[PATCH V2 2/3] gpio: gpiolib: Support for open drain/collector gpios

Laxman Dewangan
2012-02-17T14:58:53Z

Adding support for the open drain gpio on which client
can specify the open drain property through GPIO flag
GPIOF_OPEN_DRAIN at the time of gpio request.
The open drain pins are normally pulled high and it
cannot be driven to output with value of 1 and so
when client request for setting the pin to HIGH, the
gpio will be set to input direction to make pin in tristate
and hence PULL-UP on pins will make the state to HIGH.
The open drain pin can be driven to LOW by setting output
with value of 0.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
---
drivers/gpio/gpiolib.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
include/linux/gpio.h | 3 +++
2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 17fdf4b..9940777 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -58,6 +58,7 @@ struct gpio_desc {
#define FLAG_TRIG_FALL 5 /* trigger on falling edge */
#define FLAG_TRIG_RISE 6 /* trigger on rising edge */
#define FLAG_ACTIVE_LOW 7 /* sysfs value has active low */
+#define FLAG_OPEN_DRAIN 8 /* Gpio is open drain type */

#define ID_SHIFT 16 /* add new flags before this one */

@@ -1261,6 +1262,7 @@ void gpio_free(unsigned gpio)
module_put(desc->chip->owner);
clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
clear_bit(FLAG_REQUESTED, &desc->flags);
+ clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
} else
WARN_ON(extra_checks);

@@ -1282,6 +1284,9 @@ int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)
if (err)
return err;

+ if (flags & GPIOF_OPEN_DRAIN)
+ set_bit(FLAG_OPEN_DRAIN, &gpio_desc[gpio].flags);
+
if (flags & GPIOF_DIR_IN)
err = gpio_direction_input(gpio);
else
@@ -1431,6 +1436,10 @@ int gpio_direction_output(unsigned gpio, int value)
struct gpio_desc *desc = &gpio_desc[gpio];
int status = -EINVAL;

+ /* Open drain pin should not be driven to 1 */
+ if (value && test_bit(FLAG_OPEN_DRAIN, &desc->flags))
+ return gpio_direction_input(gpio);
+
spin_lock_irqsave(&gpio_lock, flags);

if (!gpio_is_valid(gpio))
@@ -1567,6 +1576,31 @@ int __gpio_get_value(unsigned gpio)
}
EXPORT_SYMBOL_GPL(__gpio_get_value);

+/*
+ * _gpio_set_open_drain_value() - Set the open drain gpio's value.
+ * @gpio: Gpio whose state need to be set.
+ * @chip: Gpio chip.
+ * @value: Non-zero for setting it HIGH otherise it will set to LOW.
+ */
+static void _gpio_set_open_drain_value(unsigned gpio,
+ struct gpio_chip *chip, int value)
+{
+ int err = 0;
+ if (value) {
+ err = chip->direction_input(chip, gpio - chip->base);
+ if (!err)
+ clear_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
+ } else {
+ err = chip->direction_output(chip, gpio - chip->base, 0);
+ if (!err)
+ set_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
+ }
+ trace_gpio_direction(gpio, value, err);
+ if (err < 0)
+ pr_err("%s: Error in set_value for open drain gpio%d err %d\n",
+ __func__, gpio, err);
+}
+
/**
* __gpio_set_value() - assign a gpio's value
* @gpio: gpio whose value will be assigned
@@ -1583,7 +1617,10 @@ void __gpio_set_value(unsigned gpio, int value)
chip = gpio_to_chip(gpio);
WARN_ON(chip->can_sleep);
trace_gpio_value(gpio, 0, value);
- chip->set(chip, gpio - chip->base, value);
+ if (test_bit(FLAG_OPEN_DRAIN, &gpio_desc[gpio].flags))
+ _gpio_set_open_drain_value(gpio, chip, value);
+ else
+ chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(__gpio_set_value);

@@ -1650,7 +1687,10 @@ void gpio_set_value_cansleep(unsigned gpio, int value)
might_sleep_if(extra_checks);
chip = gpio_to_chip(gpio);
trace_gpio_value(gpio, 0, value);
- chip->set(chip, gpio - chip->base, value);
+ if (test_bit(FLAG_OPEN_DRAIN, &gpio_desc[gpio].flags))
+ _gpio_set_open_drain_value(gpio, chip, value);
+ else
+ chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(gpio_set_value_cansleep);

diff --git a/include/linux/gpio.h b/include/linux/gpio.h
index 38ac48b..66a5b2e 100644
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -14,6 +14,9 @@
#define GPIOF_OUT_INIT_LOW (GPIOF_DIR_OUT | GPIOF_INIT_LOW)
#define GPIOF_OUT_INIT_HIGH (GPIOF_DIR_OUT | GPIOF_INIT_HIGH)

+/* Gpio pin is open drain */
+#define GPIOF_OPEN_DRAIN (1 << 2)
+
/**
* struct gpio - a structure describing a GPIO with configuration
* @gpio: the GPIO number
--
1.7.1.1