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

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Date:   Wed, 15 Jun 2022 01:07:01 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Matthias Kaehlcke <mka@...omium.org>
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>
Subject: Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system
 suspend


On 6/14/2022 11:23 PM, Matthias Kaehlcke wrote:
> On Mon, Jun 13, 2022 at 11:08:32AM -0700, Matthias Kaehlcke wrote:
>> 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.
> It seems device links could be used to make sure the dwc3 core is present:
>
>    Another example for an inconsistent state would be a device link that
>    represents a driver presence dependency, yet is added from the consumer’s
>    ->probe callback while the supplier hasn’t probed yet: Had the driver core
>    known about the device link earlier, it wouldn’t have probed the consumer
>    in the first place. The onus is thus on the consumer to check presence of
>    the supplier after adding the link, and defer probing on non-presence.
>
>    https://www.kernel.org/doc/html/v5.18/driver-api/device_link.html#usage
>
>
> You could add something like this to dwc3_qcom_of_register_core():
>
>
>    device_link_add(dev, &qcom->dwc3->dev,
>    		  DL_FLAG_AUTOREMOVE_CONSUMER | DL_FLAG_AUTOPROBE_CONSUMER);
>
>    if (qcom->dwc3->dev.links.status != DL_DEV_DRIVER_BOUND)
>        ret = -EPROBE_DEFER;
>
>
>  From the doc it isn't clear how the consumer is supposed to check presence
> of the supplier, the above check of the link status is also used in
> drivers/cpufreq/mediatek-cpufreq.c , but not elsewhere outside of the
> driver framework.
Hi Mathias,

     Thanks for the input. I will try the above snippet and confirm if 
probe call happens in sync with of_platform_populate in 
dwc3_qcom_of_register_core

Regards,
Krishna,