ARM: 7450/1: dcache: select DCACHE_WORD_ACCESS for little-endian ARMv6+ CPUs

DCACHE_WORD_ACCESS uses the word-at-a-time API for optimised string
comparisons in the vfs layer.

This patch implements support for load_unaligned_zeropad for ARM CPUs
with native support for unaligned memory accesses (v6+) when running
little-endian.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 41 insertions, 0 deletions

diff --git a/arch/arm/include/asm/word-at-a-time.h b/arch/arm/include/asm/word-at-a-time.h
index 74b2d4578577..4d52f92967a6 100644
--- a/arch/arm/include/asm/word-at-a-time.h
+++ b/arch/arm/include/asm/word-at-a-time.h
@@ -48,6 +48,47 @@ static inline unsigned long find_zero(unsigned long mask)
         return ret;
 }
 
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+
+#define zero_bytemask(mask) (mask)
+
+/*
+ * Load an unaligned word from kernel space.
+ *
+ * In the (very unlikely) case of the word being a page-crosser
+ * and the next page not being mapped, take the exception and
+ * return zeroes in the non-existing part.
+ */
+static inline unsigned long load_unaligned_zeropad(const void *addr)
+{
+        unsigned long ret, offset;
+
+        /* Load word from unaligned pointer addr */
+        asm(
+        "1:     ldr     %0, [%2]\n"
+        "2:\n"
+        "       .pushsection .fixup,\"ax\"\n"
+        "       .align 2\n"
+        "3:     and     %1, %2, #0x3\n"
+        "       bic     %2, %2, #0x3\n"
+        "       ldr     %0, [%2]\n"
+        "       lsl     %1, %1, #0x3\n"
+        "       lsr     %0, %0, %1\n"
+        "       b       2b\n"
+        "       .popsection\n"
+        "       .pushsection __ex_table,\"a\"\n"
+        "       .align  3\n"
+        "       .long   1b, 3b\n"
+        "       .popsection"
+        : "=&r" (ret), "=&r" (offset)
+        : "r" (addr), "Qo" (*(unsigned long *)addr));
+
+        return ret;
+}
+
+
+#endif  /* DCACHE_WORD_ACCESS */
+
 #else   /* __ARMEB__ */
 #include <asm-generic/word-at-a-time.h>
 #endif