linux-kernel - Re: [PATCH 4/7] dt-bindings: sdm845-pinctrl: add wakeup interrupt parent for GPIO

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Date:   Tue, 12 Feb 2019 09:05:31 -0700
From:   Lina Iyer <ilina@...eaurora.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Stephen Boyd <sboyd@...nel.org>, Evan Green <evgreen@...omium.org>,
        Marc Zyngier <marc.zyngier@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Raju P.L.S.S.S.N" <rplsssn@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 4/7] dt-bindings: sdm845-pinctrl: add wakeup interrupt
 parent for GPIO

On Wed, Jan 09 2019 at 12:37 -0700, Rob Herring wrote:
>On Wed, Jan 9, 2019 at 11:31 AM Lina Iyer <ilina@...eaurora.org> wrote:
>>
>> On Tue, Jan 08 2019 at 07:49 -0700, Rob Herring wrote:
>> >On Mon, Jan 7, 2019 at 12:51 PM Lina Iyer <ilina@...eaurora.org> wrote:
>> >>
>> >> On Fri, Dec 28 2018 at 17:07 -0700, Rob Herring wrote:
>> >> >On Wed, Dec 19, 2018 at 03:11:02PM -0700, Lina Iyer wrote:
>> >> >> SDM845 SoC has an always-on interrupt controller (PDC) with select GPIO
>> >> >> routed to the PDC as interrupts that can be used to wake the system up
>> >> >> from deep low power modes and suspend.
>> >> >>
>> >> >> Cc: devicetree@...r.kernel.org
>> >> >> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
>> >> >> ---
>> >> >>  .../devicetree/bindings/pinctrl/qcom,sdm845-pinctrl.txt    | 7 ++++++-
>> >> >>  1 file changed, 6 insertions(+), 1 deletion(-)
>> >> >>
>> >> >> diff --git a/Documentation/devicetree/bindings/pinctrl/qcom,sdm845-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/qcom,sdm845-pinctrl.txt
>> >> >> index 665aadb5ea28..a522ca46667d 100644
>> >> >> --- a/Documentation/devicetree/bindings/pinctrl/qcom,sdm845-pinctrl.txt
>> >> >> +++ b/Documentation/devicetree/bindings/pinctrl/qcom,sdm845-pinctrl.txt
>> >> >> @@ -29,6 +29,11 @@ SDM845 platform.
>> >> >>      Definition: must be 2. Specifying the pin number and flags, as defined
>> >> >>                  in <dt-bindings/interrupt-controller/irq.h>
>> >> >>
>> >> >> +- wakeup-parent:
>> >> >> +    Usage: optional
>> >> >> +    Value type: <phandle>
>> >> >> +    Definition: A phandle to the wakeup interrupt controller for the SoC.
>> >> >
>> >> >Is this really necessary? Is there more than one possible wakeup-parent
>> >> >node?
>> >> >
>> >> No.  There is only one but depending on the architecture, the wakeup
>> >> interrupt controller could be different device like PDC on SDM845 or MPM
>> >> on SDM820.
>> >>
>> >> What do you have in mind? Let me know if you have a better idea than
>> >> referencing in DT.
>> >
>> >If there's only one possibility for a given platform, then you can
>> >just use of_find_compatible_node(). I don't think it matters that
>> >different platforms have a different device here. It's not going to be
>> >a large table and you may need to know the differences if there's not
>> >an abstracted interface to it (seems there is in your case).
>> The GPIO irqchip would be in hierarchy with the wakeup-parent
>> irqchip and no device specific functions would be called directly.
>> We could achieve this with compatible strings to the irqchip.
>>
>> >Alternatively, if the PDC/MPM code knows what interrupt controller it
>> >is associated with, then it could setup that relationship and the
>> >interrupt controller code could retrieve that. Maybe the stacked
>> >domain support doesn't work in that direction (I haven't looked at the
>> >irq code much since that was added).
>> >
>> The PDC/MPM do not know about the association.
>
>Neither does the main interrupt controller. The association is part of
>SoC integration. You can describe that association in either direction
>and that is sufficient from a DT standpoint. You've probably picked
>putting this in the GIC(?) based on what works more easily with the
>Linux irqdomain code.
>
>> >However, my main concern is documenting something genericish in a
>> >device specific binding. It looks like Tegra is trying to add the same
>> >thing, so this needs to be documented in a common place. One question
>> >is whether wakeup is the only use or if this should be more generally
>> >a secondary interrupt parent?
>> >
>> Yes, wakeup is the only use of this interrupt parent.
>
>Maybe for you, but I was wondering about this more generally. Should
>we encode what the function (e.g. wakeup) is in the property name or
>have something like aux-interrupt-controller? Maybe some platforms
>have some need for a secondary interrupt-controller which is not
>wakeup. Routing interrupts to other cores perhaps?
>
Rob,

Would like to know your opinion on Stephen's idea. Could you take a look
at this thread again please?

Thanks,
Lina

>> It is powered by
>> an always-on rail and therefore can detect some interrupts that are
>> routed to it even when the GIC is powered off. Though Tegra's
>> implementation of the irqchip is a bit different from QCOM, the idea is
>> generally the same. It would be helpful, if we could make this a
>> generic enough binding.
>>
>> -- Lina
>>