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

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Message-ID: <Pine.LNX.4.62.0707131541150.18802@pademelon.sonytel.be>
Date:	Fri, 13 Jul 2007 15:45:37 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	James Bottomley <James.Bottomley@...elEye.com>
cc:	Jens Axboe <jens.axboe@...cle.com>,
	Paul Mackerras <paulus@...ba.org>,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	Geoff Levand <geoffrey.levand@...sony.com>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

On Fri, 13 Jul 2007, James Bottomley wrote:
> On Fri, 2007-07-13 at 15:25 +0200, Geert Uytterhoeven wrote:
> > kmap() just returns page_address() on ppc64, as there's no highmem.
> > kunmap() is a no-op.
> 
> > So technically I could just use page_address() directly, but Christoph
> > wanted
> > me to keep the kmap()/kunmap() sequence because it's considered a good
> > practice.
> 
> The point isn't what kmap and kunmap do ... it's the addresses they
> return.  By and large, a kernel virtual address for a page is different
> from the user virtual address.  If the cache is virtually indexed you
> get different cache lines for the same page ... and that sets you up
> with aliases you need to resolve.  parisc is the same ... our
> kmap/kunmap are nops as well, but our kernel virtual addresses are still
> different from the user virtual ones.

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?

With kind regards,
 
Geert Uytterhoeven
Software Architect

Sony Network and Software Technology Center Europe
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