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Date:   Wed, 9 Jan 2019 10:31:11 -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 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.

>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. 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

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