linux-kernel - Re: [PATCH] pinctrl: msm: Pass along set

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Message-ID: <20180710203805.GA14825@codeaurora.org>
Date:   Tue, 10 Jul 2018 14:38:05 -0600
From:   Lina Iyer <ilina@...eaurora.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, swboyd@...omium.org
Subject: Re: [PATCH] pinctrl: msm: Pass along set_wake failures

On Tue, Jul 10 2018 at 12:53 -0600, Evan Green wrote:
>On Mon, Jul 9, 2018 at 10:27 AM Bjorn Andersson
><bjorn.andersson@...aro.org> wrote:
>>
>> Sorry for not getting back to you in a timely manner Evan, I wanted to
>> read up more on the details of how this is supposed to work. I still
>> haven't done so, but here's my concern:
>>
>> When we power down the SoC we're no longer powering either the TLMM or
>> the GIC, so the MPM or PDC is used to waking the system on some set of
>> triggers. As such set_wake on an individual pin or irq should be routed
>> to the MPM/PDC driver, which (in the PDC case) is implemented using
>> hierarchical irq domains.
>>
>> As such I think that we shouldn't toggle the wake property of the
>> summary pin at all; i.e. the patch should remove that call rather than
>> propagating what I believe is a constant failure.
>>
>> Regards,
>> Bjorn
>
>Hi Bjorn,
>That's okay, I always feel bad pinging. Thanks for the thoughtful
>response. Stephen and I are starting to think about how wake
>interrupts should work with regard to the PDC, and we're at a place
>where we're a bit unsure of the path forward.
>
>Our understanding is the downstream kernel had an interrupt hierarchy
>of GIC > PDC > TLMM & everybody else. In the downstream world PDC
>acted transparently, forwarding most requests directly onto the GIC,
>but quietly handling wake interrupts as well. With the upstream PDC
>driver, the #interrupt-cells got changed to 2, and it seemed like
>folks didn't like the idea that PDC was acting transparently. Correct
>me if I'm wrong there. So now we're sort of unsure about how to wire
>in PDC. If we make everybody an interrupt child of PDC, then we lose
>the ability to specify the third GIC parameter, and we're stuck
>expressing interrupts with respect to PDC pins, which is an awkward
>mental translation.
Its an unfortunate side effect of the design. Drivers will have to
request the PDC pin for wakeup IRQs.

>In this world, does TLMM need to do direct-connect
>stuff to get wake-able GPIO interrupts working? It would kind of have
>a foot in both worlds, with its summary interrupt as a GIC interrupt
>but the wakeable ones as parented by PDC?
>
With GPIOs, I am trying to hack the TLMM driver to request a PDC pin,
when the IRQ associated with the GPIO is requested as a wakeup
interrupt. In that case, the TLMM driver would do the GPIO->PDC pin
translation and request it. There is no hierarchy between TLMM and PDC.

Will try a RFC patch in a week or two.

-- Lina

>So anyway, with regard to this patch, I'm happy to create a second
>spin that simply removes this function, but for me at least it brought
>up some larger questions we've been wrestling with.
>-Evan
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