Inter processor Interrrupts in ARM cortex A9 ( How To write an handler for Software generated Interrupt ( ARM) in Linux? )

Question

I read that the Software generated interrupts in ARM are used as Inter-processor interrupts. I can also see that 5 of those interrupts are already in use. I also know that A

Answer 1

Does any one have an idea how to write a handler for SGI in Linux?

As you didn't give the Linux version, I will assume you work with the latest (or at least recent). The ARM GIC has device tree bindings. Typically, you need to specify the SGI interrupt number in a device tree node,

 ipc: ipc@address {
        compatible = "company,board-ipc"; /* Your driver */
        reg = 
;
        interrupts = <1 SGI 0x02>;  /* SGI is your CPU interrupt. */
        status = "enabled";
 };

The first number in the interrupt stanza denotes a PPI. The SGI will probably be between 0-15 as this is where the SGI interrupts are routed (at least on a Cortex-A5).

Then you can just use the platform_get_irq() in your driver to get the PPI (peripheral private interrupt). I guess that address is the shared memory (physical) where you wish to do the communications; maybe reg is not appropriate, but I think it will work. This area will be remapped by the Linux MMU and you can use it with,

res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
mem = devm_ioremap_resource(dev, res);

The address in the device tree above is a hex value of the physical address. The platform_get_irq() should return an irq number which you can use with the request_irq() family of functions. Just connect this to your routine.

Edit: Unfortunately, interrupts below 16 are forbidden by the Linux irq-gic.c. For example, gic_handle_irq(), limits handler to interrupts between 16 and 1020. If SMP is enabled, then handle_IPI() is called for the interrupts of interest. gic_raise_softirq() can be used to signal an interrupt. To handle the SGI with the current Linux, smp.c needs additional enum ipi_msg_type values and code to handle these in handle_IPI(). It looks like newer kernels (3.14+ perhaps?) may add a set_ipi_handler() to smp.c to make such a modification unneeded.