1 files changed, 46 insertions, 0 deletions

diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 15f2d5bf8875..ee753f1749cd 100644
--- a/arch/arm/include/asm/cacheflush.h
+++ b/arch/arm/include/asm/cacheflush.h
@@ -435,4 +435,50 @@ static inline void __sync_cache_range_r(volatile void *p, size_t size)
 #define sync_cache_w(ptr) __sync_cache_range_w(ptr, sizeof *(ptr))
 #define sync_cache_r(ptr) __sync_cache_range_r(ptr, sizeof *(ptr))
 
+/*
+ * Disabling cache access for one CPU in an ARMv7 SMP system is tricky.
+ * To do so we must:
+ *
+ * - Clear the SCTLR.C bit to prevent further cache allocations
+ * - Flush the desired level of cache
+ * - Clear the ACTLR "SMP" bit to disable local coherency
+ *
+ * ... and so without any intervening memory access in between those steps,
+ * not even to the stack.
+ *
+ * WARNING -- After this has been called:
+ *
+ * - No ldrex/strex (and similar) instructions must be used.
+ * - The CPU is obviously no longer coherent with the other CPUs.
+ * - This is unlikely to work as expected if Linux is running non-secure.
+ *
+ * Note:
+ *
+ * - This is known to apply to several ARMv7 processor implementations,
+ *   however some exceptions may exist.  Caveat emptor.
+ *
+ * - The clobber list is dictated by the call to v7_flush_dcache_*.
+ *   fp is preserved to the stack explicitly prior disabling the cache
+ *   since adding it to the clobber list is incompatible with having
+ *   CONFIG_FRAME_POINTER=y.  ip is saved as well if ever r12-clobbering
+ *   trampoline are inserted by the linker and to keep sp 64-bit aligned.
+ */
+#define v7_exit_coherency_flush(level) \
+        asm volatile( \
+        "stmfd  sp!, {fp, ip} \n\t" \
+        "mrc    p15, 0, r0, c1, c0, 0   @ get SCTLR \n\t" \
+        "bic    r0, r0, #"__stringify(CR_C)" \n\t" \
+        "mcr    p15, 0, r0, c1, c0, 0   @ set SCTLR \n\t" \
+        "isb    \n\t" \
+        "bl     v7_flush_dcache_"__stringify(level)" \n\t" \
+        "clrex  \n\t" \
+        "mrc    p15, 0, r0, c1, c0, 1   @ get ACTLR \n\t" \
+        "bic    r0, r0, #(1 << 6)       @ disable local coherency \n\t" \
+        "mcr    p15, 0, r0, c1, c0, 1   @ set ACTLR \n\t" \
+        "isb    \n\t" \
+        "dsb    \n\t" \
+        "ldmfd  sp!, {fp, ip}" \
+        : : : "r0","r1","r2","r3","r4","r5","r6","r7", \
+              "r9","r10","lr","memory" )
+
 #endif