VIA's Southbridge bug: Latest (pseudo-)patch

From: Axel Thimm (Axel.Thimm@physik.fu-berlin.de)
Date: Sat May 19 2001 - 05:07:21 EDT

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    This are the latest suggestions for handling the VIA Southbridge bug as
    derived from the hardware site www.au-ja.de (Many thanks to doelf).

    Could a linux kernel specialist review and form this pseudo-patch to a real
    kernel patch? Given the "old" patch found in 2.4.4 I could have written the
    part of setting the PCI registers, but I am totally in the dark as to how to
    identify EPOX Mobos and derive their BIOS ID.

    Here comes the pseudo-patch:

    if( KT133A || KT133 || KX133 ) {
      if( Mainboard=="Epox 8KTA-3(+)" && BIOS>="8kt31417" )
        return 0; /* EPOX already fixed it their way. */
    #ifdef NEW_PATCH
      Offset 76: Set bit5=0 and bit4=1 ("every PCI master grand")
    #else /* this is already part of 2.4.4 */
      Offset 70: Set bit1=0 ("PCI Delay Transaction = 0")
      Offset 70: Set bit2=0 ("PCI Master Read Caching = 0")
      Offset 75: Set bit0-4 ("0 <= PCI Latency <= 32")
    #endif
    }

    History (condensed version, more found in [1]):
    - When doelf and his colleagues found the Southbridge bug, they already worked
      on a solution, which was adopted by most BIOS updates (but not EPOX) and
      also found its way in 2.4.3-ac7. This patch helped in the majority of the
      buggy boards, but still left some cases unresolved.
    - VIA released their own patch ten days ago which tries to solve the Bug
      (viapfd100.exe and the latest 4in1 driver). Not only is this patch only for
      Windows and undocumented, but it also only applies if the running box has a
      Soundblaster card.
    - Someone analysed the patch and found the changed PCI settings so that the
      patch could be implemented also for systems without a Soundblaster
      card (see [1]). This is the NEW_PATCH outlined above. This seems to be
      working (all related hardware sites which had discovered the bug are content
      now), so it would be nice to have it in the kernel and test it from within
      linux.

    [1] latest english information on the VIA Southbridge bug:
        http://www.au-ja.de/review-kt133a-1-en.html 

    -- 
Axel.Thimm@physik.fu-berlin.de
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