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Diffstat (limited to 'arch/arm/include/asm/spinlock.h')
-rw-r--r--arch/arm/include/asm/spinlock.h18
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index da1af524015..fdd3820edff 100644
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -18,7 +18,23 @@
#ifdef CONFIG_THUMB2_KERNEL
#define SEV ALT_SMP("sev.w", "nop.w")
-#define WFE(cond) ALT_SMP("wfe" cond ".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")