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

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Date:	Fri, 13 Jul 2007 17:10:03 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Arnd Bergmann <arnd@...db.de>
cc:	linuxppc-dev@...abs.org,
	James Bottomley <James.Bottomley@...eleye.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 Fri, 13 Jul 2007, Arnd Bergmann wrote:
> 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.

Thanks for confirming!

> 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.

Now my next question: why should I add it, if currently no single driver in
mainline calls flush_kernel_dcache_page()? 

`git grep' finds it in the following files only:
    Documentation/cachetlb.txt
    arch/parisc/kernel/cache.c
    arch/parisc/kernel/pacache.S
    include/asm-parisc/cacheflush.h
    include/linux/highmem.h

With kind regards,
 
Geert Uytterhoeven
Software Architect

Sony Network and Software Technology Center Europe
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