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

From: Matthias Kaehlcke <mka@chromium.org>
To: Johan Hovold <johan@kernel.org>
Cc: Johan Hovold <johan+linaro@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Felipe Balbi <balbi@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	Konrad Dybcio <konrad.dybcio@somainline.org>,
	Krishna Kurapati <quic_kriskura@quicinc.com>,
	Stephen Boyd <swboyd@chromium.org>,
	Doug Anderson <dianders@chromium.org>,
	Pavankumar Kondeti <quic_pkondeti@quicinc.com>,
	quic_ppratap@quicinc.com, quic_vpulyala@quicinc.com,
	linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] usb: dwc3: qcom: fix runtime PM wakeup
Date: Thu, 4 Aug 2022 09:25:04 -0700	[thread overview]
Message-ID: <Yuvy4CjCgs48nFnM@google.com> (raw)
In-Reply-To: <YuvuJR0ZqSvwMSi1@hovoldconsulting.com>

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!