regmap: rework ->max_register handling

When regmap consists of single register, 'regmap' subsystem is unable to
understand whether ->max_register is set or not, because in both cases it
is equal to zero. It leads to that the logic based on value of
->max_register doesn't work. For example using of REGCACHE_FLAT fails.

This patch introduces an extra parameter to regmap config, indicating
that zero value in ->max_register is authentic.

Signed-off-by: Jan Dakinevich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/base/regmap/internal.h

···
 #endif
 
 	unsigned int max_register;
+	bool max_register_is_set;
 	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);

drivers/base/regmap/regcache-flat.c

···
 	int i;
 	unsigned int *cache;
 
-	if (!map || map->reg_stride_order < 0 || !map->max_register)
+	if (!map || map->reg_stride_order < 0 || !map->max_register_is_set)
 		return -EINVAL;
 
 	map->cache = kcalloc(regcache_flat_get_index(map, map->max_register)

drivers/base/regmap/regcache.c

···
 			return 0;
 	}
 
-	if (!map->max_register && map->num_reg_defaults_raw)
+	if (!map->max_register_is_set && map->num_reg_defaults_raw) {
 		map->max_register = (map->num_reg_defaults_raw  - 1) * map->reg_stride;
+		map->max_register_is_set = true;
+	}
 
 	if (map->cache_ops->init) {
 		dev_dbg(map->dev, "Initializing %s cache\n",

drivers/base/regmap/regmap.c

···
 
 bool regmap_writeable(struct regmap *map, unsigned int reg)
 {
-	if (map->max_register && reg > map->max_register)
+	if (map->max_register_is_set && reg > map->max_register)
 		return false;
 
 	if (map->writeable_reg)
···
 	if (!map->cache_ops)
 		return false;
 
-	if (map->max_register && reg > map->max_register)
+	if (map->max_register_is_set && reg > map->max_register)
 		return false;
 
 	map->lock(map->lock_arg);
···
 	if (!map->reg_read)
 		return false;
 
-	if (map->max_register && reg > map->max_register)
+	if (map->max_register_is_set && reg > map->max_register)
 		return false;
 
 	if (map->format.format_write)
···
 	map->bus = bus;
 	map->bus_context = bus_context;
 	map->max_register = config->max_register;
+	map->max_register_is_set = map->max_register ?: config->max_register_is_0;
 	map->wr_table = config->wr_table;
 	map->rd_table = config->rd_table;
 	map->volatile_table = config->volatile_table;
···
 	regmap_debugfs_exit(map);
 
 	map->max_register = config->max_register;
+	map->max_register_is_set = map->max_register ?: config->max_register_is_0;
 	map->writeable_reg = config->writeable_reg;
 	map->readable_reg = config->readable_reg;
 	map->volatile_reg = config->volatile_reg;
···
  */
 int regmap_get_max_register(struct regmap *map)
 {
-	return map->max_register ? map->max_register : -EINVAL;
+	return map->max_register_is_set ? map->max_register : -EINVAL;
 }
 EXPORT_SYMBOL_GPL(regmap_get_max_register);
 

include/linux/regmap.h

···
  * @io_port:	  Support IO port accessors. Makes sense only when MMIO vs. IO port
  *		  access can be distinguished.
  * @max_register: Optional, specifies the maximum valid register address.
+ * @max_register_is_0: Optional, specifies that zero value in @max_register
+ *                     should be taken into account. This is a workaround to
+ *                     apply handling of @max_register for regmap that contains
+ *                     only one register.
  * @wr_table:     Optional, points to a struct regmap_access_table specifying
  *                valid ranges for write access.
  * @rd_table:     As above, for read access.
···
 	bool io_port;
 
 	unsigned int max_register;
+	bool max_register_is_0;
 	const struct regmap_access_table *wr_table;
 	const struct regmap_access_table *rd_table;
 	const struct regmap_access_table *volatile_table;