[PATCH 3/3] Loongson-2F: Fixup of problems introduced by -mfix-loongson2f-jump of binutils 2.20.1

[Wu Zhangjin <wuzhangjin@gmail.com>]

From: Wu Zhangjin <wuzhangjin@gmail.com>

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>
---
 arch/mips/loongson/common/reset.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/arch/mips/loongson/common/reset.c 
b/arch/mips/loongson/common/reset.c
index 4bd9c18..d5f1a50 100644
--- a/arch/mips/loongson/common/reset.c
+++ b/arch/mips/loongson/common/reset.c
@@ -21,8 +21,18 @@ 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");
        ((void (*)(void))ioremap_nocache(LOONGSON_BOOT_BASE, 4)) ();
+       __asm__ __volatile__(".set at\n");
 }
 
 static void loongson_poweroff(void)
-- 
1.7.0.1