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From:   Pintu Kumar <pintu.ping@gmail.com>
Date:   Fri, 11 May 2018 20:07:33 +0530
Message-ID: <CAOuPNLgRHCasmsXTVwcy5ohq8TYjbr4MThxm4Q-HFWihJ7ARww@mail.gmail.com>
Subject: Re: Delivery Status Notification (Failure)
To:     Lucas Stach <l.stach@pengutronix.de>
Cc:     Russell King - ARM Linux <linux@armlinux.org.uk>,
        open list <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        kernelnewbies@kernelnewbies.org
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On Fri, May 11, 2018 at 6:34 PM, Lucas Stach <l.stach@pengutronix.de> wrote:
> Am Freitag, den 11.05.2018, 13:39 +0100 schrieb Russell King - ARM Linux:
>> On Fri, May 11, 2018 at 05:07:37PM +0530, Pintu Kumar wrote:
>> > 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 ?
>>
>> IRQ affinity is only supported where interrupts are _directly_ wired to
>> the GIC.  It's the GIC which does the interrupt steering to the CPU
>> cores.
>>
>> Interrupts on downstream interrupt controllers (such as GPCV2) have no
>> ability to be directed independently to other CPUs - the only possible
>> way to change the mapping is to move _all_ interrupts on that controller,
>> and any downstream chained interrupts at GIC level.
>>
>> Hence why Interrupt 295 has no irq_set_affinity function: there is no way
>> for the interrupt controller itself to change the affinity of the input
>> interrupt.
>
> The GPCv2 though is a secondary IRQ controller which has a 1:1 mapping
> of its input IRQs to the upstream GIC IRQ lines. Affinity can thus be
> handled by forwarding the request to the GIC by
> irq_chip_set_affinity_parent().
>
> As this is handled correctly in the upstream kernel since the first
> commit introducing support for the GPCv2, it seems the issue is only
> present in some downstream kernel.
>

OK. Thanks so much for your reply.

I saw some of the drivers using irq_set_affinity_hint() to force the
IRQ affinity to a particular CPU.
This is the sample:
{
cpumask_clear(mask);
cpumask_set_cpu(cpu, mask);
irq_set_affinity_hint(irq, mask);
}

Whether this logic will work for a particular GPIO pin ?


> Regards,
> Lucas