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    SubjectRe: [PATCH v7 2/4] usb: dwc3: qcom: Add interconnect support in dwc3 driver
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    Quoting Sandeep Maheswaram (2020-03-31 22:15:43)
    > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
    > index 1dfd024..d33ae86 100644
    > --- a/drivers/usb/dwc3/dwc3-qcom.c
    > +++ b/drivers/usb/dwc3/dwc3-qcom.c
    > @@ -76,8 +85,13 @@ struct dwc3_qcom {
    > enum usb_dr_mode mode;
    > bool is_suspended;
    > bool pm_suspended;
    > + struct icc_path *usb_ddr_icc_path;
    > + struct icc_path *apps_usb_icc_path;
    > };
    >
    > +static int dwc3_qcom_interconnect_enable(struct dwc3_qcom *qcom);
    > +static int dwc3_qcom_interconnect_disable(struct dwc3_qcom *qcom);

    Please get rid of these. We shouldn't need forward declarations.

    > +
    > static inline void dwc3_qcom_setbits(void __iomem *base, u32 offset, u32 val)
    > {
    > u32 reg;
    > @@ -285,6 +307,101 @@ static int dwc3_qcom_resume(struct dwc3_qcom *qcom)
    > return 0;
    > }
    >
    > +
    > +/**
    > + * dwc3_qcom_interconnect_init() - Get interconnect path handles
    > + * @qcom: Pointer to the concerned usb core.
    > + *
    > + */
    > +static int dwc3_qcom_interconnect_init(struct dwc3_qcom *qcom)
    > +{
    > + struct device *dev = qcom->dev;
    > + int ret;
    > +
    > + if (!device_is_bound(&qcom->dwc3->dev))
    > + return -EPROBE_DEFER;

    How is this supposed to work? I see that this was added in an earlier
    revision of this patch series but there isn't any mention of why
    device_is_bound() is used here. It would be great if there was a comment
    detailing why this is necessary. It sounds like maximum_speed is
    important?

    Furthermore, dwc3_qcom_interconnect_init() is called by
    dwc3_qcom_probe() which is the function that registers the device for
    qcom->dwc3->dev. If that device doesn't probe between the time it is
    registered by dwc3_qcom_probe() and this function is called then we'll
    fail dwc3_qcom_probe() with -EPROBE_DEFER. And that will remove the
    qcom->dwc3->dev device from the platform bus because we call
    of_platform_depopulate() on the error path of dwc3_qcom_probe().

    So isn't this whole thing racy and can potentially lead us to a driver
    probe loop where the wrapper (dwc3_qcom) and the core (dwc3) are probing
    and we're trying to time it just right so that driver for dwc3 binds
    before we setup interconnects? I don't know if dwc3 can communicate to
    the wrapper but that would be more of a direct way to do this. Or maybe
    the wrapper should try to read the DT property for maximum speed and
    fallback to a worst case high bandwidth value if it can't figure it out
    itself without help from dwc3 core.

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