移植Linux-5.4+内核到4412开发板

前言
ITOP-4412开发板被Linux官方支持，所以我们在4412上学习新的内核是非常方便的，本文作者是4412精英群8群一位技术高手，接下来，我们一起来欣赏下他的表演。
环境说明
OS版本
Ubuntu 20 LTS

交叉编译环境配置
~$ sudo apt install gcc-arm-linux-gnueabihf
~$ sudo apt install flex
~$ sudo apt install bison
~$ sudo apt install u-boot-tools
目标开发板
CPU (Exynos4412，四核Cortex-A9，主频为1.4GHz-1.6GHz)
RAM (1GB 双通道 DDR3)
ROM (8GB EMMC)
其他请见官网链接
1. 下载源码
~$ git clone https://github.com/jason416/linux.gi
Note:移植好的源码见博主github仓库的iTop4412分支。
2. 配置内核
2.1 进入内核源码目录
~/linux-5.4$ ls
arch COPYING  Documentation  include  Kbuild lib       Makefile  README security  usr
block  CREDITS  drivers       init    Kconfig  LICENSES    mm       samples  sound    virt
certs  crypto fs          ipc    kernel MAINTAINERS  net    scripts  tools
jason@jason-vm2:~/arm-develop/linux$
2.2 修改内核配置
说明：
Note: 官方提供了所有三星系列的默认配置，需要先生成一个exynos的配置为基础，再上面再修改成跟板子一致的配置选项即可。
为了避免每次都需要指定ARCH和CROSS_COMPILE变量，可以直接在顶层Makefile直接指定好，如下所示：

选择系统类型
System Type --->

Samsung EXYNOS  --->
      --- Samsung EXYNOS
      [] SAMSUNG EXYNOS3
SAMSUNG EXYNOS4
      [] SAMSUNG EXYNOS5
         *** EXYNOS SoCs ***
      -*- SAMSUNG EXYNOS4210
SAMSUNG EXYNOS4412

配置调试串口 - 设置为UART2
Kernel hacking --->
Kernel low-level debugging functions (read help!)
      Kernel low-level debugging port (Use Samsung S3C UART 2 for low-level debug)  --->
开启串口调试驱动
Device Drivers  --->
   Character devices  --->
      Serial drivers  --->
      <*> Samsung SoC serial support
Samsung SoC serial debug
Support for console on Samsung SoC serial port
开启DM96XX网卡驱动
Device Drivers --->
Network device support  --->
      <*> USB Network Adapters  --->
      <*>    Davicom DM96xx based USB 10/100 ethernet devices
设置内核压缩模式为LZMA(非必须，可减小文件大小)
General setup  --->
   ()  Build ID Salt
      Kernel compression mode (LZMA)  --->
编译内核
~/linux-5.4$ make uImage LOADADDR=0x40008000 -j$(nproc)
...
  OBJCOPY arch/arm/boot/zImage
  Kernel: arch/arm/boot/zImage is ready
  UIMAGE  arch/arm/boot/uImage
Image Name: Linux-5.4.47
Created:    Sun Jun 21 22:41:40 2020
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 5337464 Bytes = 5212.37 KiB = 5.09 MiB
Load Address: 40008000
Entry Point:  40008000
  Kernel: arch/arm/boot/uImage is ready
   这里需要指定LOADADDR变量，才能生成正确的uImage文件。因为在uboot启动内核时，会先解析uImage中的前64B头信息，定义如下：

