[PATCH RFC] dwc2: Don't assume URB transfer_buffer are dword-aligned

[Michael Zoran]

On Fri, 2017-03-17 at 10:24 +0900, Greg Kroah-Hartman wrote:
> On Thu, Mar 16, 2017 at 09:08:40PM -0300, Mauro Carvalho Chehab
> wrote:
> > The dwc2 hardware doesn't like to do DMA transfers without
> > aligning data in DWORD. The driver also assumes that, even
> > when there's no DMA, at dwc2_read_packet().
> > 
> > That cause buffer overflows, preventing some drivers to work.
> 
> Why aren't the drivers being fixed?  This is a well-known (hopefully)
> restriction on USB data buffers, can't the uvc_driver be fixed?
> 
> > In the specific case of uvc_driver, it uses an array where
> > it caches the content of video controls, passing it to the
> > USB stack via usb_control_msg(). Typical controls use 1 or 2
> > bytes. The net result is that other values of the buffer
> > gets overriden when this function is called.
> 
> Not good, it should be fixed, otherwise you are going to have to try
> to

Silly question this being an RFC an all. 

But I wonder if this would be best to fix in the core usb subsystem
rather then making an attempt to fix each and every driver and host
controller.

Since usb_control_msg is a wrapper that can sleep, it's safe to
allocate some memory in the case the destinate buffer isn't aligned.
Essentially have the usb core handle the copy to a temp buffer and copy
it back after the transaction is over.