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-rw-r--r--arch/arm/include/asm/cacheflush.h46
1 files changed, 46 insertions, 0 deletions
diff --git a/arch/arm/include/asm/cacheflush.h b/arch/arm/include/asm/cacheflush.h
index 15f2d5bf887..ee753f1749c 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