linux-kernel - Re: Allocating buffers for USB transfers (again)

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Date:	Wed, 10 Aug 2011 20:06:48 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Daniel Mack <zonque@...il.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Florian Mickler <florian@...kler.org>,
	Oliver Neukum <oliver@...kum.org>, linux-usb@...r.kernel.org,
	alsa-devel@...a-project.org, Clemens Ladisch <clemens@...isch.de>,
	pedrib@...il.com, William Light <wrl@...est.net>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	Robert Hancock <hancockrwd@...il.com>
Subject: Re: Allocating buffers for USB transfers (again)

At Wed, 10 Aug 2011 17:33:02 +0200,
Daniel Mack wrote:
> 
> On 08/10/2011 04:32 PM, Alan Stern wrote:
> > Looking at the driver's current code, it appears that your patch
> > does not fix the bug properly.  Using discontiguous regions in the
> > transfer buffer is perfectly okay.  The real problem is later on,
> > where you do:
> >
> > if (send_it) { out->number_of_packets = FRAMES_PER_URB;
> >
> > This should be
> >
> > out->number_of_packets = outframe;
> >
> > The way it is now, the USB stack will try to use data from all the
> > frame descriptors, and the last few will be stale because the loop
> > doesn't set them.
> 
> That's actually true, even though it doesn't seem to cause any trouble.
> I tested everything here of course, and the output URBs return back from
> the USB stack with their length fields zeroed out, which then
> causes the stack to send packets with zero-length fields at the end.
> 
> However, doing it right doesn't harm either. Thanks for spotting.
> 
> Takashi, can you apply this version?

Yep, applied now.  Thanks.


Takashi
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