Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend

From: Matthias Kaehlcke <mka@chromium.org>
To: Krishna Kurapati <quic_kriskura@quicinc.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Rob Herring <robh+dt@kernel.org>, Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Felipe Balbi <balbi@kernel.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Doug Anderson <dianders@chromium.org>,
	Mathias Nyman <mathias.nyman@intel.com>,
	devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, quic_pkondeti@quicinc.com,
	quic_ppratap@quicinc.com, quic_vpulyala@quicinc.com,
	Sandeep Maheswaram <quic_c_sanm@quicinc.com>
Subject: Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend
Date: Mon, 13 Jun 2022 11:08:32 -0700	[thread overview]
Message-ID: <Yqd9IHQEj3Ex+FcF@google.com> (raw)
In-Reply-To: <Yp5nf2w8uVZ38/XZ@google.com>

On Mon, Jun 06, 2022 at 01:45:51PM -0700, Matthias Kaehlcke wrote:
> On Thu, Jun 02, 2022 at 12:35:42PM -0700, Matthias Kaehlcke wrote:
> > Hi Krishna,
> > 
> > with this version I see xHCI errors on my SC7180 based system, like
> > these:
> > 
> > [   65.352605] xhci-hcd xhci-hcd.13.auto: xHC error in resume, USBSTS 0x401, Reinit
> > 
> > [  101.307155] xhci-hcd xhci-hcd.13.auto: WARN: xHC CMD_RUN timeout
> > 
> > After resume a downstream hub isn't enumerated again.
> > 
> > So far I didn't see those with v13, but I aso saw the first error with
> > v16.
> 
> It also happens with v13, but only when a wakeup capable vUSB <= 2
> device is plugged in. Initially I used a wakeup capable USB3 to
> Ethernet adapter to trigger the wakeup case, however older versions
> of this series that use usb_wakeup_enabled_descendants() to check
> for wakeup capable devices didn't actually check for vUSB > 2
> devices.
> 
> So the case were the controller/PHYs is powered down works, but
> the controller is unhappy when the runtime PM path is used during
> system suspend.

The issue isn't seen on all systems using dwc3-qcom and the problem starts
during probe(). The expected probe sequence is something like this:

dwc3_qcom_probe
  dwc3_qcom_of_register_core
    dwc3_probe

  if (device_can_wakeup(&qcom->dwc3->dev))
    ...

The important part is that device_can_wakeup() is called after dwc3_probe()
has completed. That's what I see on a QC SC7280 system, where wakeup is
generally working with these patches.

However on a QC SC7180 system dwc3_probe() is deferred and only executed after
dwc3_qcom_probe(). As a result the device_can_wakeup() call returns false.
With that the controller/driver ends up in an unhappy state after system
suspend.

Probing is deferred on SC7180 because device_links_check_suppliers() finds
that '88e3000.phy' isn't ready yet.