regmap: teach regmap to use raw spinlocks if requested in the config

Some drivers might access regmap in a context where a raw spinlock is
held. An example is drivers/irqchip/irq-ls-extirq.c, which calls
regmap_update_bits() from struct irq_chip :: irq_set_type, which is a
method called by __irq_set_trigger() under the desc->lock raw spin lock.

Since desc->lock is a raw spin lock and the regmap internal lock for
mmio is a plain spinlock (which can become sleepable on RT), this is an
invalid locking scheme and we get a splat stating that this is a
"[ BUG: Invalid wait context ]".

It seems reasonable for regmap to have an option use a raw spinlock too,
so add that in the config such that drivers can request it.

Suggested-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20210825205041.927788-2-vladimir.oltean@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 30 insertions, 5 deletions

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 297e95be25b3..d8510708ec54 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -523,6 +523,23 @@ __releases(&map->spinlock)
 	spin_unlock_irqrestore(&map->spinlock, map->spinlock_flags);
 }
 
+static void regmap_lock_raw_spinlock(void *__map)
+__acquires(&map->raw_spinlock)
+{
+	struct regmap *map = __map;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&map->raw_spinlock, flags);
+	map->raw_spinlock_flags = flags;
+}
+
+static void regmap_unlock_raw_spinlock(void *__map)
+__releases(&map->raw_spinlock)
+{
+	struct regmap *map = __map;
+	raw_spin_unlock_irqrestore(&map->raw_spinlock, map->raw_spinlock_flags);
+}
+
 static void dev_get_regmap_release(struct device *dev, void *res)
 {
 	/*
@@ -760,11 +777,19 @@ struct regmap *__regmap_init(struct device *dev,
 	} else {
 		if ((bus && bus->fast_io) ||
 		    config->fast_io) {
-			spin_lock_init(&map->spinlock);
-			map->lock = regmap_lock_spinlock;
-			map->unlock = regmap_unlock_spinlock;
-			lockdep_set_class_and_name(&map->spinlock,
-						   lock_key, lock_name);
+			if (config->use_raw_spinlock) {
+				raw_spin_lock_init(&map->raw_spinlock);
+				map->lock = regmap_lock_raw_spinlock;
+				map->unlock = regmap_unlock_raw_spinlock;
+				lockdep_set_class_and_name(&map->raw_spinlock,
+							   lock_key, lock_name);
+			} else {
+				spin_lock_init(&map->spinlock);
+				map->lock = regmap_lock_spinlock;
+				map->unlock = regmap_unlock_spinlock;
+				lockdep_set_class_and_name(&map->spinlock,
+							   lock_key, lock_name);
+			}
 		} else {
 			mutex_init(&map->mutex);
 			map->lock = regmap_lock_mutex;