linux-kernel - [PATCH 1/2] regmap: teach regmap to use raw spinlocks if requested in the config

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Date:   Wed, 25 Aug 2021 23:50:40 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Lee Jones <lee.jones@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Hou Zhiqiang <Zhiqiang.Hou@....com>,
        Biwen Li <biwen.li@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] 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@...nel.org>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/base/regmap/internal.h |  4 ++++
 drivers/base/regmap/regmap.c   | 35 +++++++++++++++++++++++++++++-----
 include/linux/regmap.h         |  2 ++
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 0097696c31de..b1905916f7af 100644
--- a/drivers/base/regmap/internal.h
+++ b/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;
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index fe3e38dd5324..e7ae477d2fcf 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -533,6 +533,23 @@ __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)
 {
 	/*
@@ -770,11 +787,19 @@ 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;
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index f5f08dd0a116..7a3cda794501 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -344,6 +344,7 @@ 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.
@@ -403,6 +404,7 @@ struct regmap_config {
 	unsigned int num_ranges;
 
 	bool use_hwlock;
+	bool use_raw_spinlock;
 	unsigned int hwlock_id;
 	unsigned int hwlock_mode;
 
-- 
2.25.1