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Date:   Wed, 27 Jul 2022 10:31:04 -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>
 <YtHRFcol5uslEel1@google.com>
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On Fri, Jul 15, 2022 at 01:41:57PM -0700, Matthias Kaehlcke wrote:
> 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>

(attempt to 'summarize' and move the discussion from v1 [1] to here)

gregkh> Why not limit this check to a device type like your changelog mentions?

mka> It is not an sc7180 specific issue. It can occur on any platform where the
mka> dwc3 core has supplies that aren't ready when the dwc3-qcom driver probes.
mka>
mka> It won't blow up right away since it requires 'wakeup-source' to be set for
mka> the dwc3 core, which currently is only the case for 'usb@a600000' of the
mka> sc7280 AFAIK (I set it for sc7180 in my tree for testing, which is when I
mka> found the issue this patch intends to address).

krishna> As Mathias pointed out, no issue was seen so far on present QC targets
krishna> as wakeup-source property was added recently and only for SC7180 and
krishna> SC7280. We ran into some issues like wakeup from system suspend in
krishna> host mode wasn't happening although we enabled wakeup-source in SC7180
krishna> that eventually led us to this bug. But, we tried to add debug prints
krishna> to follow the code flow and see that the issue is present on SM8350
krishna> as well : "supplier 88e9000.phy-wrapper not ready" and deferring dwc3
krishna> probe. This doesn't seem to be specific to SC7180.
krishna>
krishna> Since this is seen on multiple platforms, can we go ahead without
krishna> having any platforms specific checks in the code as in V2 version ?

[1] https://lore.kernel.org/all/YtAv1U1VYkhIY1GA@kroah.com/t/#m6714bf1f2309cfe8be92e6c270ef2a99a9b09ac6