linux-kernel - Re: USB mass storage and ARM cache coherency

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Date:	Tue, 02 Feb 2010 15:42:49 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Andreas Mohr <andi@...as.de>
CC:	Oliver Neukum <oliver@...kum.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>, linux-usb@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Greg KH <greg@...ah.com>
Subject: Re: USB mass storage and ARM cache coherency

Andreas Mohr wrote:
> On Tue, Feb 02, 2010 at 01:07:56PM +0100, Oliver Neukum wrote:
> > Am Dienstag, 2. Februar 2010 13:01:12 schrieb Catalin Marinas:
> > > On Tue, 2010-02-02 at 11:48 +0000, Oliver Neukum wrote:
> > > > Am Montag, 1. Februar 2010 18:29:14 schrieb Catalin Marinas:
> > > > Is it correct to limit this to BULK pipes?
> > > 
> > > I'm not entirely sure. The flush_dcache_page() should only be called for
> > > pages that may be mapped into user space (page cache pages). We don't
> > > need this for control buffers. It was my impression that what's coming
> > > from the mass storage layer intended for page cache pages has the
> > > PIPE_BULK type (I may be wrong though).
> > 
> > For storage that is correct. But what about other sources of pages,
> > for example iSCSI?
> 
> Or... usb-audio? I should have verified that it is using bulk endpoints
> (and thus the patch applies to my case).
> usb-audio probably uses isochronous transfers, thus that would be
> an obvious reason why the patch didn't work for me.

snd-usb-audio indeed uses isochronous transfers, but those buffers are
never mapped into user space.  The intermediate vmalloc()ed buffer is,
however, and there was a bugfix for this recently.  Do you have these
patches in your tree?
http://git.kernel.org/?p=linux/kernel/git/tiwai/sound-2.6.git;a=commit;h=3e879d7bac705be4813a0ec9560cbe31db4b269f
http://git.kernel.org/?p=linux/kernel/git/tiwai/sound-2.6.git;a=commit;h=c32d977b8157bf67cdf47729ce7dd054a26eb534


Best regards,
Clemens
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