[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>

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))

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))

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 | \