Exit early if size zero for cache helpers

This patch enables cache helper functions `flush_dcache_range`,
`clean_dcache_range` and `invalidate_dcache_range` to exit early
if the size argument specified is zero

Change-Id: I0b63e8f4bd3d47ec08bf2a0b0b9a7ff8a269a9b0
Signed-off-by: Soby Mathew <soby.mathew@arm.com>

lib/aarch32/cache_helpers.S

@@ -20,6 +20,9 @@
  * This macro can be used for implementing various data cache operations `op`
  */
 .macro do_dcache_maintenance_by_mva op, coproc, opc1, CRn, CRm, opc2
+	/* Exit early if size is zero */
+	cmp	r1, #0
+	beq	exit_loop_\op
 	dcache_line_size r2, r3
 	add	r1, r0, r1
 	sub	r3, r2, #1
@@ -30,6 +33,7 @@ loop_\op:
 	cmp	r0, r1
 	blo	loop_\op
 	dsb	sy
+exit_loop_\op:
 	bx	lr
 .endm
 

lib/aarch64/cache_helpers.S

@@ -20,6 +20,8 @@
  * This macro can be used for implementing various data cache operations `op`
  */
 .macro do_dcache_maintenance_by_mva op
+	/* Exit early if size is zero */
+	cbz	x1, exit_loop_\op
 	dcache_line_size x2, x3
 	add	x1, x0, x1
 	sub	x3, x2, #1
@@ -30,6 +32,7 @@ loop_\op:
 	cmp	x0, x1
 	b.lo    loop_\op
 	dsb	sy
+exit_loop_\op:
 	ret
 .endm
 	/* ------------------------------------------