Loongson-2F-Fixup-of-problems-introduced-by-mfix-loo.patch

From bd4785c942ae10ec13bc8bd287f4805e8709cb1e Mon Sep 17 00:00:00 2001
From: Wu Zhangjin <wuzhangjin@gmail.com>
Date: Fri, 11 Sep 2009 12:52:28 +0800
Subject: [PATCH] Loongson-2F: Fixup of problems introduced by -mfix-loongson2f-jump of binutils 2.20.1

commit 1699e9f1ed3c9a63920bfe26fef22e8dd69a3fdf in tip.

The -mfix-loongson2f-jump option provided by the binutils 2.20.1 have fixed the
Out-of-order Issue of Loongson-2F described in Chapter 15 of "Loongson2F User
Manual"[1,2], but introduced some problems.

The option changes all of the jumping target to "addr & 0xcfffffff" through the
at($1) register, but for the REBOOT address of loongson-2F: 0xbfc00000, this is
totally wrong, so, this patch try to avoid the problem via telling the
assembler not to use at($1) register.

[1] Loongson2F User Manual(Chinese Version)
http://www.loongson.cn/uploadfile/file/200808211
[2] English Version of Chapter 15:
http://groups.google.com.hk/group/loongson-dev/msg/e0d2e220958f10a6?dmode=source

Reported-and-tested-by: Liu Shiwei <liushiwei@gmail.com>
Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>

diff --git a/arch/mips/loongson/common/reset.c b/arch/mips/loongson/common/reset.c
index 9e10d62..8d1985b 100644
--- a/arch/mips/loongson/common/reset.c
+++ b/arch/mips/loongson/common/reset.c
@@ -39,8 +39,18 @@ static void loongson_restart(char *command)
 	/* do preparation for reboot */
 	mach_prepare_reboot();
 
-	/* reboot via jumping to boot base address */
+	/* reboot via jumping to boot base address
+	 *
+	 * ".set noat" and ".set at" are used to ensure the address not broken
+	 * by the -mfix-loongson2f-jump option provided by binutils 2.20.1 and
+	 * higher which try to change the jumping address to "addr &
+	 * 0xcfffffff" via the at($1) register, this is totally wrong for
+	 * 0xbfc00000(LOONGSON_BOOT_BASE).
+	 */
+
+	__asm__ __volatile__(".set noat\n");
 	loongson_reboot();
+	__asm__ __volatile__(".set at\n");
 }
 
 static void loongson_poweroff(void)
-- 
1.7.1.1