On Sat, Aug 06, 2022 at 08:03:11PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Aug 04, 2022 at 05:09:56PM +0200, Johan Hovold wrote:
> > The Qualcomm dwc3 runtime-PM implementation checks the xhci
> > platform-device pointer in the wakeup-interrupt handler to determine
> > whether the controller is in host mode and if so triggers a resume.
> >
> > After a role switch in OTG mode the xhci platform-device would have been
> > freed and the next wakeup from runtime suspend would access the freed
> > memory.
> >
> > Note that role switching is executed from a freezable workqueue, which
> > guarantees that the pointer is stable during suspend.
> >
> > Also note that runtime PM has been broken since commit 2664deb09306
> > ("usb: dwc3: qcom: Honor wakeup enabled/disabled state"), which
> > incidentally also prevents this issue from being triggered.
> >
> > Fixes: a4333c3a6ba9 ("usb: dwc3: Add Qualcomm DWC3 glue driver")
> > Cc: stable@xxxxxxxxxxxxxxx # 4.18
> > Signed-off-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
>
> It'd be good to mention the introduction of dwc3_qcom_is_host() function.
> Initially I thought it is used in a single place, but going through the rest of
> the patches reveals that it is used later on.
I think the helper is warranted on its own as it serves as documentation
of the underlying assumptions that this code relies on.
> > +/* Only usable in contexts where the role can not change. */
> > +static bool dwc3_qcom_is_host(struct dwc3_qcom *qcom)
> > +{
> > + struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> > +
> > + return dwc->xhci;
> > +}
> > +
> > static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
> > {
> > struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> > @@ -460,7 +468,11 @@ static irqreturn_t qcom_dwc3_resume_irq(int irq, void *data)
> > if (qcom->pm_suspended)
> > return IRQ_HANDLED;
> >
> > - if (dwc->xhci)
> > + /*
> > + * This is safe as role switching is done from a freezable workqueue
> > + * and the wakeup interrupts are disabled as part of resume.
> > + */
> > + if (dwc3_qcom_is_host(qcom))
> > pm_runtime_resume(&dwc->xhci->dev);
> >
> > return IRQ_HANDLED;
> > diff --git a/drivers/usb/dwc3/host.c b/drivers/usb/dwc3/host.c
> > index f56c30cf151e..f6f13e7f1ba1 100644
> > --- a/drivers/usb/dwc3/host.c
> > +++ b/drivers/usb/dwc3/host.c
> > @@ -135,4 +135,5 @@ int dwc3_host_init(struct dwc3 *dwc)
> > void dwc3_host_exit(struct dwc3 *dwc)
> > {
> > platform_device_unregister(dwc->xhci);
> > + dwc->xhci = NULL;
> > }
> > --
> > 2.35.1
Johan
