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:

quoted

kmap() just returns page_address() on ppc64, as there's no highmem.
kunmap() is a no-op.

quoted

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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