[PATCH 22/22] usb: document that URB transfer_buffer should be aligned

[Laurent Pinchart]

Hi Oliver,

On Thursday 30 Mar 2017 10:11:31 Oliver Neukum wrote:
> Am Donnerstag, den 30.03.2017, 01:15 +0300 schrieb Laurent Pinchart:
> > > +   may also override PAD bytes at the end of the ``transfer_buffer``,
> > > up to the
> > > +   size of the CPU word.
> > 
> > "May" is quite weak here. If some host controller drivers require buffers
> > to be aligned, then it's an API requirement, and all buffers must be
> > aligned. I'm not even sure I would mention that some host drivers require
> > it, I think we should just state that the API requires buffers to be
> > aligned.
> 
> That effectively changes the API. Many network drivers are written with
> the assumption that any contiguous buffer is valid. In fact you could
> argue that those drivers are buggy and must use bounce buffers in those
> cases.
> 
> So we need to include the full story here.

I personally don't care much about whose side is responsible for handling the 
alignment constraints, but I want it to be documented before "fixing" any USB 
driver.

-- 
Regards,

Laurent Pinchart