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 08:35:10 -0700	[thread overview]
Message-ID: <YuvnLliIKLK71wx0@google.com> (raw)
In-Reply-To: <Yut2tLqGfu82xcDs@hovoldconsulting.com>

On Thu, Aug 04, 2022 at 09:35:16AM +0200, Johan Hovold wrote:
> On Wed, Aug 03, 2022 at 02:58:33PM -0700, Matthias Kaehlcke wrote:
> > On Tue, Aug 02, 2022 at 05:14:00PM +0200, Johan Hovold wrote:
> > > A device must enable wakeups during runtime suspend regardless of
> > > whether it is capable and allowed to wake the system up from system
> > > suspend.
> > > 
> > > Fixes: 2664deb09306 ("usb: dwc3: qcom: Honor wakeup enabled/disabled state")
> > > Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> > 
> > Ah, I wasn't aware that the same wakeup mechanism is used in runtime suspend.
> > 
> > In how far is runtime PM actually supported/used by this driver? The device is
> > set 'active' in _probe(), and there are no other pm_runtime_* calls, except
> > in dwc3_qcom_remove() and qcom_dwc3_resume_irq(). How does the device get from
> > 'active' into 'suspended'?
> 
> It will be runtime suspended when the child (core) device suspends, but
> you need to enable runtime PM through sysfs first.

Thanks for the clarification.

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.

How is the runtime resume triggered for the dwc3 glue?

Sorry if my questions are very basic, so far I haven't dealt much with
autosuspend and I'm trying to get a better understanding in the context
of the dwc3 and why it is currently broken.