[PATCH 1/2] gpio: add pin biasing and drive mode to gpiolib

[Linus Walleij]

From: Linus Walleij <linus.walleij at linaro.org>

This adds two functions for struct gpio_chip chips to provide pin
bias and drive mode settings for individual pins. Implementers does
this a bit differently and usually there are a few possible modes you
can select, I'm providing a few common modes for biasing and driving
pins.

Since we have no previous hacked-up arch-specific drivers for this
we can avoid any __override_functions and we just allow this to be
properly implemented using gpiolib. Further the function is made
non-mandatory, if it is not defined for the chip it will be silently
ignored.

Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
---
 drivers/gpio/gpiolib.c     |   43 ++++++++++++++++++++++++++++++++++++++
 include/asm-generic/gpio.h |   12 ++++++++++
 include/linux/gpio.h       |   49 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 104 insertions(+), 0 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 36a2974..f79f4a3 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1573,6 +1573,49 @@ void __gpio_set_value(unsigned gpio, int value)
 EXPORT_SYMBOL_GPL(__gpio_set_value);
 
 /**
+ * gpio_set_bias() - set a gpio's bias
+ * @gpio: gpio whose bias will be set
+ * @bias: bias mode to set
+ * Context: process
+ *
+ * This is used to directly or indirectly to implement gpio_set_bias().
+ * It invokes the associated gpio_chip.set_bias() method. Usually this
+ * applies to input pins.
+ */
+void gpio_set_bias(unsigned gpio, enum gpio_bias bias)
+{
+	struct gpio_chip	*chip;
+
+	chip = gpio_to_chip(gpio);
+	/* Implementing this is not mandatory */
+	if (chip->set_bias)
+		chip->set_bias(chip, gpio - chip->base, bias);
+}
+EXPORT_SYMBOL_GPL(gpio_set_bias);
+
+/**
+ * gpio_set_drive() - set a gpio's drive mode
+ * @gpio: gpio whose drive mode will be set
+ * @drive: drive mode to set
+ * Context: process
+ *
+ * This is used to directly or indirectly to implement gpio_set_drive().
+ * It invokes the associated gpio_chip.set_drive() method. Call this
+ * before the __gpio_set_output() function to enable special drive modes.
+ */
+void gpio_set_drive(unsigned gpio, enum gpio_drive drive)
+{
+	struct gpio_chip	*chip;
+
+	chip = gpio_to_chip(gpio);
+	/* Implementing this is not mandatory */
+	if (chip->set_drive)
+		chip->set_drive(chip, gpio - chip->base, drive);
+}
+EXPORT_SYMBOL_GPL(gpio_set_drive);
+
+
+/**
  * __gpio_cansleep() - report whether gpio value access will sleep
  * @gpio: gpio in question
  * Context: any
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index ff5c660..b4971b1 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -59,6 +59,8 @@ struct device_node;
  *	returns either the value actually sensed, or zero
  * @direction_output: configures signal "offset" as output, or returns error
  * @set: assigns output value for signal "offset"
+ * @set_bias: set a certain bias for the GPIO
+ * @set_drive: set a certain drive mode for the GPIO
  * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;
  *	implementation may not sleep
  * @dbg_show: optional routine to show contents in debugfs; default code
@@ -109,6 +111,14 @@ struct gpio_chip {
 	void			(*set)(struct gpio_chip *chip,
 						unsigned offset, int value);
 
+	void			(*set_bias)(struct gpio_chip *chip,
+						unsigned offset,
+						enum gpio_bias bias);
+
+	void			(*set_drive)(struct gpio_chip *chip,
+						unsigned offset,
+						enum gpio_drive drive);
+
 	int			(*to_irq)(struct gpio_chip *chip,
 						unsigned offset);
 
@@ -158,6 +168,8 @@ extern int gpio_set_debounce(unsigned gpio, unsigned debounce);
 extern int gpio_get_value_cansleep(unsigned gpio);
 extern void gpio_set_value_cansleep(unsigned gpio, int value);
 
+extern void gpio_set_bias(unsigned gpio, enum gpio_bias bias);
+extern void gpio_set_drive(unsigned gpio, enum gpio_drive drive);
 
 /* A platform's <asm/gpio.h> code may want to inline the I/O calls when
  * the GPIO is constant and refers to some always-present controller,
diff --git a/include/linux/gpio.h b/include/linux/gpio.h
index 32720ba..6b48c15 100644
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -3,6 +3,43 @@
 
 /* see Documentation/gpio.txt */
 
+/**
+ * enum gpio_bias - bias modes for GPIOs
+ * @GPIO_BIAS_FLOAT: no specific bias, the GPIO will float or state is no
+ * 	controlled by software
+ * @GPIO_BIAS_PULL_UP: the GPIO will be pulled up (usually with high impedance
+ * 	to VDD)
+ * @GPIO_BIAS_PULL_DOWN: the GPIO will be pulled down (usually with high
+ * 	impedance to GROUND)
+ * @GPIO_BIAS_HIGH: the GPIO will be wired high, connected to VDD
+ * @GPIO_BIAS_GROUND: the GPIO will be grounded, connected to GROUND
+ */
+enum gpio_bias {
+	GPIO_BIAS_FLOAT,
+	GPIO_BIAS_PULL_UP,
+	GPIO_BIAS_PULL_DOWN,
+	GPIO_BIAS_HIGH,
+	GPIO_BIAS_GROUND,
+};
+
+/**
+ * enum gpio_drive - drive modes for GPIOs (output)
+ * @GPIO_DRIVE_PUSH_PULL: the GPIO will be driven actively high and low, this
+ *	is the most typical case and is typically achieved with two active
+ *	transistors on the output
+ * @GPIO_DRIVE_OPEN_DRAIN: the GPIO will be driven with open drain (open
+ *	collector) which means it is usually wired with other output ports
+ *	which are then pulled up with an external resistor
+ * @GPIO_DRIVE_OPEN_SOURCE: the GPIO will be driven with open drain
+ *	(open emitter) which is the same as open drain mutatis mutandis but
+ *	pulled to ground
+ */
+enum gpio_drive {
+	GPIO_DRIVE_PUSH_PULL,
+	GPIO_DRIVE_OPEN_DRAIN,
+	GPIO_DRIVE_OPEN_SOURCE,
+};
+
 #ifdef CONFIG_GENERIC_GPIO
 #include <asm/gpio.h>
 
@@ -90,6 +127,18 @@ static inline void gpio_set_value(unsigned gpio, int value)
 	WARN_ON(1);
 }
 
+static inline void gpio_set_bias(unsigned gpio, enum gpio_bias bias)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
+
+static inline void gpio_set_drive(unsigned gpio, enum gpio_drive drive)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(1);
+}
+
 static inline int gpio_cansleep(unsigned gpio)
 {
 	/* GPIO can never have been requested or set as {in,out}put */
-- 
1.7.3.2