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>

drivers/base/regmap/internal.h

@@ -53,6 +53,10 @@ struct regmap {
 			spinlock_t spinlock;
 			unsigned long spinlock_flags;
 		};
+		struct {
+			raw_spinlock_t raw_spinlock;
+			unsigned long raw_spinlock_flags;
+		};
 	};
 	regmap_lock lock;
 	regmap_unlock unlock;

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) {
+			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;

include/linux/regmap.h

@@ -343,6 +343,7 @@ typedef void (*regmap_unlock)(void *);
  * @ranges: Array of configuration entries for virtual address ranges.
  * @num_ranges: Number of range configuration entries.
  * @use_hwlock: Indicate if a hardware spinlock should be used.
+ * @use_raw_spinlock: Indicate if a raw spinlock should be used.
  * @hwlock_id: Specify the hardware spinlock id.
  * @hwlock_mode: The hardware spinlock mode, should be HWLOCK_IRQSTATE,
  *		 HWLOCK_IRQ or 0.
@@ -402,6 +403,7 @@ struct regmap_config {
 	unsigned int num_ranges;
 
 	bool use_hwlock;
+	bool use_raw_spinlock;
 	unsigned int hwlock_id;
 	unsigned int hwlock_mode;