 1; } /* * Setup the thread mask for this irqaction for ONESHOT. For * !ONESHOT irqs the thread mask is 0 so we can avoid a * conditional in irq_wake_thread(). */ if (new->flags & IRQF_ONESHOT) { /* * Unlikely to have 32 resp 64 irqs sharing one line, * but who knows. */ if (thread_mask == ~0UL) { ret = -EBUSY; goto out_mask; } new->thread_mask = 1 << ffz(thread_mask); } else if (new->handler == irq_default_primary_handler &&---------非IRQF_ONESHOT类型中断,且handler使用默认irq_default_primary_handler(),如果中断触发类型是LEVEL,如果中断出发后不清中断容易引发中断风暴。提醒驱动开发者,没有primary handler且中断控制器不支持硬件oneshot,必须显式指定IRQF_ONESHOT表示位。 !(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) { pr_err("Threaded irq requested with handler=NULL and !ONESHOT for irq %d\n", irq); ret = -EINVAL; goto out_mask; } if (!shared) {-------------------------------------------------非共享中断情况 ret = irq_request_resources(desc); if (ret) { pr_err("Failed to request resources for %s (irq %d) on irqchip %s\n", new->name, irq, desc->irq_data.chip->name); goto out_mask; } init_waitqueue_head(&desc->wait_for_threads); /* Setup the type (level, edge polarity) if configured: */ if (new->flags & IRQF_TRIGGER_MASK) { ret = __irq_set_trigger(desc, irq,-------------------调用gic_chip->irq_set_type设置中断触发类型。 new->flags & IRQF_TRIGGER_MASK); if (ret) goto out_mask; } desc->istate &= ~(IRQS_AUTODETECT | IRQS_SPURIOUS_DISABLED | \ IRQS_ONESHOT | IRQS_WAITING); irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);---------清IRQD_IRQ_INPROGRESS标志位 if (new->flags & IRQF_PERCPU) { irqd_set(&desc->irq_data, IRQD_PER_CPU); irq_settings_set_per_cpu(desc); } if (new->flags & IRQF_ONESHOT) desc->istate |= IRQS_ONESHOT; if (irq_settings_can_autoenable(desc)) irq_startup(desc, true); else /* Undo nested disables: */ desc->depth = 1; /* Exclude IRQ from balancing if requested */ if (new->flags & IRQF_NOBALANCING) { irq_settings_set_no_balancing(desc); irqd_set(&desc->irq_data, IRQD_NO_BALANCING); } /* Set default affinity mask once everything is setup */ setup_affinity(irq, desc, mask); } else if (new->flags & IRQF_TRIGGER_MASK) { .. } new->irq = irq; *old_ptr = new; irq_pm_install_action(desc, new); /* Reset broken irq detection when installing new handler */ desc->irq_count = 0; desc->irqs_unhandled = 0; /* * Check whether we disabled the irq via the spurious handler * before. Reenable it and give it another chance. */ if (shared && (desc->istate & IRQS_SPURIOUS_DISABLED)) { desc->istate &= ~IRQS_SPURIOUS_DISABLED; __enable_irq(desc, irq); } raw_spin_unlock_irqrestore(&desc->lock, flags); /* * Strictly no need to wake it up, but hung_task complains * when no hard interrupt wakes the thread up. */ if (new->thread) wake_up_process(new->thread);------------------------------如果该中断被线程化,那么就唤醒该内核线程。这里每个中断对应一个线程。 register_irq_proc(irq, desc);----------------------------------创建/proc/irq/xxx/目录及其节点。 new->dir = NULL; register_handler_proc(irq, new);-------------------------------以action->name创建目录 free_cpumask_var(mask); return 0; ... }
irq_setup_forced_threading()判断是否强制当前中断线程化,然后对thread_flags置位IRQTF_FORCED_THREAD表示此中断被强制线程化。
