linux-kernel - Re: USB transfer_buffer allocations on 64bit systems

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Date:	Thu, 8 Apr 2010 12:59:38 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Daniel Mack <daniel@...aq.de>, <linux-kernel@...r.kernel.org>,
	Pedro Ribeiro <pedrib@...il.com>, <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>, <alsa-devel@...a-project.org>,
	<linux-usb@...r.kernel.org>
Subject: Re: USB transfer_buffer allocations on 64bit systems

On Thu, 8 Apr 2010, Oliver Neukum wrote:

> Am Mittwoch, 7. April 2010 17:46:17 schrieb Alan Stern:
> > Or alternatively, instead of allocating regular memory the routine
> > could simply fail.  Then the caller would be responsible for checking
> > and using regular memory instead of dma-consistent memory.  Of course,
> > that would put an even larger burden on the caller than just forcing it
> > to keep track of what flag to use.
> 
> Then it would be sensible to pass it a filled URB, modify it or return
> an error code.

That would work, but it doesn't match the way existing drivers use the
interface.  For example, the audio driver allocates a 16-byte coherent
buffer and then uses four bytes from it for each of four different 
URBs.

Alan Stern

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