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From:   Pintu Kumar <pintu.ping@gmail.com>
Date:   Mon, 14 May 2018 17:42:29 +0530
Message-ID: <CAOuPNLiFr3qbNVAwF4wj2aAG0UXRVsgRo-8JfaKFCsoL+Ggk9w@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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Hi,

Is there any work around possible to set IRQ affinity for some GPIO interrupt ?
How to avoid CPU0 to receive the current GPIO interrupt ?
How do we assign GPIO interrupts to any CPU other than CPU0 ?
Is it possible to isolate CPU0 for a sometime, from my GPIO driver so
that GPIO interrupt can be served by another CPU ?

Need your inputs to decide whether it is still possible to set
affinity for GPIO interrupt, or its impossible ?


Thanks,
Pintu


On Fri, May 11, 2018 at 8:07 PM, Pintu Kumar <pintu.ping@gmail.com> wrote:
> 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