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

On Fri, 2007-07-13 at 17:10 +0200, Geert Uytterhoeven wrote:

On Fri, 13 Jul 2007, Arnd Bergmann wrote:

quoted

On Friday 13 July 2007, James Bottomley wrote:

quoted

quoted

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!

quoted

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

It's a recent addition to the API ... the previous way of doing it was
flush_dcache_page() but that's expensive and flushes all the user
aliases.  Since you know in this case there are no current user aliases
and you only need to flush the kernel alias, flush_kernel_dcache_page()
was introduced as the cheaper alternative.

James