Re: [PATCH] usb: dwc2: host: Fix wMaxPacketSize handling (fix webcam regression)

From: Matthias Kaehlcke
Date: Mon Jun 03 2019 - 18:48:11 EST

On Fri, May 31, 2019 at 01:04:12PM -0700, Douglas Anderson wrote:
> In commit abb621844f6a ("usb: ch9: make usb_endpoint_maxp() return
> only packet size") the API to usb_endpoint_maxp() changed. It used to
> just return wMaxPacketSize but after that commit it returned
> wMaxPacketSize with the high bits (the multiplier) masked off. If you
> wanted to get the multiplier it was now up to your code to call the
> new usb_endpoint_maxp_mult() which was introduced in
> commit 541b6fe63023 ("usb: add helper to extract bits 12:11 of
> wMaxPacketSize").
> Prior to the API change most host drivers were updated, but no update
> was made to dwc2. Presumably it was assumed that dwc2 was too
> simplistic to use the multiplier and thus just didn't support a
> certain class of USB devices. However, it turns out that dwc2 did use
> the multiplier and many devices using it were working quite nicely.
> That means that many USB devices have been broken since the API
> change. One such device is a Logitech HD Pro Webcam C920.
> Specifically, though dwc2 didn't directly call usb_endpoint_maxp(), it
> did call usb_maxpacket() which in turn called usb_endpoint_maxp().
> Let's update dwc2 to work properly with the new API.
> Fixes: abb621844f6a ("usb: ch9: make usb_endpoint_maxp() return only packet size")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

I'm not really familiar with the dwc2 driver, but this looks
reasonable to me. FWIW:

Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>