[PATCH 15/28] 8xx: Work around CPU15 erratum.

Scott Wood scottwood at freescale.com
Tue Sep 18 02:57:44 EST 2007

The CPU15 erratum on MPC8xx chips can cause incorrect code execution
under certain circumstances, where there is a conditional or indirect
branch in the last word of a page, with a target in the last cache line
of the next page.  This patch implements one of the suggested
workarounds, by forcing a TLB miss whenever execution crosses a page
boundary.  This is done by invalidating the pages before and after the
one being loaded into the TLB in the ITLB miss handler.

Signed-off-by: Scott Wood <scottwood at freescale.com>
 arch/powerpc/kernel/head_8xx.S     |    6 ++++++
 arch/powerpc/platforms/8xx/Kconfig |   16 ++++++++++++++++
 2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 0ad0d17..1cefa84 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -298,6 +298,12 @@ InstructionTLBMiss:
 	stw	r10, 0(r0)
 	stw	r11, 4(r0)
 	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
+#ifdef CONFIG_8xx_CPU15
+	addi	r11, r10, 0x1000
+	tlbie	r11
+	addi	r11, r10, -0x1000
+	tlbie	r11
 	DO_8xx_CPU6(0x3780, r3)
 	mtspr	SPRN_MD_EPN, r10	/* Have to use MD_EPN for walk, MI_EPN can't */
 	mfspr	r10, SPRN_M_TWB	/* Get level 1 table entry address */
diff --git a/arch/powerpc/platforms/8xx/Kconfig b/arch/powerpc/platforms/8xx/Kconfig
index 8ecd01a..322b155 100644
--- a/arch/powerpc/platforms/8xx/Kconfig
+++ b/arch/powerpc/platforms/8xx/Kconfig
@@ -100,6 +100,22 @@ config 8xx_CPU6
 	  If in doubt, say N here.
+config 8xx_CPU15
+	bool "CPU15 Silicon Errata"
+	default y
+	help
+	  This enables a workaround for erratum CPU15 on MPC8xx chips.
+	  This bug can cause incorrect code execution under certain
+	  circumstances.  This workaround adds some overhead (a TLB miss
+	  every time execution crosses a page boundary), and you may wish
+	  to disable it if you have worked around the bug in the compiler
+	  (by not placing conditional branches or branches to LR or CTR
+	  in the last word of a page, with a target of the last cache
+	  line in the next page), or if you have used some other
+	  workaround.
+	  If in doubt, say Y here.
 	prompt "Microcode patch selection"
 	default NO_UCODE_PATCH

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