regmap: Allow devices to specify which registers are accessible

This is currently unused but we need to know which registers exist and
their properties in order to implement diagnostics like register map
dumps and the cache features.

We use callbacks partly because properties can vary at runtime (eg, through
access locks on registers) and partly because big switch statements are a
good compromise between readable code and small data size for providing
information on big register maps.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index cf3565c..2fa55c5 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -37,6 +37,11 @@
 	void *work_buf;     /* Scratch buffer used to format I/O */
 	struct regmap_format format;  /* Buffer format */
 	const struct regmap_bus *bus;
+
+	unsigned int max_register;
+	bool (*writeable_reg)(struct device *dev, unsigned int reg);
+	bool (*readable_reg)(struct device *dev, unsigned int reg);
+	bool (*volatile_reg)(struct device *dev, unsigned int reg);
 };
 
 static void regmap_format_4_12_write(struct regmap *map,
@@ -116,6 +121,10 @@
 	map->format.val_bytes = config->val_bits / 8;
 	map->dev = dev;
 	map->bus = bus;
+	map->max_register = config->max_register;
+	map->writeable_reg = config->writeable_reg;
+	map->readable_reg = config->readable_reg;
+	map->volatile_reg = config->volatile_reg;
 
 	switch (config->reg_bits) {
 	case 4: