MIPS: Loongson-2F: Flush the branch target history in BTB and RAS
authorWu Zhangjin <wuzhangjin@gmail.com>
Sat, 13 Mar 2010 04:34:15 +0000 (12:34 +0800)
committerRalf Baechle <ralf@linux-mips.org>
Mon, 12 Apr 2010 16:26:15 +0000 (17:26 +0100)
As per chapter 15 "Errata: Issue of Out-of-order in loongson"[1] to work
around the Loongson 2F erratum we need to do:

"When switching from user mode to kernel mode, you should flush the
branch target history such as BTB and RAS."

[1] 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

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Shinya Kuribayashi <shinya.kuribayashi@necel.com>
Patchwork: http://patchwork.linux-mips.org/patch/1066/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
arch/mips/include/asm/stackframe.h

index 3b6da3330e321772358c9791914e3d472290d2f9..c8419129e77085e7010bab42c4acef99e4aa99e9 100644 (file)
                .endm
 #else
                .macro  get_saved_sp    /* Uniprocessor variation */
+#ifdef CONFIG_CPU_LOONGSON2F
+               /*
+                * Clear BTB (branch target buffer), forbid RAS (return address
+                * stack) to workaround the Out-of-order Issue in Loongson2F
+                * via its diagnostic register.
+                */
+               move    k0, ra
+               jal     1f
+                nop
+1:             jal     1f
+                nop
+1:             jal     1f
+                nop
+1:             jal     1f
+                nop
+1:             move    ra, k0
+               li      k0, 3
+               mtc0    k0, $22
+#endif /* CONFIG_CPU_LOONGSON2F */
 #if defined(CONFIG_32BIT) || defined(KBUILD_64BIT_SYM32)
                lui     k1, %hi(kernelsp)
 #else