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Date:   Tue, 16 Apr 2019 11:42:35 -0600
From:   Lina Iyer <ilina@codeaurora.org>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Marc Zyngier <marc.zyngier@arm.com>, evgreen@chromium.org,
        linux-kernel@vger.kernel.org, rplsssn@codeaurora.org,
        linux-arm-msm@vger.kernel.org, thierry.reding@gmail.com,
        bjorn.andersson@linaro.org, dianders@chromium.org,
        linus.walleij@linaro.org, Rob Herring <robh@kernel.org>
Subject: Re: [PATCH v4 03/10] of/irq: document properties for wakeup
 interrupt parent
Message-ID: <20190416174235.GC16124@codeaurora.org>
References: <20190313211844.29416-1-ilina@codeaurora.org>
 <20190313211844.29416-4-ilina@codeaurora.org>
 <20190318174236.072f0a95@why.wild-wind.fr.eu.org>
 <20190404155838.GD10883@codeaurora.org>
 <155543368899.15276.6065665159846837534@swboyd.mtv.corp.google.com>
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On Tue, Apr 16 2019 at 10:54 -0600, Stephen Boyd wrote:
>Quoting Lina Iyer (2019-04-04 08:58:38)
>> On Mon, Mar 18 2019 at 11:54 -0600, Marc Zyngier wrote:
>> >On Wed, 13 Mar 2019 15:18:37 -0600
>> >Lina Iyer <ilina@codeaurora.org> wrote:
>> >
>> >Please do Cc Rob when posting DT related patches.
>> >
>> >> Some interrupt controllers in a SoC, are always powered on and have a
>> >> select interrupts routed to them, so that they can wakeup the SoC from
>> >> suspend. Add wakeup-parent DT property to refer to these interrupt
>> >> controllers.
>> >>
>> >> If the interrupts routed to the wakeup parent are not sequential, than a
>> >> map needs to exist to associate the same interrupt line on multiple
>> >> interrupt controllers. Providing this map in every driver is cumbersome.
>> >> Let's add this in the device tree and document the properties to map the
>> >> interrupt specifiers
>> >>
>> >> Signed-off-by: Lina Iyer <ilina@codeaurora.org>
>> >> ---
>> >> Changes in v4:
>> >>      - Added this documentation
>> >> ---
>> >>  .../interrupt-controller/interrupts.txt       | 39 +++++++++++++++++++
>> >>  1 file changed, 39 insertions(+)
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt b/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
>> >> index 8a3c40829899..917b598317f5 100644
>> >> --- a/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
>> >> +++ b/Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
>> >> @@ -108,3 +108,42 @@ commonly used:
>> >>                      sensitivity = <7>;
>> >>              };
>> >>      };
>> >> +
>> >> +3) Interrupt wakeup parent
>> >> +--------------------------
>> >> +
>> >> +Some interrupt controllers in a SoC, are always powered on and have a select
>> >> +interrupts routed to them, so that they can wakeup the SoC from suspend. These
>> >> +interrupt controllers do not fall into the category of a parent interrupt
>> >> +controller and can be specified by the "wakeup-parent" property and contain a
>> >> +single phandle referring to the wakeup capable interrupt controller.
>> >> +
>> >> +   Example:
>> >> +    wakeup-parent = <&pdc_intc>;
>> >> +
>> >> +
>> >> +4) Interrupt mapping
>> >> +--------------------
>> >> +
>> >> +Sometimes interrupts may be detected by more than one interrupt controller
>> >> +(depending on which controller is active). The interrupt controllers may not
>> >> +be in hierarchy and therefore the interrupt controller driver is required to
>> >> +establish the relationship between the same interrupt at different interrupt
>> >> +controllers. If these interrupts are not sequential then a map needs to be
>> >> +specified to help identify these interrupts.
>> >> +
>> >> +Mapping the interrupt specifiers in the device tree can be done using the
>> >> +"irqdomain-map" property. The property contains interrupt specifier at the
>> >> +current interrupt controller followed by the interrupt specifier at the mapped
>> >> +interrupt controller.
>> >> +
>> >> +   irqdomain-map = <incoming-interrupt-specifier mapped-interrupt-specifier>
>> >> +
>> >> +The optional properties "irqdomain-map-mask" and "irqdomain-map-pass-thru" may
>> >> +be provided to help interpret the valid bits of the incoming and mapped
>> >> +interrupt specifiers respectively.
>> >> +
>> >> +   Example:
>> >> +    irqdomain-map = <22 0 &intc 36 0>, <24 0 &intc 37 0>;
>> >> +    irqdomain-map-mask = <0xff 0>;
>> >> +    irqdomain-map-pass-thru = <0 0xff>;
>> >
>> >
>> >This doesn't quite explain how the mask and pass-thru properties are
>> >used. I guess that the mask is used to define the 'useful bits' on the
>> >incoming side, but pass-thru puzzles me. In your example, does it mean
>> >that incoming lines map to outgoing interrupt <0 0>?
>> >
>> Sorry about the late reply.
>>
>> How about this to go with the rest of the documentation -
>>
>> In the above example, the input interrupt specifier map-mask <0xff 0> applied
>> on the incoming interrupt specifier of the map <22 0>, <24 0>, returns the
>> input interrupt 22, 24 etc. The second argument being irq type is immaterial
>> from the map and is used from the incoming request instead. The pass-thru
>> specifier parses the output interrupt specifier from the rest of the unparsed
>> argments from the map <&intc 36 0>, <&intc 37 0> etc to return the output
>> interrupt 36, 37 etc.
>>
>>
>
>I see two things going on here. Do both need to happen?
>
>	#1: Specifying wakeup parent phandle
>	#2: Mapping GPIO interrupts to a parent irqdomain
>
>Do we need the method of specifying the wakeup parent if with a dt
>property if we have a way to map irqdomains from one to another? I think
>I may have already said on the list that we must have #1 but now I'm not
>so sure. It looks like we could get away with just looking into the
>irqdomain-map and then pick out the wakeup parent that way.
>
I thought about it. But the wakeup-parent seems to be needed outside the
irqdomain-map to setup the gpiochip's hierarchy. This could be done by
reading the map, but I am not sure if that approach is clean enough.

>The way the bindings are written shows one way to map interrupts between
>domains but I don't know if it lets us differentiate which irqs go from
>which domain to what other domain. It seems that we assume we're looking
>at only the GPIO to wakeup parent irqdomain mapping from the
>irqdomain-map property in this series. If we had a way to do this with
>the irqdomain map then we could avoid needing a special 'wakeup-parent'
>property.
>