Re: [PATCH 3/8] usb: dwc3: qcom: fix broken non-host-mode suspend

[Matthias Kaehlcke <mka@chromium.org>]

On Tue, Aug 02, 2022 at 05:13:59PM +0200, Johan Hovold wrote:
> A recent commit implementing wakeup support in host mode instead broke
> suspend for peripheral and OTG mode.
> 
> The hack that was added in the suspend path to determine the speed of
> any device connected to the USB2 bus not only accesses internal driver
> data for a child device, but also dereferences a NULL pointer when not
> in host mode and there is no HCD.
> 
> As the controller can switch role at any time when in OTG mode, there's
> no quick fix to this, and since reverting would leave us with broken
> suspend in host-mode (wakeup triggers immediately), keep the hack for
> now and only fix the NULL-pointer dereference.
> 
> Fixes: 6895ea55c385 ("usb: dwc3: qcom: Configure wakeup interrupts during suspend")
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index be2e3dd36440..b75ff40f75a2 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -301,8 +301,17 @@ static void dwc3_qcom_interconnect_exit(struct dwc3_qcom *qcom)
>  static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
>  {
>  	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> -	struct usb_hcd *hcd = platform_get_drvdata(dwc->xhci);
>  	struct usb_device *udev;
> +	struct usb_hcd *hcd;
> +
> +	if (qcom->mode != USB_DR_MODE_HOST)
> +		return USB_SPEED_UNKNOWN;

Couldn't instead the below block in dwc3_qcom_suspend() be conditional on
the controller being in host mode?

	if (device_may_wakeup(qcom->dev)) {
		qcom->usb2_speed = dwc3_qcom_read_usb2_speed(qcom);
		dwc3_qcom_enable_interrupts(qcom);
	}

I see, the problem is that the role switch could happen at any time as the
commit message says. With this patch there is also a race though, the role
switch could happen just after the check and before obtaining 'hcd'.