Re: [PATCH v2] usb: dwc3: qcom: Provide stubs for dwc3_qcom_read_usb2_speed function

[Johan Hovold <johan@kernel.org>]

On Tue, Aug 02, 2022 at 06:33:36PM +0200, Johan Hovold wrote:
> On Mon, Aug 01, 2022 at 12:30:15PM +0530, Krishna Kurapati wrote:
> > Dwc3 Qcom driver makes use of usb_hub_find_child API in its efforts
> > to get speed of connected devices (HS/LS/FS) and enable interrupts
> > accordingly.
> 
> > usb_hub_find_child API is a part of usb core compiled
> > either into the kernel or as a module (CONFIG_USB= Y or M). In some
> > builds (make randconfig for i386) CONFIG_USB is not enabled and the
> > usb core is not compiled resulting in linking errors.
> 
> Please replace the above with something more succinct. Whether USB core
> is built as a module or not is completely irrelevant. The problem is
> that the qcom dwc3 driver can be built and used without host support. 
> 
> > Provide stubs for dwc3_qcom_read_usb2_speed function to use
> > usb_hub_find_child API only if CONFIG_USB is enabled. Else return
> > USB_SPEED_UNKNOWN.
> 
> The fact that you need to do this is an indication that something is
> wrong with the current implementation. The glue driver shouldn't be
> touching the host driver internal state directly like this.
> 
> As pointed out here:
> 
> 	https://lore.kernel.org/all/20220802151404.1797-4-johan+linaro@kernel.org/
> 
> dwc3_qcom_read_usb2_speed() is indeed broken and currently triggers a
> NULL-pointer dereference when the controller is used in peripheral mode.
> 
> But for now I guess something like this is needed even if we try to
> avoid stubs in implementation files.

This is how I think this should be fixed instead:

	https://lore.kernel.org/all/20220804151001.23612-4-johan+linaro@kernel.org/

and which keeps the ifdeffery minimal. I included the patch in v2 of the
series that addresses the other problems with this code.

Johan