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

From: Rohit Vaswani
Date: Mon Apr 25 2011 - 14:53:01 EST

On 4/17/2011 2:37 PM, Linus Walleij wrote:
From: Linus Walleij<linus.walleij@xxxxxxxxxx>

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.
This is a great start for something that the msm tree has been doing internally through its gpiomux architecture.
Currently, msm has to configure a the pinmux in addition to the drive and the bias, so we would like to make this more powerful to support
different gpio parameters. This has been mentioned previously - but a way to define a custom config and set and get its parameters seems like
a more extensible model.

Signed-off-by: Linus Walleij<linus.walleij@xxxxxxxxxx>
---
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);
With the pinmux architecture a gpio can be multiplexed with different functional modules.
Another API to select this would make it more powerful. At boot a lot of gpios are configured by the board-file.
How do you feel about another API that can accepts the gpio config parameters (void *data) and set them all at once?
This would make it more generic to suit different gpio parameters that an arch might have.


/* 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 */


Thanks,
Rohit Vaswani

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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