linux-kernel - Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

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Message-Id: <1184593643.3447.9.camel@localhost.localdomain>
Date:	Mon, 16 Jul 2007 08:47:23 -0500
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	Arnd Bergmann <arnd@...db.de>, linux-scsi@...r.kernel.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	Linux/PPC Development <linuxppc-dev@...abs.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

On Mon, 2007-07-16 at 14:16 +0200, Jens Axboe wrote:
> On Mon, Jul 16 2007, Geert Uytterhoeven wrote:
> > On Fri, 13 Jul 2007, Geert Uytterhoeven wrote:
> > > Ah, that explains it. flush_dcache_page() is used in some drivers.
> > > I'll update my patches. Thanks for the comments!
> > 
> > Does this look OK?
> >   - Replaced KM_USER0 by KM_IRQ0 (all routines are either called from an
> >     interrupt handler, from .request_fn (ps3disk), or from .queuecommand
> >     (ps3rom))
> 
> That looks good.
> 
> >   - Add a call to flush_kernel_dcache_page() in routines that write to buffers
> 
> Hmm, I would have thought a flush_dcache_page() would be more
> appropriate, the backing could be page cache pages.

No ... that was the point of flush_kernel_dcache_page().  The page in
question is page cache backed and contains user mappings.  However, the
block layer has already done a flush_dcache_page() in get_user_pages()
and the user shouldn't be touching memory under I/O (unless they want
self induced aliasing problems) so we're free to assume all the user
cachelines are purged, hence all we have to do is flush the kernel alias
to bring the page up to date and make the users see it correctly.

James


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