[RFC] regmap: rework ->max_register handling

[Jan Dakinevich]

---- >8 ----
Indeed, it is an ugly workaround, but we need to pass an extra
information to regmap. Another approach I'm thinking about is to
introduce special macro for ->max_register initialization:

    #define REGMAP_MAX_REGISTER_IS_0 UINT_MAX
    #define REGMAP_MAX_REGISTER(_max) ((_max) ?: REGMAP_MAX_REGISTER_IS_0)

and initialize regmap_config in the following way:

    struct regmap_config config = {
        ...
        .max_register = REGMAP_MAX_REGISTER(...),
    };

This will eliminate the need for an extra flag in the config. But this
approach has another disadvantage, it imposes an extra requirement,
that is not satisfied by existing code.
---- >8 ----

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 <jan.dakinevich@xxxxxxxxxxxxxxxxx>
---
 drivers/base/regmap/internal.h      |  1 +
 drivers/base/regmap/regcache-flat.c |  2 +-
 drivers/base/regmap/regcache.c      |  4 +++-
 drivers/base/regmap/regmap.c        | 10 ++++++----
 include/linux/regmap.h              |  5 +++++
 5 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 583dd5d7d46b..bcdb25bec77c 100644
--- a/drivers/base/regmap/internal.h
+++ b/drivers/base/regmap/internal.h
@@ -93,6 +93,7 @@ struct regmap {
 #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);
diff --git a/drivers/base/regmap/regcache-flat.c b/drivers/base/regmap/regcache-flat.c
index b7e4b2464102..9b17c77dec9d 100644
--- a/drivers/base/regmap/regcache-flat.c
+++ b/drivers/base/regmap/regcache-flat.c
@@ -23,7 +23,7 @@ static int regcache_flat_init(struct regmap *map)
 	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)
diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
index ac63a73ccdaa..2e41cb12b8e2 100644
--- a/drivers/base/regmap/regcache.c
+++ b/drivers/base/regmap/regcache.c
@@ -187,8 +187,10 @@ int regcache_init(struct regmap *map, const struct regmap_config *config)
 			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",
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 6db77d8e45f9..5cb425f6f02d 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -89,7 +89,7 @@ EXPORT_SYMBOL_GPL(regmap_check_range_table);
 
 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)
@@ -112,7 +112,7 @@ bool regmap_cached(struct regmap *map, unsigned int 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);
@@ -129,7 +129,7 @@ bool regmap_readable(struct regmap *map, unsigned int reg)
 	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)
@@ -787,6 +787,7 @@ struct regmap *__regmap_init(struct device *dev,
 	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;
@@ -1412,6 +1413,7 @@ int regmap_reinit_cache(struct regmap *map, const struct regmap_config *config)
 	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;
@@ -3383,7 +3385,7 @@ EXPORT_SYMBOL_GPL(regmap_get_val_bytes);
  */
 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);
 
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index c9182a47736e..b743241cfb7c 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -332,6 +332,10 @@ typedef void (*regmap_unlock)(void *);
  * @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.
@@ -422,6 +426,7 @@ struct regmap_config {
 	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;
-- 
2.34.1