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    SubjectRe: [PATCH v2] usb: dwc3: qcom: Defer dwc3-qcom probe if dwc3 isn't probed properly
    On Fri, Jul 15, 2022 at 06:51:52PM +0530, Krishna Kurapati wrote:
    > 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>
    > ---
    > v2: Set return value to EPROBE_DEFER to drop reference to dwc3 node
    >
    > drivers/usb/dwc3/dwc3-qcom.c | 3 +++
    > 1 file changed, 3 insertions(+)
    >
    > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
    > index 7703655..6676b39 100644
    > --- a/drivers/usb/dwc3/dwc3-qcom.c
    > +++ b/drivers/usb/dwc3/dwc3-qcom.c
    > @@ -722,6 +722,9 @@ static int dwc3_qcom_of_register_core(struct platform_device *pdev)
    > dev_err(dev, "failed to get dwc3 platform device\n");
    > }
    >
    > + if (!qcom->dwc3->dev.driver)
    > + ret = -EPROBE_DEFER;
    > +
    > node_put:
    > of_node_put(dwc3_np);

    NAK.

    We should not be adding hacks like this to the driver.

    There are other ways to avoid this, but please take a look at the
    following series which makes the problem identified by this patch go
    away first:

    https://lore.kernel.org/all/20220802151404.1797-1-johan+linaro@kernel.org

    Johan

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