gpiolib: allow simultaneous setting of multiple GPIO outputs

PATCH In review Rojhalat Ibrahim 3 participants 3 messages Nov 4, 2014 – Nov 14, 2014

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Rojhalat Ibrahim

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2014-11-04 16:12 UTC #0 lore raw

PATCH v6 1/3 gpiolib: allow simultaneous setting of multiple GPIO outputs

Introduce new functions gpiod_set_array & gpiod_set_raw_array to the consumer interface which allow setting multiple outputs with just one function call. Also add an optional set_multiple function to the driver interface. Without an implementation of that function in the chip driver outputs are set sequentially.

Implementing the set_multiple function in a chip driver allows for:
- Improved performance for certain use cases. The original motivation for this was the task of configuring an FPGA. In that specific case, where 9 GPIO lines have to be set many times, configuration time goes down from 48 s to 20 s when using the new function.
- Simultaneous glitch-free setting of multiple pins on any kind of parallel bus attached to GPIOs provided they all reside on the same chip and bank.

Limitations:
Performance is only improved for normal high-low outputs. Open drain and open source outputs are always set separately from each other. Those kinds of outputs could probably be accelerated in a similar way if we could forgo the error checking when setting GPIO directions.

Signed-off-by Rojhalat Ibrahim <[email protected]>

Reviewed-by Alexandre Courbot <[email protected]>

Reviewed-by Mark Brown <[email protected]>

---
Change log:
v6: - rebase on current linux-gpio devel branch
v5: - check can_sleep property per chip
- remove superfluous checks
- supplement documentation
v4: - add gpiod_set_array function for setting logical values
- change interface of the set_multiple driver function to use unsigned long as type for the bit fields
- use generic bitops (which also use unsigned long for bit fields)
- do not use ARCH_NR_GPIOS any more
v3: - add documentation
- change commit message
v2: - use descriptor interface
- allow arbitrary groups of GPIOs spanning multiple chips

 Documentation/gpio/consumer.txt |   27 ++++++
 drivers/gpio/gpiolib.c          |  168 ++++++++++++++++++++++++++++++++++++++++
 include/linux/gpio/consumer.h   |   38 +++++++++
 include/linux/gpio/driver.h     |    4 
 4 files changed, 237 insertions(+)

Documentation/gpio/consumer.txt +27 -0

index 6ce5441..c67f806 100644
@@ -199,6 +199,33 @@ The active-low state of a GPIO can also be queried using the following call:
 Note that these functions should only be used with great moderation ; a driver
 should not have to care about the physical line level.
 
+
+Set multiple GPIO outputs with a single function call
+-----------------------------------------------------
+The following functions set the output values of an array of GPIOs:
+
+	void gpiod_set_array(unsigned int array_size,
+			     struct gpio_desc **desc_array,
+			     int *value_array)
+	void gpiod_set_raw_array(unsigned int array_size,
+				 struct gpio_desc **desc_array,
+				 int *value_array)
+	void gpiod_set_array_cansleep(unsigned int array_size,
+				      struct gpio_desc **desc_array,
+				      int *value_array)
+	void gpiod_set_raw_array_cansleep(unsigned int array_size,
+					  struct gpio_desc **desc_array,
+					  int *value_array)
+
+The array can be an arbitrary set of GPIOs. The functions will try to set
+GPIOs belonging to the same bank or chip simultaneously if supported by the
+corresponding chip driver. In that case a significantly improved performance
+can be expected. If simultaneous setting is not possible the GPIOs will be set
+sequentially.
+Note that for optimal performance GPIOs belonging to the same chip should be
+contiguous within the array of descriptors.
+
+
 GPIOs mapped to IRQs
 --------------------
 GPIO lines can quite often be used as IRQs. You can get the IRQ number

drivers/gpio/gpiolib.c +168 -0

186 lines not on this page · raw message

include/linux/gpio/consumer.h +38 -0

index 12f146f..83c0a61 100644
@@ -74,14 +74,24 @@ int gpiod_direction_output_raw(struct gpio_desc *desc, int value);
 /* Value get/set from non-sleeping context */
 int gpiod_get_value(const struct gpio_desc *desc);
 void gpiod_set_value(struct gpio_desc *desc, int value);
+void gpiod_set_array(unsigned int array_size,
+		     struct gpio_desc **desc_array, int *value_array);
 int gpiod_get_raw_value(const struct gpio_desc *desc);
 void gpiod_set_raw_value(struct gpio_desc *desc, int value);
+void gpiod_set_raw_array(unsigned int array_size,
+			 struct gpio_desc **desc_array, int *value_array);
 
 /* Value get/set from sleeping context */
 int gpiod_get_value_cansleep(const struct gpio_desc *desc);
 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value);
+void gpiod_set_array_cansleep(unsigned int array_size,
+			      struct gpio_desc **desc_array,
+			      int *value_array);
 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc);
 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value);
+void gpiod_set_raw_array_cansleep(unsigned int array_size,
+				  struct gpio_desc **desc_array,
+				  int *value_array);
 
 int gpiod_set_debounce(struct gpio_desc *desc, unsigned debounce);

