linux-kernel - Re: [PATCH 4/8] usb: dwc3: qcom: fix runtime PM wakeup

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Date:   Thu, 4 Aug 2022 09:25:04 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        quic_ppratap@...cinc.com, quic_vpulyala@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] usb: dwc3: qcom: fix runtime PM wakeup

On Thu, Aug 04, 2022 at 06:04:53PM +0200, Johan Hovold wrote:
> On Thu, Aug 04, 2022 at 08:35:10AM -0700, Matthias Kaehlcke wrote:
> > On Thu, Aug 04, 2022 at 09:35:16AM +0200, Johan Hovold wrote:
> 
> > After enabling runtime suspend for the dwc3 core, dwc3 glue and the xHCI
> > the dwc3-qcom enters autosuspend when the delay expires.
> > 
> > > And the controller is resumed in the wakeup-interrupt handler for the
> > > runtime PM case.
> > >
> > > It seems to work ok, and it looks like the driver has supported this
> > > since it was first merged.
> > 
> > With and without your patch dwc3-qcom enters autosuspend and stays there.
> > USB devices like a mouse or a USB to Ethernet adapter keep working while
> > the glue is suspended.
> 
> Are you sure you're looking at the right controller? And that it is
> actually suspended?

Good point! My mind was set on a SC7180 system, which has a single dwc3
controller, but this time I was tinkering on a SC7280 board, which has
two dwc3, and obviously I was looking at the wrong one (－‸ლ)

> If you plug in a keyboard, enable autosuspend for all devices in the
> path (from glue to the keyboard device) and type away, then the
> controller must remain active. Stop typing, and all devices in the chain
> should suspend.

That's what I expected, and now that I'm looking at the right controller
I'm seeing it. I wondered whether the glue device was somehow special.

> > How is the runtime resume triggered for the dwc3 glue?
> 
> Either by the host driver when it needs to access the device, or by the
> device if it is remote-wakeup capable (e.g. a keyboard, but not
> necessarily a speaker).
> 
> Note that the latter part is what is broken currently as the wakeup
> interrupts were not enabled and those are needed to wake up sc8280xp 
> when the dwc3 glue has been runtime suspended.

Thanks for helping me to get a better understanding!