linux-kernel - Applied "regmap: allow to disable all locking mechanisms" to the regmap tree

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Message-Id: <E1eMbhE-00080U-3E@debutante>
Date:   Wed, 06 Dec 2017 15:33:16 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Mark Brown <broonie@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Applied "regmap: allow to disable all locking mechanisms" to the regmap tree

The patch

   regmap: allow to disable all locking mechanisms

has been applied to the regmap tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From c9b41fcf272b4926b373d21c2b83dfe374313780 Mon Sep 17 00:00:00 2001
From: Bartosz Golaszewski <brgl@...ev.pl>
Date: Wed, 6 Dec 2017 15:26:21 +0100
Subject: [PATCH] regmap: allow to disable all locking mechanisms

We have a use case in the at24 EEPROM driver (recently converted to
using regmap instead of raw i2c/smbus calls) where we read from/write
to the regmap in a loop, while protecting the entire loop with
a mutex.

Currently this implicitly makes us use two mutexes - one in the driver
and one in regmap. While browsing the code for similar use cases I
noticed a significant number of places where locking *seems* redundant.

Allow users to completely disable any locking mechanisms in regmap
config.

Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 drivers/base/regmap/regmap.c | 9 ++++++++-
 include/linux/regmap.h       | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 8d516a9bfc01..72917b2fc10e 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -459,6 +459,11 @@ static void regmap_unlock_hwlock_irqrestore(void *__map)
 }
 #endif
 
+static void regmap_lock_unlock_empty(void *__map)
+{
+
+}
+
 static void regmap_lock_mutex(void *__map)
 {
 	struct regmap *map = __map;
@@ -669,7 +674,9 @@ struct regmap *__regmap_init(struct device *dev,
 		goto err;
 	}
 
-	if (config->lock && config->unlock) {
+	if (config->disable_locking) {
+		map->lock = map->unlock = regmap_lock_unlock_empty;
+	} else if (config->lock && config->unlock) {
 		map->lock = config->lock;
 		map->unlock = config->unlock;
 		map->lock_arg = config->lock_arg;
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index 15eddc1353ba..072a90229e34 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -264,6 +264,9 @@ typedef void (*regmap_unlock)(void *);
  *                field is NULL but precious_table (see below) is not, the
  *                check is performed on such table (a register is precious if
  *                it belongs to one of the ranges specified by precious_table).
+ * @disable_locking: This regmap is either protected by external means or
+ *                   is guaranteed not be be accessed from multiple threads.
+ *                   Don't use any locking mechanisms.
  * @lock:	  Optional lock callback (overrides regmap's default lock
  *		  function, based on spinlock or mutex).
  * @unlock:	  As above for unlocking.
@@ -333,6 +336,8 @@ struct regmap_config {
 	bool (*readable_reg)(struct device *dev, unsigned int reg);
 	bool (*volatile_reg)(struct device *dev, unsigned int reg);
 	bool (*precious_reg)(struct device *dev, unsigned int reg);
+
+	bool disable_locking;
 	regmap_lock lock;
 	regmap_unlock unlock;
 	void *lock_arg;
-- 
2.15.0