gpio: remove const modifier from gpiod_get_direction()

PATCH Superseded Alexandre Courbot 3 participants 5 messages Nov 25, 2014 – Nov 28, 2014 GPIO

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Alexandre Courbot

author

2014-11-25 07:20 UTC #0 lore raw

PATCH 1/1 gpio: remove const modifier from gpiod_get_direction()

Although gpiod_get_direction() can be considered side-effect free for consumers, its internals involve setting or clearing bits in the affected GPIO descriptor, for which we need to force-cast the const descriptor parameter. This could lead to incorrect behavior is the compiler decide to optimize here, so remove this const parameter. The intent is to make gpiod_get_direction() private anyway, so it does not really matter.

Reported-by Uwe Kleine-König <[email protected]>

Signed-off-by Alexandre Courbot <[email protected]>

---
 drivers/gpio/gpiolib-sysfs.c  | 2 +-
 drivers/gpio/gpiolib.c        | 8 +++-----
 include/linux/gpio/consumer.h | 2 +-
 3 files changed, 5 insertions(+), 7 deletions(-)

drivers/gpio/gpiolib-sysfs.c +1 -1

index 781fbed00fc3..2ac1800b58bb 100644
@@ -41,7 +41,7 @@ static DEFINE_MUTEX(sysfs_lock);
 static ssize_t gpio_direction_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
-	const struct gpio_desc	*desc = dev_get_drvdata(dev);
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
 	ssize_t			status;
 
 	mutex_lock(&sysfs_lock);

drivers/gpio/gpiolib.c +3 -5

index 5619922ebf44..0b271ef87c09 100644
@@ -148,7 +148,7 @@ static int gpiochip_find_base(int ngpio)
  *
  * This function may sleep if gpiod_cansleep() is true.
  */
-int gpiod_get_direction(const struct gpio_desc *desc)
+int gpiod_get_direction(struct gpio_desc *desc)
 {
 	struct gpio_chip	*chip;
 	unsigned		offset;

@@ -164,13 +164,11 @@ int gpiod_get_direction(const struct gpio_desc *desc)
 	if (status > 0) {
 		/* GPIOF_DIR_IN, or other positive */
 		status = 1;
-		/* FLAG_IS_OUT is just a cache of the result of get_direction(),
-		 * so it does not affect constness per se */
-		clear_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		clear_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	if (status == 0) {
 		/* GPIOF_DIR_OUT */
-		set_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		set_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	return status;
 }

include/linux/gpio/consumer.h +1 -1

index 83c0a61c605d..d54d158ca327 100644
@@ -66,7 +66,7 @@ __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
 			      unsigned int index, enum gpiod_flags flags);
 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc);
 
-int gpiod_get_direction(const struct gpio_desc *desc);
+int gpiod_get_direction(struct gpio_desc *desc);
 int gpiod_direction_input(struct gpio_desc *desc);
 int gpiod_direction_output(struct gpio_desc *desc, int value);
 int gpiod_direction_output_raw(struct gpio_desc *desc, int value);

Signature · 1 line

2.1.3

Uwe Kleine-König

Acked-by on v1 1/1

2014-11-25 08:01 UTC #1 lore raw

Hello Alexandre,

just some minor nitpicking on the commit log:

Quoted 4 lines · Alexandre Courbot

Although gpiod_get_direction() can be considered side-effect free for consumers, its internals involve setting or clearing bits in the affected GPIO descriptor, for which we need to force-cast the const descriptor parameter. This could lead to incorrect behavior is the

s/ is/ if/, and I think s/parameter/variable to non-const/

Quoted 1 line

compiler decide to optimize here, so remove this const parameter. The

s/decide/decides/; s/parameter/attribute/

Quoted 4 lines

intent is to make gpiod_get_direction() private anyway, so it does not really matter.
Reported-by Uwe Kleine-König <[email protected]>

Acked-by Uwe Kleine-König <[email protected]>

Thanks
Uwe

Signature · 6 lines

Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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Alexandre Courbot

author

2014-11-25 08:09 UTC #2 lore raw

Quoted 11 lines · Uwe Kleine-König

Hello Alexandre,
just some minor nitpicking on the commit log:
Quoted 4 lines · Alexandre Courbot
Although gpiod_get_direction() can be considered side-effect free for consumers, its internals involve setting or clearing bits in the affected GPIO descriptor, for which we need to force-cast the const descriptor parameter. This could lead to incorrect behavior is the
s/ is/ if/, and I think s/parameter/variable to non-const/

Quoted 8 lines

Quoted 1 line
compiler decide to optimize here, so remove this const parameter. The
s/decide/decides/; s/parameter/attribute/
Quoted 4 lines
intent is to make gpiod_get_direction() private anyway, so it does not really matter.
Reported-by Uwe Kleine-König <[email protected]>
Acked-by Uwe Kleine-König <[email protected]>

Thanks ; I should have proof-read myself...

