regmap: Add a function to check if a regmap register is cached

Add a function to check if a regmap register is cached. This will be used
in debugfs to dump the cached values of write only registers.
Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/internal.h

@@ -173,6 +173,7 @@ struct regcache_ops {
 	int (*drop)(struct regmap *map, unsigned int min, unsigned int max);
 };
 
+bool regmap_cached(struct regmap *map, unsigned int reg);
 bool regmap_writeable(struct regmap *map, unsigned int reg);
 bool regmap_readable(struct regmap *map, unsigned int reg);
 bool regmap_volatile(struct regmap *map, unsigned int reg);

drivers/base/regmap/regmap.c

@@ -93,6 +93,29 @@ bool regmap_writeable(struct regmap *map, unsigned int reg)
 	return true;
 }
 
+bool regmap_cached(struct regmap *map, unsigned int reg)
+{
+	int ret;
+	unsigned int val;
+
+	if (map->cache == REGCACHE_NONE)
+		return false;
+
+	if (!map->cache_ops)
+		return false;
+
+	if (map->max_register && reg > map->max_register)
+		return false;
+
+	map->lock(map->lock_arg);
+	ret = regcache_read(map, reg, &val);
+	map->unlock(map->lock_arg);
+	if (ret)
+		return false;
+
+	return true;
+}
+
 bool regmap_readable(struct regmap *map, unsigned int reg)
 {
 	if (!map->reg_read)