regmap: reject volatile update_bits() in cache-only mode

Prevent _regmap_update_bits() from accessing hardware when the register
map is in cache-only mode.

Unlike regmap_raw_read() and _regmap_read(), the volatile
_regmap_update_bits() fast path bypasses the cache_only check. This can
result in unexpected hardware accesses while the device is suspended.

Return -EBUSY to ensure behavior is consistent with other cache-only
access paths.

Signed-off-by: bui duc phuc <phucduc.bui@gmail.com>
Link: https://patch.msgid.link/20260528053204.46783-1-phucduc.bui@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: BuiDucPhuc

drivers/base/regmap/regmap.c

@@ -3257,6 +3257,9 @@ static int _regmap_update_bits(struct regmap *map, unsigned int reg,
 		*change = false;
 
 	if (regmap_volatile(map, reg) && map->reg_update_bits) {
+		if (map->cache_only)
+			return -EBUSY;
+
 		reg = regmap_reg_addr(map, reg);
 		ret = map->reg_update_bits(map->bus_context, reg, mask, val);
 		if (ret == 0 && change)