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Date: Mon, 16 Jul 2007 15:33:17 +0200
From: Jens Axboe <jens.axboe@oracle.com>
To: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver
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Cc: James Bottomley <James.Bottomley@SteelEye.com>,
	Arnd Bergmann <arnd@arndb.de>, linux-scsi@vger.kernel.org,
	Linux Kernel Development <linux-kernel@vger.kernel.org>,
	Alessandro Rubini <rubini@vision.unipv.it>,
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On Mon, Jul 16 2007, Geert Uytterhoeven wrote:
> On Mon, 16 Jul 2007, Geert Uytterhoeven wrote:
> > On Mon, 16 Jul 2007, 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.
> > 
> > OK, I'll change it to flush_dcache_page().
> 
> Upon closer look, while flush_kernel_dcache_page() is a no-op on ppc64,
> flush_dcache_page() isn't. So I'd prefer to not call it if not really needed.
> 
> And according to James, flush_kernel_dcache_page() should be sufficient...
> 
> So I'm getting puzzled again...

I'll let James expand on why he thinks flush_kernel_dcache_page() should
be sufficient. If the backing is always user memory from
get_user_pages(), then the flush_kernel_dcache_page() looks sufficient.
For the normal IO paths, it could be that or page cache pages too for
instance.

-- 
Jens Axboe