| commit | 613d9c3be382f88563a9f03f6311a0b77e321f8c | |
| author | Jim Howard <jiho@c-zone.net> | |
| Fri, 25 Jul 2003 09:02:34 +0000 (25 02:02 -0700) | ||
| committer | Linus Torvalds <torvalds@home.osdl.org> | |
| Fri, 25 Jul 2003 09:02:34 +0000 (25 02:02 -0700) | ||
| tree | eeb5d14a8a4118583fc2e2b575df86a79a075bea | treesnapshot (tar.gz zip) |
| parent | 41bb852b828b5db3a306f934632b69532cae2bdb | commitdiff |
[PATCH] IDE driver VIA support (obscure bug)
This fixes a *very* obscure bug, which only applies to VIA chipsets that
support UDMA-133 mode, and which is only known to be tickled by one
UDMA-66 hard drive (Maxtor 91360U4) that happens to report 80-wire cable
detection opposite to the ATA standard.
The bug appears in a test to see how the BIOS set up UDMA timing. This
test is only reached when the drive says 80-wire *and* the chipset says
40-wire (which is only known to happen with this drive).
The timing bits that are checked represent clocks T minus 2, i.e., ((N -
2) * T). But Vojtech forgot to subtract 2, and applied N = 8 rather
than N = 6 in the test. Since the test masks the bits at 7, they are
always less than 8, and the test always succeeds, even though the BIOS
set UDMA-33.
This fixes a *very* obscure bug, which only applies to VIA chipsets that
support UDMA-133 mode, and which is only known to be tickled by one
UDMA-66 hard drive (Maxtor 91360U4) that happens to report 80-wire cable
detection opposite to the ATA standard.
The bug appears in a test to see how the BIOS set up UDMA timing. This
test is only reached when the drive says 80-wire *and* the chipset says
40-wire (which is only known to happen with this drive).
The timing bits that are checked represent clocks T minus 2, i.e., ((N -
2) * T). But Vojtech forgot to subtract 2, and applied N = 8 rather
than N = 6 in the test. Since the test masks the bits at 7, they are
always less than 8, and the test always succeeds, even though the BIOS
set UDMA-33.
| drivers/ide/pci/via82cxxx.c | diffblobblamehistory |