[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>

3 files changed, 24 insertions, 10 deletions

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index a7572cf464bd..69a91bd46115 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -251,6 +251,9 @@ syscall_exit_cont:
         bne-    2f
 1:
 #endif /* CONFIG_44x */
+BEGIN_FTR_SECTION
+        lwarx   r7,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         stwcx.  r0,0,r1                 /* to clear the reservation */
         lwz     r4,_LINK(r1)
         lwz     r5,_CCR(r1)
@@ -717,6 +720,9 @@ restore:
         mtctr   r11
 
         PPC405_ERR77(0,r1)
+BEGIN_FTR_SECTION
+        lwarx   r11,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         stwcx.  r0,0,r1                 /* to clear the reservation */
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
diff --git a/arch/ppc/kernel/entry.S b/arch/ppc/kernel/entry.S
index b19bfef2034d..59e77eb63338 100644
--- a/arch/ppc/kernel/entry.S
+++ b/arch/ppc/kernel/entry.S
@@ -251,6 +251,9 @@ syscall_exit_cont:
         bne-    2f
 1:
 #endif /* CONFIG_44x */
+BEGIN_FTR_SECTION
+        lwarx   r7,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         stwcx.  r0,0,r1                 /* to clear the reservation */
         lwz     r4,_LINK(r1)
         lwz     r5,_CCR(r1)
@@ -713,6 +716,9 @@ restore:
         mtctr   r11
 
         PPC405_ERR77(0,r1)
+BEGIN_FTR_SECTION
+        lwarx   r11,0,r1
+END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
         stwcx.  r0,0,r1                 /* to clear the reservation */
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
diff --git a/include/asm-powerpc/cputable.h b/include/asm-powerpc/cputable.h
index 9d74338e3dec..4525c784dfd0 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 | \