3. 修改设备树（以适配开发板）
3.1 说明
在前面的步骤完成后，已经能够编译出可以运行的内核了，但是最后还需要根据板子的差异性，对设备树文件进行调整，以适配目标板。
3.2 修改
屏蔽掉firmware节点(安全相关，不启用，也不知道怎么用…)
修改bus_dmc 节点devfreq-events为devfreq-event
修改regulators 节点参数(参考原理图中的参数)
修改如下：
--- a/arch/arm/boot/dts/exynos4412-itop-scp-core.dtsi
+++ b/arch/arm/boot/dts/exynos4412-itop-scp-core.dtsi
@@ -23,10 +23,12 @@
   reg = <0x40000000 0x40000000>;
};
+#if 0
firmware@203f000 {
   compatible = "samsung,secure-firmware";
   reg = <0x0203F000 0x1000>;
};
+#endif
fixed-rate-clocks {
   xxti {
@@ -70,7 +72,7 @@
};
&bus_dmc {
-  devfreq-events = <&ppmu_dmc0_3>, <&ppmu_dmc1_3>;
+  devfreq-event = <&ppmu_dmc0_3>, <&ppmu_dmc1_3>;
vdd-supply = <&buck1_reg>;
status = "okay";
};
@@ -167,8 +169,8 @@
   regulators {
   ldo1_reg: LDO1 {
      regulator-name = "VDD_ALIVE";
-       regulator-min-microvolt = <1100000>;
-       regulator-max-microvolt = <1100000>;
+       regulator-min-microvolt = <1000000>;
+       regulator-max-microvolt = <1000000>;
      regulator-always-on;
      regulator-boot-on;
      op_mode = <1>; /* Normal Mode */
@@ -230,8 +232,8 @@
   ldo9_reg: LDO9 {
      regulator-name = "VDD33_LCD";
-       regulator-min-microvolt = <3300000>;
-       regulator-max-microvolt = <3300000>;
+       regulator-min-microvolt = <3000000>;
+       regulator-max-microvolt = <3000000>;
      op_mode = <1>; /* Normal Mode */
   };
@@ -252,8 +254,8 @@
   ldo12_reg: LDO12 {
      regulator-name = "VDD33_UOTG";
-       regulator-min-microvolt = <3300000>;
-       regulator-max-microvolt = <3300000>;
+       regulator-min-microvolt = <3000000>;
+       regulator-max-microvolt = <3000000>;
      regulator-always-on;
      op_mode = <1>; /* Normal Mode */
   };
@@ -300,8 +302,8 @@
   /* Used by HSIC */
   ldo18_reg: LDO18 {
      regulator-name = "VDDIOPERI_28";
-       regulator-min-microvolt = <3300000>;
-       regulator-max-microvolt = <3300000>;
+       regulator-min-microvolt = <2800000>;
+       regulator-max-microvolt = <2800000>;
      regulator-always-on;
      op_mode = <1>; /* Normal Mode */
   };
@@ -313,15 +315,15 @@
   ldo20_reg: LDO20 {
      regulator-name = "VDD28_CAM";
-       regulator-min-microvolt = <1800000>;
-       regulator-max-microvolt = <2800000>;
+       regulator-min-microvolt = <3000000>;
+       regulator-max-microvolt = <3000000>;
      op_mode = <1>; /* Normal Mode */
   };
   ldo21_reg: LDO21 {
      regulator-name = "VDD28_AF";
-       regulator-min-microvolt = <1800000>;
-       regulator-max-microvolt = <2800000>;
+       regulator-min-microvolt = <3000000>;
+       regulator-max-microvolt = <3000000>;
      op_mode = <1>; /* Normal Mode */
   };
@@ -341,8 +343,8 @@
   ldo24_reg: LDO24 {
      regulator-name = "VDD33_A31";
-       regulator-min-microvolt = <3300000>;
-       regulator-max-microvolt = <3300000>;
+       regulator-min-microvolt = <3000000>;
+       regulator-max-microvolt = <3000000>;
      op_mode = <1>; /* Normal Mode */
   };
@@ -430,8 +432,8 @@
   buck7_reg: BUCK7 {
      regulator-name = "pvdd_buck7";
-       regulator-min-microvolt = <750000>;
-       regulator-max-microvolt = <2000000>;
+       regulator-min-microvolt = <2050000>;
+       regulator-max-microvolt = <2050000>;
      regulator-boot-on;
      regulator-always-on;
      op_mode = <1>; /* Normal Mode */
3.3 编译dts
~/linux-5.4$ make dtbs
4. 启动测试
根据另一个专题《Uboot-2017-11移植DM9621网卡专题》移植的支持网络功能的uboot，和移植的ubuntu-base-20.04-base-armhf文件系统（下篇文章更新移植方法），可以直接tftp测试内核，效果如下：

到这一步，移植工作就完成了，是不是觉得很容易呢~

更多内容关注公众号噢：

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来源：oschina

链接：https://my.oschina.net/u/3005926/blog/4321297

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