linux-kernel - Re: [PATCH v12 6/6] arm64: dts: qcom: sc7280: Add wakeup-source property for USB node

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Message-ID: <YlBUiBZv6Hhsxn3C@google.com>
Date:   Fri, 8 Apr 2022 08:28:08 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc:     Sandeep Maheswaram <quic_c_sanm@...cinc.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_ppratap@...cinc.com, quic_kriskura@...cinc.com,
        quic_vpulyala@...cinc.com
Subject: Re: [PATCH v12 6/6] arm64: dts: qcom: sc7280: Add wakeup-source
 property for USB node

On Fri, Apr 08, 2022 at 07:32:39AM +0530, Pavan Kondeti wrote:
> On Thu, Apr 07, 2022 at 11:06:40AM -0700, Matthias Kaehlcke wrote:
> > On Thu, Apr 07, 2022 at 02:15:04PM +0530, Sandeep Maheswaram wrote:
> > > Adding wakeup-source property for USB controller in SC7280.
> > > This property is added to inform that the USB controller is
> > > wake up capable and to conditionally power down the phy during
> > > system suspend.
> > > 
> > > Signed-off-by: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
> > > ---
> > >  arch/arm64/boot/dts/qcom/sc7280.dtsi | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/qcom/sc7280.dtsi b/arch/arm64/boot/dts/qcom/sc7280.dtsi
> > > index f0b64be..046262a 100644
> > > --- a/arch/arm64/boot/dts/qcom/sc7280.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/sc7280.dtsi
> > > @@ -2916,6 +2916,7 @@
> > >  				phys = <&usb_1_hsphy>, <&usb_1_ssphy>;
> > >  				phy-names = "usb2-phy", "usb3-phy";
> > >  				maximum-speed = "super-speed";
> > > +				wakeup-source;
> > >  			};
> > >  		};
> > 
> > Not all SC7280 boards may want to enable wakeup from USB, so this is
> > probably best configured on a per-board basis.
> 
> This wakeup capability is provided by the SoC. If a particular
> board does not want to support, ideally it needs to be disabled from
> user space. The capability is always there but some platforms choose to
> disable it.

I guess 'wakeup-source' is a bit of an edge case between hardware capability
(which is certainly required to make wakeup work) and policy.

arch/arm64/boot/dts/mediatek/mt2712-evb.dts and
arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi are two example where
'wakeup-source' is set at the board level for a USB controller.

It's also true that user space can disable wakeup as you said, and a board
could also delete the property in its device tree if desired.

With that I agree that setting 'wakeup-source' at the SoC level provides
more flexibility and is more in line with the DT as hardware description.

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>