linux-kernel - Re: [PATCH v2 3/9] usb: dwc3: qcom: fix gadget-only builds

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Message-ID: <Yu6cLSRcSEDZ24lY@hovoldconsulting.com>
Date:   Sat, 6 Aug 2022 18:51:57 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        quic_ppratap@...cinc.com, quic_vpulyala@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 3/9] usb: dwc3: qcom: fix gadget-only builds

On Sat, Aug 06, 2022 at 10:12:50PM +0530, Manivannan Sadhasivam wrote:
> On Sat, Aug 06, 2022 at 06:04:21PM +0200, Johan Hovold wrote:
> > On Sat, Aug 06, 2022 at 07:45:36PM +0530, Manivannan Sadhasivam wrote:
> > > On Thu, Aug 04, 2022 at 05:09:55PM +0200, Johan Hovold wrote:
> > > > A recent change added a dependency to the USB host stack and broke
> > > > gadget-only builds of the driver.
> > > > 
> > > > Fixes: 6895ea55c385 ("usb: dwc3: qcom: Configure wakeup interrupts during suspend")
> > > > Reported-by: Randy Dunlap <rdunlap@...radead.org>
> > > > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> > > > --`-
> > > > 
> > > > Changes in v2
> > > >  - new patch
> > > > 
> > > >  drivers/usb/dwc3/dwc3-qcom.c | 5 ++++-
> > > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> > > > index be2e3dd36440..e9364141661b 100644
> > > > --- a/drivers/usb/dwc3/dwc3-qcom.c
> > > > +++ b/drivers/usb/dwc3/dwc3-qcom.c
> > > > @@ -310,8 +310,11 @@ static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
> > > >  	 * currently supports only 1 port per controller. So
> > > >  	 * this is sufficient.
> > > >  	 */
> > > > +#ifdef CONFIG_USB
> > > >  	udev = usb_hub_find_child(hcd->self.root_hub, 1);
> > > > -
> > > > +#else
> > > > +	udev = NULL;
> > > > +#endif
> > > 
> > > Perhaps the check should be moved to the caller instead? This function still
> > > references "usb_hcd" struct and I don't think that's intended for gadget only
> > > mode.
> > 
> > That wouldn't help with the build failure, which is what this patch is
> > addressing.
> > 
> 
> I should've put it clearly. You should guard the entire function and not just
> usb_hub_find_child(). This way it becomes clear that this whole function depends
> on the USB host functionality. Like,
> 
> #ifdef CONFIG_USB
> static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
> {
> ...
> }
> #elif
> static enum usb_device_speed dwc3_qcom_read_usb2_speed(struct dwc3_qcom *qcom)
> {
> 	return USB_SPEED_UNKNOWN
> }
> #endif

Yeah, that's what Krishna suggested but I wanted to keep the ifdeffery
minimal when fixing the build failure (we generally try to avoid adding
stub functions to implementation files).

Non-host mode was clearly never considered when adding the function in
question as the code blows up otherwise regardless of whether CONFIG_USB
is enabled or not (and a later patch in the series addresses that).

But I'll revisit this too in a couple of weeks.

Thanks for reviewing.

Johan