gpio: gpiolib: Support for open drain/collector gpios

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>
Reviwed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 42 insertions, 2 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e633a2afbe90..5d25a33d5359 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 */
 
@@ -1264,6 +1265,7 @@ 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);
 
@@ -1285,6 +1287,9 @@ 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
@@ -1434,6 +1439,10 @@ 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))
@@ -1570,6 +1579,31 @@ 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
@@ -1586,7 +1620,10 @@ 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);
 
@@ -1653,7 +1690,10 @@ 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);