From f1df323924e2fde14cbcd51209a8cbfc33e0c232 Mon Sep 17 00:00:00 2001 From: Wu Zhangjin Date: Sat, 13 Mar 2010 12:34:15 +0800 Subject: [PATCH] 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 Cc: linux-mips@linux-mips.org Cc: Shinya Kuribayashi Patchwork: http://patchwork.linux-mips.org/patch/1066/ Signed-off-by: Ralf Baechle --- arch/mips/include/asm/stackframe.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h index 3b6da33..c841912 100644 --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -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 -- 2.7.4