[PATCH v2] media: mali-c55: Avoid unaligned access of AEC histogram zone weights

[PATCH v2] media: mali-c55: Avoid unaligned access of AEC histogram zone weights

[David Carlier]

mali_c55_params_aexp_hist_weights() packs the 225 per-zone u8 weights
into the ISP registers four at a time by casting the zone_weights array
to u32 and dereferencing it. The array sits at offset 10 within the
parameter block, so it is only 2-byte aligned and the cast performs an
unaligned 32-bit read.

The Mali-C55 is only found on little-endian ARMv8 systems, where such an
access does not fault, so this is not a functional bug. Copy the four
bytes with memcpy() instead to avoid the unaligned access, which is a
little more efficient and drops the open-coded pointer cast.

No functional change intended.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
v2:
 - Use memcpy() instead of get_unaligned_le32() to copy the weights.
 - Drop the Fixes: tag and Cc: stable; this is a cleanup, not a
   functional fix (the IP is little-endian ARMv8 only, where the
   unaligned access does not fault). Reword the commit message
   accordingly.
 drivers/media/platform/arm/mali-c55/mali-c55-params.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-params.c b/drivers/media/platform/arm/mali-c55/mali-c55-params.c
index de0e9d898..832d8f49b 100644
--- a/drivers/media/platform/arm/mali-c55/mali-c55-params.c
+++ b/drivers/media/platform/arm/mali-c55/mali-c55-params.c
@@ -203,11 +203,11 @@ mali_c55_params_aexp_hist_weights(struct mali_c55 *mali_c55,
 	 * of overwriting other registers.
 	 */
 	for (unsigned int i = 0; i < 56; i++) {
-		val = ((u32 *)params->zone_weights)[i]
-			    & MALI_C55_AEXP_HIST_ZONE_WEIGHT_MASK;
+		memcpy(&val, &params->zone_weights[4 * i], 4);
 		addr = base + MALI_C55_AEXP_HIST_ZONE_WEIGHTS_OFFSET + (4 * i);
 
-		mali_c55_ctx_write(mali_c55, addr, val);
+		mali_c55_ctx_write(mali_c55, addr,
+				   val & MALI_C55_AEXP_HIST_ZONE_WEIGHT_MASK);
 	}
 
 	val = params->zone_weights[MALI_C55_MAX_ZONES - 1];
-- 
2.53.0