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    SubjectRe: MediaGX/GeodeGX1 requires X86_OOSTORE.
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    On Tue, Feb 20, 2007 at 08:34:13PM +0900, takada wrote:
    > I posted with 2.6.20 + enabled X86_OOSTORE.
    > The clflush sze line is in /proc/cpuinfo. but clfush is not in flags line.
    >
    > BTW, can we use WBINVD instruction? I tested compile only.
    > Do you know a method to change dynamically without #ifdef when it works
    > with MediaGX/GeodeGX.
    >
    > diff -Narup a/include/asm-i386/io.h b/include/asm-i386/io.h
    > --- a/include/asm-i386/io.h 2007-02-20 16:23:25.000000000 +0900
    > +++ b/include/asm-i386/io.h 2007-02-20 17:07:14.000000000 +0900
    > @@ -232,7 +232,19 @@ static inline void memcpy_toio(volatile
    > * 2. Accidentally out of order processors (PPro errata #51)
    > */
    >
    > -#if defined(CONFIG_X86_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE)
    > +#ifdef CONFIG_MGEODEGX1
    > +
    > +static inline void dma_flush_cache(void)
    > +{
    > + __asm__ __volatile__ ("wbinvd": : :"memory");
    > +}
    > +
    > +#define dma_cache_inv(_start,_size) dma_flush_cache()
    > +#define dma_cache_wback(_start,_size) dma_flush_cache()
    > +#define dma_cache_wback_inv(_start,_size) dma_flush_cache()
    > +#define flush_write_buffers()
    > +
    > +#elif defined(CONFIG_X86_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE)
    >
    > static inline void flush_write_buffers(void)
    > {
    > -

    Well it is starting to look like it isn't a caching issue, but more
    likely an issue of which order writes are performed in. I think the MAC
    might be seeing the ownership bit change before the rest of the
    descriptor, which shouldn't happen. With X86_OOSTORE, wmb() is called
    between setting the fields in the descriptor and setting the ownership
    bit to the MAC. I still have to investigate a bit more to find out for
    sure, but that could certainly explain why X86_OOSTORE makes the problem
    become much less frequent. It doesn't completely elliminate it though.
    Of course maybe there are two different problems with the same symptoms.

    --
    Len Sorensen
    -
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