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From: jiho@c-zone.net
To: linux-kernel <linux-kernel@vger.kernel.org>
Cc: torvalds@osdl.org, akpm@osdl.org, alan@lxorguk.ukuu.org.uk,
	B.Zolnierkiewicz@elka.pw.edu.pl, vojtech@suse.cz
Subject: [PATCH] 2.6.0-test1 - IDE driver VIA support (obscure bug)
Date: Sun, 20 Jul 2003 14:44:42 -0700	[thread overview]
Message-ID: <3F1B0D4A.8000908@c-zone.net> (raw)

(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
					 */




                 reply	other threads:[~2003-07-20 21:29 UTC|newest]

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