regmap: Check for register readability before checking cache during read

Ensure that we don't return a spurious cache hit for unreadable registers
(eg, with the flat cache which doesn't understand sparseness) by checking
for readability before we do a cache lookup.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230613-b4-regmap-check-readability-before-cache-v1-1-b144c0b01ed9@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 89a7f1c..fad66b3 100644 (file)
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -2897,6 +2897,9 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
        int ret;
        void *context = _regmap_map_get_context(map);
 
+       if (!regmap_readable(map, reg))
+               return -EIO;
+
        if (!map->cache_bypass) {
                ret = regcache_read(map, reg, val);
                if (ret == 0)
@@ -2906,9 +2909,6 @@ static int _regmap_read(struct regmap *map, unsigned int reg,
        if (map->cache_only)
                return -EBUSY;
 
-       if (!regmap_readable(map, reg))
-               return -EIO;
-
        ret = map->reg_read(context, reg, val);
        if (ret == 0) {
                if (regmap_should_log(map))