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Date:   Fri, 15 Jul 2022 13:41:57 -0700
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Krishna Kurapati <quic_kriskura@quicinc.com>
Cc:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] usb: dwc3: qcom: Defer dwc3-qcom probe if dwc3 isn't
 probed properly
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References: <1657891312-21748-1-git-send-email-quic_kriskura@quicinc.com>
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On Fri, Jul 15, 2022 at 06:51:52PM +0530, Krishna Kurapati wrote:

> Subject: usb: dwc3: qcom: Defer dwc3-qcom probe if dwc3 isn't probed properly

nit: "isn't probed properly" sounds like a bug or HW issue. In case
you re-spin maybe change it to "hasn't probed yet" or similar.

> On SC7180 devices, it is observed that dwc3 probing is deferred
> because device_links_check_suppliers() finds that '88e3000.phy'
> isn't ready yet.
> 
> As a part of its probe call, dwc3-qcom driver checks if dwc3 core
> is wakeup capable or not. If the dwc3 core is wakeup capable, driver
> configures dwc-qcom's power domain to be always ON. Also it configures
> dp/dm interrupts accordingly to support wakeup from system suspend.
> 
> More info regarding the same can be found at:
> commit d9be8d5c5b03 ("usb: dwc3: qcom: Keep power domain on to retain controller status")
> commit 6895ea55c385 ("usb: dwc3: qcom: Configure wakeup interrupts during suspend")
> 
> In the event, dwc3 probe gets deferred and is processed after dwc3-qcom
> probe, driver ends up reading the wakeup capability of dwc3 core as false
> leading to instability in suspend/resume path.
> 
> To avoid this scenario, ensure dwc3_probe is successful by checking
> if appropriate driver is assigned to it or not after the of_platform_populate
> call. If it isn't then defer dwc3-qcom probe as well.
> 
> Fixes: 649f5c842ba3 ("usb: dwc3: core: Host wake up support from system suspend")
> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>

Reported-by: Matthias Kaehlcke <mka@chromium.org>
Tested-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>

Please make sure to add reviewers of previous versions or other folks you
would like to review your patches in cc. I found v2 accidentally while
looking for something else.