linux/kernel.h: Add PTR_ALIGN_DOWN macro

Add a macro for aligning down a pointer. This is useful to get an
aligned register address when a device allows only word access and
doesn't allow half word or byte access.

Link: https://lore.kernel.org/r/20200722110317.4744-4-kishon@ti.comSigned-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>

include/linux/kernel.h

@@ -34,6 +34,7 @@
 #define ALIGN_DOWN(x, a)	__ALIGN_KERNEL((x) - ((a) - 1), (a))
 #define __ALIGN_MASK(x, mask)	__ALIGN_KERNEL_MASK((x), (mask))
 #define PTR_ALIGN(p, a)		((typeof(p))ALIGN((unsigned long)(p), (a)))
+#define PTR_ALIGN_DOWN(p, a)	((typeof(p))ALIGN_DOWN((unsigned long)(p), (a)))
 #define IS_ALIGNED(x, a)		(((x) & ((typeof(x))(a) - 1)) == 0)
 
 /* generic data direction definitions */