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MIPS: Loongson-2F: Flush the branch target history in BTB and RAS 

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>
This commit is contained in:
Wu Zhangjin 2010-03-13 12:34:15 +08:00 committed by Ralf Baechle
parent d814c28cec
commit f1df323924
1 changed files with 19 additions and 0 deletions
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19
arch/mips/include/asm/stackframe.h
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@ -121,6 +121,25 @@
.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