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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Oliver Neukum <oneukum@suse.com>
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Subject: Re: [PATCH 22/22] usb: document that URB transfer_buffer should be aligned
Date: Thu, 30 Mar 2017 12:34:32 +0300
Message-ID: <3181783.rVmBcEVlbi@avalon>
In-Reply-To: <1490861491.8660.2.camel@suse.com>
References: <4f2a7480ba9a3c89e726869fddf17e31cf82b3c7.1490813422.git.mchehab@s-opensource.com> <1822963.cezI9HmAB6@avalon> <1490861491.8660.2.camel@suse.com>
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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