regmap: Add better support for devices without readback support

Currently regmap requires that a reg_read callback is supplied, otherwise a
warning is emitted each time regmap_read() is called. This means a device
or bus without readback support needs to supply dummy reg_read callback.
Apart from that regmap_read() will still work fine if a cache is used.

Remove the warning and let regmap_readable() return false if not reg_read
callback is supplied. This means a device no longer has to supply a dummy
callback if it does not support readback and it also doesn't have to have a
readable_reg callback that always returns false since this is now implicit.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 7111d04f2621..8894b992043e 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -93,6 +93,9 @@ bool regmap_writeable(struct regmap *map, unsigned int reg)
 
 bool regmap_readable(struct regmap *map, unsigned int reg)
 {
+        if (!map->reg_read)
+                return false;
+
         if (map->max_register && reg > map->max_register)
                 return false;
 
@@ -2097,8 +2100,6 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
         int ret;
         void *context = _regmap_map_get_context(map);
 
-        WARN_ON(!map->reg_read);
-
         if (!map->cache_bypass) {
                 ret = regcache_read(map, reg, val);
                 if (ret == 0)