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

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Date:   Mon, 13 Jun 2022 11:08:32 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Krishna Kurapati <quic_kriskura@...cinc.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        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>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, quic_pkondeti@...cinc.com,
        quic_ppratap@...cinc.com, quic_vpulyala@...cinc.com,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
Subject: Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from
 system suspend

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.