Linux/AM5726: Configuring interrupt priorities

Hi,

Linux kernel is not very flexible when it comes to IRQ prioritization & guaranteeing a certain scheduling delay (especially the non-RT linux kernels).

There is the possibility to use threads with different priorities within your system and call the ISR within these threads, as explained by Ron in this post:
  

From a hardware perspective ARM core provides some level of IRQ prioritization, see ARM TRM:
  

however you should also configure the IRQ_CROSSBAR to have the different gpio interrupts mapped to a correct interrupt lines of the ARM INTC. 

Best Regards,
Yordan

Hi David,

You can try with nice value to adjust threads/processes priorities.

If that doesn't help you can adjust GPIO priorities in A15 GIC registers.

linux-4.14.79/arch/arm/boot/dts/dra7.dtsi

linux-4.14.79/drivers/irqchip/irq-gic.c

linux-4.14.79/Documentation/devicetree/bindings/interrupt-controller/arm,gic.txt

linux-4.14.79/drivers/irqchip/irq-crossbar.c

linux-4.14.79/Documentation/devicetree/bindings/arm/omap/crossbar.txt

Regards,
Pavel

Hi Yordan,

Thank for the response. We are more concerned about the situation described below than interrupt-delays:

Gpio pin-A and gpio-pin-B, both using level interrupts, and pin-A having higher priority. We want make sure the ISR for pin-A will be called when both pin-A and pin-B are raised.

1. pin-A and pin-B are both low.
2. pin-B set to Hi, pin-B ISR is called.
3. pin-A set to Hi (while pin-B ISR is still being executed)
4. pin-B ISR (from step 2) completed
5. <pin-A and pin-B are still Hi>

In step 5 we want to be sure pin-A ISR is called instead of pin-B ISR

Hi Pavel, 

Thanks for the response.
Could you provide an example on which register I would need modify to make 1 GPIO have higher priority than another one. For example, if I wanted gpio5-7 to have higher priority than gpio7-3.

Thank you,
Regards,
David