@@ -210,6 +220,13 @@ static inline void gpiod_set_value(struct gpio_desc *desc, int value)
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }
+static inline void gpiod_set_array(unsigned int array_size,
+				   struct gpio_desc **desc_array,
+				   int *value_array)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
 static inline int gpiod_get_raw_value(const struct gpio_desc *desc)
 {
 	/* GPIO can never have been requested */

@@ -221,6 +238,13 @@ static inline void gpiod_set_raw_value(struct gpio_desc *desc, int value)
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }
+static inline void gpiod_set_raw_array(unsigned int array_size,
+				       struct gpio_desc **desc_array,
+				       int *value_array)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
 
 static inline int gpiod_get_value_cansleep(const struct gpio_desc *desc)
 {

@@ -233,6 +257,13 @@ static inline void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }
+static inline void gpiod_set_array_cansleep(unsigned int array_size,
+					    struct gpio_desc **desc_array,
+					    int *value_array)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
 static inline int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
 {
 	/* GPIO can never have been requested */

@@ -245,6 +276,13 @@ static inline void gpiod_set_raw_value_cansleep(struct gpio_desc *desc,
 	/* GPIO can never have been requested */
 	WARN_ON(1);
 }
+static inline void gpiod_set_raw_array_cansleep(unsigned int array_size,
+						struct gpio_desc **desc_array,
+						int *value_array)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
 
 static inline int gpiod_set_debounce(struct gpio_desc *desc, unsigned debounce)
 {

include/linux/gpio/driver.h +4 -0

index ff200a7..c497c62 100644
@@ -32,6 +32,7 @@ struct seq_file;
  * @get: returns value for signal "offset"; for output signals this
  *	returns either the value actually sensed, or zero
  * @set: assigns output value for signal "offset"
+ * @set_multiple: assigns output values for multiple signals defined by "mask"
  * @set_debounce: optional hook for setting debounce time for specified gpio in
  *      interrupt triggered gpio chips
  * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;

@@ -89,6 +90,9 @@ struct gpio_chip {
 						unsigned offset);
 	void			(*set)(struct gpio_chip *chip,
 						unsigned offset, int value);
+	void			(*set_multiple)(struct gpio_chip *chip,
+						unsigned long *mask,
+						unsigned long *bits);
 	int			(*set_debounce)(struct gpio_chip *chip,
 						unsigned offset,
 						unsigned debounce);

--
2.0.4

Alexandre Courbot

2014-11-07 09:35 UTC #1 lore raw

Quoted 20 lines · Rojhalat Ibrahim

Introduce new functions gpiod_set_array & gpiod_set_raw_array to the consumer interface which allow setting multiple outputs with just one function call. Also add an optional set_multiple function to the driver interface. Without an implementation of that function in the chip driver outputs are set sequentially.
Implementing the set_multiple function in a chip driver allows for:
- Improved performance for certain use cases. The original motivation for this was the task of configuring an FPGA. In that specific case, where 9 GPIO lines have to be set many times, configuration time goes down from 48 s to 20 s when using the new function.
- Simultaneous glitch-free setting of multiple pins on any kind of parallel bus attached to GPIOs provided they all reside on the same chip and bank.
Limitations:
Performance is only improved for normal high-low outputs. Open drain and open source outputs are always set separately from each other. Those kinds of outputs could probably be accelerated in a similar way if we could forgo the error checking when setting GPIO directions.

Quoted 3 lines

Signed-off-by Rojhalat Ibrahim <[email protected]>
Reviewed-by Alexandre Courbot <[email protected]>
Reviewed-by Mark Brown <[email protected]>

Great to see this series pushed until the end! I checked the first two patches again and my approval for them still stands.

Linus Walleij

2014-11-14 09:56 UTC #2 lore raw

In reply to Rojhalat Ibrahim

Quoted 20 lines · Rojhalat Ibrahim

Introduce new functions gpiod_set_array & gpiod_set_raw_array to the consumer interface which allow setting multiple outputs with just one function call. Also add an optional set_multiple function to the driver interface. Without an implementation of that function in the chip driver outputs are set sequentially.
Implementing the set_multiple function in a chip driver allows for:
- Improved performance for certain use cases. The original motivation for this was the task of configuring an FPGA. In that specific case, where 9 GPIO lines have to be set many times, configuration time goes down from 48 s to 20 s when using the new function.
- Simultaneous glitch-free setting of multiple pins on any kind of parallel bus attached to GPIOs provided they all reside on the same chip and bank.
Limitations:
Performance is only improved for normal high-low outputs. Open drain and open source outputs are always set separately from each other. Those kinds of outputs could probably be accelerated in a similar way if we could forgo the error checking when setting GPIO directions.

Quoted 3 lines

Signed-off-by Rojhalat Ibrahim <[email protected]>
Reviewed-by Alexandre Courbot <[email protected]>
Reviewed-by Mark Brown <[email protected]>

OK let's do this.

Patch applied!

Yours,
Linus Walleij