dm: regmap: Implement simple regmap_read & regmap_write

The regmap_read & regmap_write functions were previously declared in
regmap.h but not implemented anywhere. The regmap implementation &
commit message of 6f98b7504f70 ("dm: Add support for register maps
(regmap)") indicate that only memory mapped accesses are supported for
now, so providing simple implementations of regmap_read & regmap_write
is trivial. The access size is presumed to be 4 bytes & endianness is
presumed native, which are the defaults for the regmap code in Linux.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/core/regmap.c

@@ -13,6 +13,8 @@
 #include <mapmem.h>
 #include <regmap.h>
 
+#include <asm/io.h>
+
 DECLARE_GLOBAL_DATA_PTR;
 
 static struct regmap *regmap_alloc_count(int count)
@@ -117,3 +119,21 @@ int regmap_uninit(struct regmap *map)
 
 	return 0;
 }
+
+int regmap_read(struct regmap *map, uint offset, uint *valp)
+{
+	uint32_t *ptr = map_physmem(map->base + offset, 4, MAP_NOCACHE);
+
+	*valp = le32_to_cpu(readl(ptr));
+
+	return 0;
+}
+
+int regmap_write(struct regmap *map, uint offset, uint val)
+{
+	uint32_t *ptr = map_physmem(map->base + offset, 4, MAP_NOCACHE);
+
+	writel(cpu_to_le32(val), ptr);
+
+	return 0;
+}