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

Geert Uytterhoeven Geert.Uytterhoeven at sonycom.com
Fri Jul 13 23:45:37 EST 2007

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.


  - 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

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