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    SubjectRe: USB mass storage and ARM cache coherency
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    On Wed, 2010-03-03 at 03:47 +0000, FUJITA Tomonori wrote:
    > On Wed, 03 Mar 2010 10:29:54 +1100
    > Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
    >
    > > On Tue, 2010-03-02 at 17:05 +0000, Catalin Marinas wrote:
    > >
    > > > The viable solutions so far:
    > > >
    > > > 1. Implement a PIO mapping API similar to the DMA API which takes
    > > > care of the D-cache flushing. This means that PIO drivers would
    > > > need to be modified to use an API like pio_kmap()/pio_kunmap()
    > > > before writing to a page cache page.
    > > > 2. Invert the meaning of PG_arch_1 to denote a clean page. This
    > > > means that by default newly allocated page cache pages are
    > > > considered dirty and even if there isn't a call to
    > > > flush_dcache_page(), update_mmu_cache() would flush the D-cache.
    > > > This is the PowerPC approach.
    > >
    > > I don't see the point of a "PIO" API. I would thus vote for 2 :-) Note
    >
    > Yeah, as powerpc and ia64 do, arm can flush D cache and invalidate I
    > cache when inserting a executable page to pte, IIUC. No need for the
    > new API for I/D consistency.

    I can see that IA-64 uses the PG_arch_1 bit to mark a clean page rather
    than dirty (as we did for ARM). The Documentation/cachetlb.txt needs
    updating.

    Thanks.

    --
    Catalin



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