[PATCH 0/2] Workaround for PowerPC 476FP hardware bug

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3 messages, 1 author, 2011-01-26 · open the first message on its own page

[PATCH 0/2] Workaround for PowerPC 476FP hardware bug

From: Dave Kleikamp <hidden>
Date: 2011-01-26 16:23:17

These patches add a workaround to avoid a hang on the DD2 level of the
476FP core.  This hardware bug will be fixed in future products, but this
particular core will used in production.

Dave Kleikamp (2):
  powerpc/476: define specific cpu table entry DD2 core
  powerpc/476: Workaround for PLB6 hang

 arch/powerpc/include/asm/cputable.h |    3 ++-
 arch/powerpc/kernel/cputable.c      |   22 ++++++++++++++++++----
 arch/powerpc/mm/tlb_nohash_low.S    |   35 +++++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 5 deletions(-)

-- 
1.7.3.4

[PATCH 2/2] powerpc/476: Workaround for PLB6 hang

From: Dave Kleikamp <hidden>
Date: 2011-01-26 16:22:57

The 476FP core may hang if an instruction fetch happens during an msync
following a tlbsync.  This workaround makes sure that enough instruction
cache lines are pre-fetched before executing the msync.  (sync and msync
are the same to the compiler.)

Signed-off-by: Dave Kleikamp <redacted>
---
 arch/powerpc/mm/tlb_nohash_low.S |   35 +++++++++++++++++++++++++++++++++++
 1 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/mm/tlb_nohash_low.S b/arch/powerpc/mm/tlb_nohash_low.S
index af405ee..7c63c0e 100644
--- a/arch/powerpc/mm/tlb_nohash_low.S
+++ b/arch/powerpc/mm/tlb_nohash_low.S

@@ -189,6 +189,13 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_47x)
 	blr
 
 #ifdef CONFIG_PPC_47x
+
+/*
+ * 47x variant of icbt
+ */
+# define ICBT(CT,RA,RB)	\
+	.long	0x7c00002c | ((CT) << 21) | ((RA) << 16) | ((RB) << 11)
+
 /*
  * _tlbivax_bcast is only on 47x. We don't bother doing a runtime
  * check though, it will blow up soon enough if we mistakenly try

@@ -206,7 +213,35 @@ _GLOBAL(_tlbivax_bcast)
 	isync
 	eieio
 	tlbsync
+BEGIN_FTR_SECTION
+	b	1f
+END_FTR_SECTION_IFSET(CPU_FTR_476_DD2)
+	sync
+	wrtee	r10
+	blr
+/*
+ * DD2 HW could hang if in instruction fetch happens before msync completes.
+ * Touch enough instruction cache lines to ensure cache hits
+ */
+1:	mflr	r9
+	bl	2f
+2:	mflr	r6
+	li	r7,32
+	ICBT(0,r6,r7)		/* touch next cache line */
+	add	r6,r6,r7
+	ICBT(0,r6,r7)		/* touch next cache line */
+	add	r6,r6,r7
+	ICBT(0,r6,r7)		/* touch next cache line */
 	sync
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	nop
+	mtlr	r9
 	wrtee	r10
 	blr
 #endif /* CONFIG_PPC_47x */

-- 
1.7.3.4

[PATCH 1/2] powerpc/476: define specific cpu table entry DD2 core

From: Dave Kleikamp <hidden>
Date: 2011-01-26 16:26:24

The DD2 core still has some unstability.  Define CPU_FTR_476_DD2 to
enable workarounds in later patches.

This is based on an earlier, unreleased patch for DD1 by Ben Herrenschmidt.

Signed-off-by: Dave Kleikamp <redacted>
---
 arch/powerpc/include/asm/cputable.h |    3 ++-
 arch/powerpc/kernel/cputable.c      |   22 ++++++++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index f0a211d..be3cdf9 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h

@@ -154,6 +154,7 @@ extern const char *powerpc_base_platform;
 #define CPU_FTR_NAP_DISABLE_L2_PR	ASM_CONST(0x0000000000002000)
 #define CPU_FTR_DUAL_PLL_750FX		ASM_CONST(0x0000000000004000)
 #define CPU_FTR_NO_DPM			ASM_CONST(0x0000000000008000)
+#define CPU_FTR_476_DD2			ASM_CONST(0x0000000000010000)
 #define CPU_FTR_NEED_COHERENT		ASM_CONST(0x0000000000020000)
 #define CPU_FTR_NO_BTIC			ASM_CONST(0x0000000000040000)
 #define CPU_FTR_NODSISRALIGN		ASM_CONST(0x0000000000100000)

@@ -465,7 +466,7 @@ enum {
 	    CPU_FTRS_44X | CPU_FTRS_440x6 |
 #endif
 #ifdef CONFIG_PPC_47x
-	    CPU_FTRS_47X |
+	    CPU_FTRS_47X | CPU_FTR_476_DD2 |
 #endif
 #ifdef CONFIG_E200
 	    CPU_FTRS_E200 |

diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 8d74a24..436e1e5 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c

@@ -1811,11 +1811,11 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.machine_check		= machine_check_440A,
 		.platform		= "ppc440",
 	},
-	{ /* 476 core */
-		.pvr_mask		= 0xffff0000,
-		.pvr_value		= 0x11a50000,
+	{ /* 476 DD2 core */
+		.pvr_mask		= 0xffffffff,
+		.pvr_value		= 0x11a52080,
 		.cpu_name		= "476",
-		.cpu_features		= CPU_FTRS_47X,
+		.cpu_features		= CPU_FTRS_47X | CPU_FTR_476_DD2,
 		.cpu_user_features	= COMMON_USER_BOOKE |
 			PPC_FEATURE_HAS_FPU,
 		.mmu_features		= MMU_FTR_TYPE_47x |

@@ -1839,6 +1839,20 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.machine_check		= machine_check_47x,
 		.platform		= "ppc470",
 	},
+	{ /* 476 others */
+		.pvr_mask		= 0xffff0000,
+		.pvr_value		= 0x11a50000,
+		.cpu_name		= "476",
+		.cpu_features		= CPU_FTRS_47X,
+		.cpu_user_features	= COMMON_USER_BOOKE |
+			PPC_FEATURE_HAS_FPU,
+		.mmu_features		= MMU_FTR_TYPE_47x |
+			MMU_FTR_USE_TLBIVAX_BCAST | MMU_FTR_LOCK_BCAST_INVAL,
+		.icache_bsize		= 32,
+		.dcache_bsize		= 128,
+		.machine_check		= machine_check_47x,
+		.platform		= "ppc470",
+	},
 	{	/* default match */
 		.pvr_mask		= 0x00000000,
 		.pvr_value		= 0x00000000,

-- 
1.7.3.4

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