Re: [PATCH v4 03/10] of/irq: document properties for wakeup interrupt parent

From: Lina Iyer
Date: Tue Apr 16 2019 - 13:42:44 EST

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@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>> ---
>> 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'