Re: [PATCH v2] arm64: dts: qcom: sc7180: Configure USB as wakeup source

[Matthias Kaehlcke <mka@chromium.org>]

Hi Doug,

On Tue, Sep 06, 2022 at 11:33:56AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Thu, Sep 1, 2022 at 10:29 AM Matthias Kaehlcke <mka@chromium.org> wrote:
> >
> > The dwc3 USB controller of the sc7180 supports USB remote
> > wakeup, configure it as a wakeup source.
> >
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> >
> > Changes in v2:
> > - use qcom/arm64-for-6.1 as base, v1 was unintendedly based on a
> >   downstream branch that was used for testing
> >
> >  arch/arm64/boot/dts/qcom/sc7180.dtsi | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/sc7180.dtsi b/arch/arm64/boot/dts/qcom/sc7180.dtsi
> > index e8debb0da411..af5bab27eaf3 100644
> > --- a/arch/arm64/boot/dts/qcom/sc7180.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sc7180.dtsi
> > @@ -2782,6 +2782,8 @@ usb_1: usb@a6f8800 {
> >                                         <&gem_noc MASTER_APPSS_PROC 0 &config_noc SLAVE_USB3 0>;
> >                         interconnect-names = "usb-ddr", "apps-usb";
> >
> > +                       wakeup-source;
> > +
> 
> The patch documenting this property has landed in commit 416b61893860
> ("dt-bindings: usb: qcom,dwc3: add wakeup-source property"). I guess
> the only question is whether this should be in the general sc7180
> device tree file or just for trogdor.

I had a similar comment on the patch for sc7280 [1], there the rationale
for putting the property into the .dtsi of the SoC was that the wakeup
capability is provided by the SoC.

For sc8280xp.dtsi the property is also in the .dtsi of the SoC:

https://git.kernel.org/pub/scm/linux/kernel/git/qcom/linux.git/tree/arch/arm64/boot/dts/qcom/sc8280xp.dtsi?h=arm64-for-6.1#n1315

> Any chance it could cause problems for devices that aren't designed like
> trogdor?

Probably not in a functional sense, however power consumption during system
suspend is slightly higher (2-3 mW) when USB wakeup is enabled. Boards can
disable wakeup by deleting the property in their .dtsi file, though it
is not necessarily evident that this is an option to reduce power
consumption.

[1] https://patchwork.kernel.org/project/linux-arm-msm/patch/1649321104-31322-7-git-send-email-quic_c_sanm@quicinc.com/