[PATCH] 2.4.21 - IDE driver VIA support (obscure bug)

[jiho@c-zone.net]

(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
					 */