Messages in this thread Patch in this message | | | Date | Sun, 20 Jul 2003 14:42:31 -0700 | From | jiho@c-zone ... | Subject | [PATCH] 2.4.21 - IDE driver VIA support (obscure bug) |
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(Apoligies if line-wrapping is nuts, I've been confined to Mozilla....)
This patch 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-orig Fri Jun 13 07:51:33 2003 +++ drivers/ide/pci/via82cxxx.c Sun Jul 20 11:38:42 2003 @@ -484,7 +484,7 @@ for (i = 24; i >= 0; i -= 8) if (((u >> i) & 0x10) || (((u >> i) & 0x20) && - (((u >> i) & 7) < 8))) { + (((u >> i) & 7) < 6))) { /* BIOS 80-wire bit or * UDMA w/ < 60ns/cycle */
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