[RFC] JS20 IDE perf patch

[Doug Maxey]

Howdy,

  Have done some investigation of the AMD IDE implementation on the
  JS20 and have come up with a set of patches to address this.  The
  underlying assumption that the PCI bus can only do 66mhz is no
  longer true with the HT implementation on this platform.

  The specific issues seen were:
  1) ide.c has code that assumes the PCI bus only runs between 20 and
     66 mhz.
  2) FW has not completely configured the chipset to run at the higher
     IDE bus speeds.
  3) amd74xx.c does not recognize and cannot use the higher PCI bus
     speeds to enable the higher IDE speeds.

  Item 1 is addressed by creating ATA_PCIMHZ_MIN and ATA_PCIMHZ_MAX in
  linux/ide.h.  These values are used in ide/ide.c and amd74xx.c.  If
  there are arch specific values, they override the the values set in
  linux/ide.h via the arch specific header.

  Item 2 is addressed by fixup_amd_ide in arch/ppc64/kernel/pci.c.

  Item 3 uses the ATA_PCIMHZ* to calculate the PCI bus frequency in
  amd74xx.c and is used to determine the UDMA settings for the
  drives.

  Please review these changes.  Comments are welcome.

++doug

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