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

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Message-ID: <CAE=gft5+oOFv8y-XCtiQ8mc7gQ1FFSK0+bPk=mJu--ovLfDDJg@mail.gmail.com>
Date:   Tue, 10 Jul 2018 10:58:02 -0700
From:   Evan Green <evgreen@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     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,
        Lina Iyer <ilina@...eaurora.org>
Subject: Re: [PATCH] pinctrl: msm: Pass along set_wake failures

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. 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?

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