[RFC PATCH 2/2] regmap: Reject fast_io regmap configurations with RBTREE and MAPLE caches

[Guenter Roeck <linux@roeck-us.net>]

REGCACHE_RBTREE and REGCACHE_MAPLE dynamically allocate memory for regmap
operations. This is incompatible with spinlock based locking which is used
for fast_io operations. Reject affected configurations.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
This seems prudent, given that accesses will be protected by spinlock
but may allocate memory with GFP_KERNEL. Another option might be to use
WARN_ON instead of rejecting the configuration to avoid hard regressions
(and I think both drivers/net/ieee802154/mcr20a.c and
sound/soc/codecs/sti-sas.c may be affected, though I can not test it).

 drivers/base/regmap/regmap.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 89a7f1c459c1..b4640285c0b9 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -777,6 +777,15 @@ struct regmap *__regmap_init(struct device *dev,
 	} else {
 		if ((bus && bus->fast_io) ||
 		    config->fast_io) {
+			/*
+			 * fast_io is incompatible with REGCACHE_RBTREE and REGCACHE_MAPLE
+			 * since both need to dynamically allocate memory.
+			 */
+			if (config->cache_type == REGCACHE_RBTREE ||
+			    config->cache_type == REGCACHE_MAPLE) {
+				ret = -EINVAL;
+				goto err_name;
+			}
 			if (config->use_raw_spinlock) {
 				raw_spin_lock_init(&map->raw_spinlock);
 				map->lock = regmap_lock_raw_spinlock;
-- 
2.39.2