linux-kernel - [tip:x86/urgent] x86, setup: When probing memory with e801, use ax/bx as a pair

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Message-ID: <tip-39b68976ac653cfdc7f872a293e8b7928de2dcc6@git.kernel.org>
Date:	Mon, 25 Apr 2011 23:25:02 GMT
From:	"tip-bot for H. Peter Anvin" <hpa@...ux.intel.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, thomas@...3r.de, hpa@...or.com,
	mingo@...hat.com, chris@...muel.org, tglx@...utronix.de,
	hpa@...ux.intel.com
Subject: [tip:x86/urgent] x86, setup: When probing memory with e801, use ax/bx as a pair

Commit-ID:  39b68976ac653cfdc7f872a293e8b7928de2dcc6
Gitweb:     http://git.kernel.org/tip/39b68976ac653cfdc7f872a293e8b7928de2dcc6
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Mon, 25 Apr 2011 14:52:37 -0700
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Mon, 25 Apr 2011 14:52:37 -0700

x86, setup: When probing memory with e801, use ax/bx as a pair

When we use BIOS function e801 to probe memory, we should use ax/bx
(or cx/dx) as a pair, not mix and match.  This was a typo during the
translation from assembly code, and breaks at least one set of
machines in the field (which return cx = dx = 0).

Reported-and-tested-by: Chris Samuel <chris@...muel.org>
Fix-proposed-by: Thomas Meyer <thomas@...3r.de>
Link: http://lkml.kernel.org/r/1303566747.12067.10.camel@localhost.localdomain
---
 arch/x86/boot/memory.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index cae3feb..db75d07 100644
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -91,7 +91,7 @@ static int detect_memory_e801(void)
 	if (oreg.ax > 15*1024) {
 		return -1;	/* Bogus! */
 	} else if (oreg.ax == 15*1024) {
-		boot_params.alt_mem_k = (oreg.dx << 6) + oreg.ax;
+		boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
 	} else {
 		/*
 		 * This ignores memory above 16MB if we have a memory
--
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