Sending a v2 with a fixed log and your Ack so Linus can just pick the patch as-is. --
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Alexandre Courbot

author

2014-11-25 08:16 UTC #3 lore raw

PATCH v2 1/1 gpio: remove const modifier from gpiod_get_direction()

Although gpiod_get_direction() can be considered side-effect free for consumers, its internals involve setting or clearing bits in the affected GPIO descriptor, for which we need to force-cast the const descriptor variable to non-const. This could lead to incorrect behavior if the compiler decides to optimize here, so remove this const attribute. The intent is to make gpiod_get_direction() private anyway, so it does not really matter.

Reported-by Uwe Kleine-König <[email protected]>

Signed-off-by Alexandre Courbot <[email protected]>

Acked-by Uwe Kleine-König <[email protected]>

---
Changes since v1:
- Fixed poor grammar in commit log
- Added Uwe's Ack

 drivers/gpio/gpiolib-sysfs.c  | 2 +-
 drivers/gpio/gpiolib.c        | 8 +++-----
 include/linux/gpio/consumer.h | 2 +-
 3 files changed, 5 insertions(+), 7 deletions(-)

drivers/gpio/gpiolib-sysfs.c +1 -1

index 781fbed00fc3..2ac1800b58bb 100644
@@ -41,7 +41,7 @@ static DEFINE_MUTEX(sysfs_lock);
 static ssize_t gpio_direction_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
-	const struct gpio_desc	*desc = dev_get_drvdata(dev);
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
 	ssize_t			status;
 
 	mutex_lock(&sysfs_lock);

drivers/gpio/gpiolib.c +3 -5

index 5619922ebf44..0b271ef87c09 100644
@@ -148,7 +148,7 @@ static int gpiochip_find_base(int ngpio)
  *
  * This function may sleep if gpiod_cansleep() is true.
  */
-int gpiod_get_direction(const struct gpio_desc *desc)
+int gpiod_get_direction(struct gpio_desc *desc)
 {
 	struct gpio_chip	*chip;
 	unsigned		offset;

@@ -164,13 +164,11 @@ int gpiod_get_direction(const struct gpio_desc *desc)
 	if (status > 0) {
 		/* GPIOF_DIR_IN, or other positive */
 		status = 1;
-		/* FLAG_IS_OUT is just a cache of the result of get_direction(),
-		 * so it does not affect constness per se */
-		clear_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		clear_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	if (status == 0) {
 		/* GPIOF_DIR_OUT */
-		set_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		set_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	return status;
 }

include/linux/gpio/consumer.h +1 -1

index 83c0a61c605d..d54d158ca327 100644
@@ -66,7 +66,7 @@ __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
 			      unsigned int index, enum gpiod_flags flags);
 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc);
 
-int gpiod_get_direction(const struct gpio_desc *desc);
+int gpiod_get_direction(struct gpio_desc *desc);
 int gpiod_direction_input(struct gpio_desc *desc);
 int gpiod_direction_output(struct gpio_desc *desc, int value);
 int gpiod_direction_output_raw(struct gpio_desc *desc, int value);

Signature · 6 lines

2.1.3

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Linus Walleij

2014-11-28 13:44 UTC #4 lore raw

Quoted 8 lines · Alexandre Courbot

Although gpiod_get_direction() can be considered side-effect free for consumers, its internals involve setting or clearing bits in the affected GPIO descriptor, for which we need to force-cast the const descriptor variable to non-const. This could lead to incorrect behavior if the compiler decides to optimize here, so remove this const attribute. The intent is to make gpiod_get_direction() private anyway, so it does not really matter.

Quoted 7 lines

Reported-by Uwe Kleine-König <[email protected]>
Signed-off-by Alexandre Courbot <[email protected]>
Acked-by Uwe Kleine-König <[email protected]>
---
Changes since v1:
- Fixed poor grammar in commit log
- Added Uwe's Ack

Patch applied after crying blood of the quoted-printable encoding of this mail.

Yours,
Linus Walleij
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