将原来的primary handler弄到中断线程中去执行,原来的primary handler换成irq_default_primary_handler。
并设置secondary的primary handler指向irq_forced_secondary_handler(),原来的thread_fn移到secondary的中线程中执行。
static int irq_setup_forced_threading(struct irqaction *new) { if (!force_irqthreads)---------------------------------------------如果内核启动参数包含threadirqs,则支持强制线程化。或者CONFIG_PREEMPT_RT_BASE实时补丁打开,这里也强制线程化。 return 0; if (new->flags & (IRQF_NO_THREAD | IRQF_PERCPU | IRQF_ONESHOT))----和线程化矛盾的标志位。 return 0; new->flags |= IRQF_ONESHOT;----------------------------------------强制线程化的中断都置位IRQF_ONESHOT。 if (new->handler != irq_default_primary_handler && new->thread_fn) { /* Allocate the secondary action */ new->secondary = kzalloc(sizeof(struct irqaction), GFP_KERNEL); if (!new->secondary) return -ENOMEM; new->secondary->handler = irq_forced_secondary_handler; new->secondary->thread_fn = new->thread_fn; new->secondary->dev_id = new->dev_id; new->secondary->irq = new->irq; new->secondary->name = new->name; } /* Deal with the primary handler */ set_bit(IRQTF_FORCED_THREAD, &new->thread_flags); new->thread_fn = new->handler; new->handler = irq_default_primary_handler; return 0; }
setup_irq()、request_threaded_irq()、request_irq()都是对__setup_irq()的包裹。
request_irq()调用request_threaded_irq(),只是少了thread_fn。
request_thraded_irq()和setup_irq()的区别在于,setup_irq()入参是struct irqaction ,而request_threaded_irq()在内部组装struct irqaction。
6. 一个中断的生命
经过上面的分析可以看出一个中断从产生、执行,到最终结束的流程。这里我们用树形代码路径来简要分析一下一个中断的生命周期。
vector_irq()->vector_irq()->__irq_svc()
->svc_entry()--------------------------------------------------------------------------保护中断现场
->irq_handler()->gic_handle_irq()------------------------------------------------具体到GIC中断控制器对应的就是gic_handle_irq(),此处从架构相关进入了GIC相关处理。
->GIC_CPU_INTACK--------------------------------------------------------------读取IAR寄存器,响应中断。
->handle_domain_irq()
->irq_enter()------------------------------------------------------------------------进入硬中断上下文
->generic_handle_irq()
->generic_handle_irq_desc()->handle_fasteoi_irq()--------------------根据中断号分辨不同类型的中断,对应不同处理函数,这里中断号取大于等于32。
->handle_irq_event()->handle_irq_event_percpu()
->action->handler()-----------------------------------------------------------对应到特定中断的处理函数,即上半部。
->__irq_wake_thread()-----------------------------------------------------如果中断函数处理返回IRQ_WAKE_THREAD,则唤醒中断线程进行处理,但不是立即执行中断线程。
->irq_exit()---------------------------------------------------------------------------退出硬中断上下文。视情况处理软中断。
->invoke_softirq()-----------------------------------------------------------------处理软中断,超出一定条件任务就会交给软中断线程处理。
->GIC_CPU_EOI--------------------------------------------------------------------写EOI寄存器,表示结束中断。至此GIC才会接收新的硬件中断,此前一直是屏蔽硬件中断的。
->svc_exit-------------------------------------------------------------------------------恢复中断现场
从上面的分析可以看出:
- 中断上半部的处理是关硬件中断的,这里的关硬件中断是GIC就不接收中断处理。直到写EOI之后,GIC仲裁单元才会重新选择中断进行处理。
- 软中断运行于软中断上下文中,但是仍然是关硬件中断的,这里需要特别注意,软中断需要快速处理并且不能睡眠。
- 不是所有软中断都运行于软中断上下文中,部分软中断任务可能会交给ksoftirqd线程处理。
- 包括IRQ_WAKE_THREAD、ksoftirqd、woker等唤醒线程的情况,都不会在中断上下文中进行处理。中断上下文中所做的处理只是唤醒,执行时机交给系统调度。
- 如果要提高Linux实时性,有两个要点:一是将上半部线程化;另一个是将软中断都交给ksoftirqd线程处理。
来源:https://www.cnblogs.com/arnoldlu/p/8659981.html