1 files changed, 41 insertions, 12 deletions

diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index 17eb355707dd..fdd3820edff8 100644
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -5,17 +5,52 @@
 #error SMP not supported on pre-ARMv6 CPUs
 #endif
 
+/*
+ * sev and wfe are ARMv6K extensions.  Uniprocessor ARMv6 may not have the K
+ * extensions, so when running on UP, we have to patch these instructions away.
+ */
+#define ALT_SMP(smp, up)                                        \
+        "9998:  " smp "\n"                                      \
+        "       .pushsection \".alt.smp.init\", \"a\"\n"        \
+        "       .long   9998b\n"                                \
+        "       " up "\n"                                       \
+        "       .popsection\n"
+
+#ifdef CONFIG_THUMB2_KERNEL
+#define SEV             ALT_SMP("sev.w", "nop.w")
+/*
+ * For Thumb-2, special care is needed to ensure that the conditional WFE
+ * instruction really does assemble to exactly 4 bytes (as required by
+ * the SMP_ON_UP fixup code).   By itself "wfene" might cause the
+ * assembler to insert a extra (16-bit) IT instruction, depending on the
+ * presence or absence of neighbouring conditional instructions.
+ *
+ * To avoid this unpredictableness, an approprite IT is inserted explicitly:
+ * the assembler won't change IT instructions which are explicitly present
+ * in the input.
+ */
+#define WFE(cond)       ALT_SMP(                \
+        "it " cond "\n\t"                       \
+        "wfe" cond ".n",                        \
+                                                \
+        "nop.w"                                 \
+)
+#else
+#define SEV             ALT_SMP("sev", "nop")
+#define WFE(cond)       ALT_SMP("wfe" cond, "nop")
+#endif
+
 static inline void dsb_sev(void)
 {
 #if __LINUX_ARM_ARCH__ >= 7
         __asm__ __volatile__ (
                 "dsb\n"
-                "sev"
+                SEV
         );
-#elif defined(CONFIG_CPU_32v6K)
+#else
         __asm__ __volatile__ (
                 "mcr p15, 0, %0, c7, c10, 4\n"
-                "sev"
+                SEV
                 : : "r" (0)
         );
 #endif
@@ -46,9 +81,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
         __asm__ __volatile__(
 "1:     ldrex   %0, [%1]\n"
 "       teq     %0, #0\n"
-#ifdef CONFIG_CPU_32v6K
-"       wfene\n"
-#endif
+        WFE("ne")
 "       strexeq %0, %2, [%1]\n"
 "       teqeq   %0, #0\n"
 "       bne     1b"
@@ -107,9 +140,7 @@ static inline void arch_write_lock(arch_rwlock_t *rw)
         __asm__ __volatile__(
 "1:     ldrex   %0, [%1]\n"
 "       teq     %0, #0\n"
-#ifdef CONFIG_CPU_32v6K
-"       wfene\n"
-#endif
+        WFE("ne")
 "       strexeq %0, %2, [%1]\n"
 "       teq     %0, #0\n"
 "       bne     1b"
@@ -176,9 +207,7 @@ static inline void arch_read_lock(arch_rwlock_t *rw)
 "1:     ldrex   %0, [%2]\n"
 "       adds    %0, %0, #1\n"
 "       strexpl %1, %0, [%2]\n"
-#ifdef CONFIG_CPU_32v6K
-"       wfemi\n"
-#endif
+        WFE("mi")
 "       rsbpls  %0, %1, #0\n"
 "       bmi     1b"
         : "=&r" (tmp), "=&r" (tmp2)