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

[Lina Iyer]

On Tue, Jan 08 2019 at 07:49 -0700, Rob Herring wrote:
> On Mon, Jan 7, 2019 at 12:51 PM Lina Iyer <ilina@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> > >> Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> > >> ---
> > >>  .../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