[POWERPC] Avoid unpaired stwcx. on some processors

The context switch code in the kernel issues a dummy stwcx. to clear the
reservation, as recommended by the architecture.  However, some processors
can have issues if this stwcx to address A occurs while the reservation
is already held to a different address B.  To avoid this problem, the dummy
stwcx. needs to be paired with a dummy lwarx to the same address.

This adds the dummy lwarx, and creates a cpu feature bit to indicate
which cpus are affected.  Tested on mpc8641_hpcn_defconfig in
arch/powerpc; build tested in arch/ppc.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 12 insertions, 10 deletions

diff --git a/include/asm-powerpc/cputable.h b/include/asm-powerpc/cputable.h
index 9d74338e3de..4525c784dfd 100644
--- a/include/asm-powerpc/cputable.h
+++ b/include/asm-powerpc/cputable.h
@@ -138,6 +138,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTR_FPU_UNAVAILABLE         ASM_CONST(0x0000000000800000)
 #define CPU_FTR_UNIFIED_ID_CACHE        ASM_CONST(0x0000000001000000)
 #define CPU_FTR_SPE                     ASM_CONST(0x0000000002000000)
+#define CPU_FTR_NEED_PAIRED_STWCX       ASM_CONST(0x0000000004000000)
 
 /*
  * Add the 64-bit processor unique features in the top half of the word;
@@ -261,25 +262,25 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTRS_7450_20        (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7450_21        (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_L3_DISABLE_NAP | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7450_23        (CPU_FTR_COMMON | \
-            CPU_FTR_USE_TB | \
+            CPU_FTR_USE_TB | CPU_FTR_NEED_PAIRED_STWCX | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
 #define CPU_FTRS_7455_1 (CPU_FTR_COMMON | \
-            CPU_FTR_USE_TB | \
+            CPU_FTR_USE_TB | CPU_FTR_NEED_PAIRED_STWCX | \
             CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | CPU_FTR_L3CR | \
             CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | CPU_FTR_HAS_HIGH_BATS | \
             CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
 #define CPU_FTRS_7455_20        (CPU_FTR_COMMON | \
-            CPU_FTR_USE_TB | \
+            CPU_FTR_USE_TB | CPU_FTR_NEED_PAIRED_STWCX | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_L3_DISABLE_NAP | \
@@ -289,31 +290,32 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_HAS_HIGH_BATS | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7447_10        (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_HAS_HIGH_BATS | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_NO_BTIC | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_NO_BTIC | CPU_FTR_PPC_LE | \
+            CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7447   (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_L3CR | CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_HAS_HIGH_BATS | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7447A  (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_HAS_HIGH_BATS | \
-            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE)
+            CPU_FTR_NEED_COHERENT | CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_7448   (CPU_FTR_COMMON | \
             CPU_FTR_USE_TB | \
             CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
             CPU_FTR_HPTE_TABLE | CPU_FTR_SPEC7450 | \
             CPU_FTR_NAP_DISABLE_L2_PR | CPU_FTR_HAS_HIGH_BATS | \
-            CPU_FTR_PPC_LE)
+            CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
 #define CPU_FTRS_82XX   (CPU_FTR_COMMON | \
             CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_USE_TB)
 #define CPU_FTRS_G2_LE  (CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | \