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

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Message-ID: <20100415073501.GY30807@buzzloop.caiaq.de>
Date:	Thu, 15 Apr 2010 09:35:01 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Pedro Ribeiro <pedrib@...il.com>
Cc:	Alan Stern <stern@...land.harvard.edu>, linux-usb@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Greg KH <gregkh@...e.de>,
	alsa-devel@...a-project.org
Subject: Re: USB transfer_buffer allocations on 64bit systems

On Wed, Apr 14, 2010 at 06:21:05PM +0100, Pedro Ribeiro wrote:
> On 14 April 2010 17:36, Daniel Mack <daniel@...aq.de> wrote:
> > No worries - I agree. But unfortunately, I'm out of ideas now, and my
> > initial thoughts about what might cause the trouble were abviously not
> > able to explain the issue. Does anyone see further steps of tracking
> > this issue down?
> >
> > Thanks,
> > Daniel
> >
> 
> Well if this is a dirty / dangerous hack, what about your first patch?
> I've been testing it for days and has given me no problems.

[For those who haven't followed all the discussions - this patch used
 usb_buffer_alloc() instead of kmalloc() in the audio USB driver]

No, Alan is right. As long as we don't know what's going on, it
shouldn't be fixed that way.

There might be an update to all USB drivers to use a special allocation
function in order to avoid DMA bounce buffers for non-64-bit aware host
controllers, but that's certainly a second step. First, the bug that you
see needs attention, and the longer you can reproduce it, the better :)

Daniel
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