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From:   Pintu Kumar <pintu.ping@gmail.com>
Date:   Fri, 11 May 2018 17:07:37 +0530
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Subject: Re: Delivery Status Notification (Failure)
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        Russell King - ARM Linux <linux@armlinux.org.uk>,
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Hi,

I need one help.
I am using i.MX7 Sabre board with kernel version 4.1.15

Let's say I am interested in GPIO number: 21
I wanted to set CPU affinity for particular GPIO->IRQ number, so I
tried the below steps:
root@10:~# echo 21 > /sys/class/gpio/export
root@10:~# echo "rising" > /sys/class/gpio/gpio21/edge
root@10:~# cat /proc/interrupts | grep 21
  47: 0 0 gpio-mxc 21 Edge gpiolib
root@10:~# cat /sys/class/gpio/gpio21/direction
in
root@10:~# cat /proc/irq/47/smp_affinity
3
root@10:~# echo 2 > /proc/irq/47/smp_affinity
-bash: echo: write error: Input/output error

But I get input/output error.
When I debug further, found that irq_can_set_affinity is returning 0:
[    0.000000] genirq: irq_can_set_affinity (0): balance: 1,
irq_data.chip: a81b7e48, irq_set_affinity:   (null)
[    0.000000] write_irq_affinity: FAIL

I also tried first setting /proc/irq/default_smp_affinity to 2 (from 3).
This change is working, but the smp_affinity setting for the new IRQ
is not working.

When I try to set smp_affinity for mmc0, then it works.
# cat /proc/interrupts | grep mmc
295:         55          0     GPCV2  22 Edge      mmc0
296:          0          0     GPCV2  23 Edge      mmc1
297:         52          0     GPCV2  24 Edge      mmc2

root@10:~# echo 2 > /proc/irq/295/smp_affinity
root@10:~#


So, I wanted to know what are the conditions for which setting
smp_affinity for an IRQ will work ?

Is there any way by which I can set CPU affinity to a GPIO -> IRQ ?
Whether, irq_set_affinity_hint() will work in this case ?


Thanks,
Pintu