linux-kernel - [tip:x86/reboot] x86, reboot: Drop redundant write of reboot

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Message-ID: <tip-3i0pfh44c1e3jv5lab0cf7sc@git.kernel.org>
Date:	Thu, 21 Jun 2012 08:07:06 -0700
From:	"tip-bot for H. Peter Anvin" <hpa@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	tglx@...utronix.de
Subject: [tip:x86/reboot] x86, reboot: Drop redundant write of reboot_mode

Commit-ID:  2b1b712f050eaf0ac576591281446dc960c0afc5
Gitweb:     http://git.kernel.org/tip/2b1b712f050eaf0ac576591281446dc960c0afc5
Author:     H. Peter Anvin <hpa@...or.com>
AuthorDate: Wed, 20 Jun 2012 21:18:14 -0700
Committer:  H. Peter Anvin <hpa@...or.com>
CommitDate: Wed, 20 Jun 2012 21:18:14 -0700

x86, reboot: Drop redundant write of reboot_mode

We write reboot_mode to BIOS location 0x472 in
native_machine_emergency_restart() (reboot.c:542) already, there is no
need to then write it again in machine_real_restart().

This means nothing gets written there for MRR_APM, but the APM call is
a poweroff call and doesn't use this memory location.

Link: http://lkml.kernel.org/n/tip-3i0pfh44c1e3jv5lab0cf7sc@git.kernel.org
Signed-off-by: H. Peter Anvin <hpa@...or.com>
---
 arch/x86/kernel/reboot.c |    8 --------
 1 files changed, 0 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 6ddb9cd..6ef559f 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -179,14 +179,6 @@ void __noreturn machine_real_restart(unsigned int type)
 	write_cr3(real_mode_header->trampoline_pgd);
 #endif
 
-	/*
-	 * Write 0x1234 to absolute memory location 0x472.  The BIOS reads
-	 * this on booting to tell it to "Bypass memory test (also warm
-	 * boot)".  This seems like a fairly standard thing that gets set by
-	 * REBOOT.COM programs, and the previous reset routine did this
-	 * too. */
-	*((unsigned short *)0x472) = reboot_mode;
-
 	/* Jump to the identity-mapped low memory code */
 #ifdef CONFIG_X86_32
 	asm volatile("jmpl *%0" : :
--
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