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

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Message-Id: <200707131619.54898.arnd@arndb.de>
Date:	Fri, 13 Jul 2007 16:19:54 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linuxppc-dev@...abs.org
Cc:	James Bottomley <James.Bottomley@...eleye.com>,
	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	Paul Mackerras <paulus@...ba.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

On Friday 13 July 2007, James Bottomley wrote:
> 
> > IC.
> > 
> >   - flush_kernel_dcache_page() is a no-op on ppc64
> >     (ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE is defined on parisc only).
> > 
> >   - For reference, drivers/scsi/ipr.c (another ppc64 driver) just uses a plain
> >     kmap/memcpy/kunmap sequence
> > 
> > So what should I do?
> 
> Ask someone who knows the architecture ... Anton, Paulus or Benh ... I'm
> fairly certain PPC is VIPT and will need some kind of alias
> resolution ... perhaps its associative enough not to let the aliases be
> a problem.

I'm pretty sure that no ppc64 machine needs alias resolution in the kernel,
although some are VIPT. Last time we discussed this, Segher explained it
to me, but I don't remember which way Cell does it. IIRC, it automatically
flushes cache lines that are accessed through aliases.

It's probably a good idea to have the flush_kernel_dcache_page() in there
anyway, if only to serve as an example for people that copy it into
architecture-independent drivers, same as what we do for the
k{,un}map_atomic() that is also not required on ppc64.

	Arnd <><
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