[PATCH 4/5] gpiolib: disable bias on inputs when pull up/down are both set

[Kent Gibson <warthog618@xxxxxxxxx>]

This patch allows pull up/down bias to be disabled, allowing
the line to float or to be biased only by external circuitry.
Use case is for where the bias has been applied previously,
either by default or by the user, but that setting may
conflict with the current use of the line.

Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
---
 drivers/gpio/gpiolib.c | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index a634c340920b..f0665ea396cd 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -539,11 +539,6 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 	    (lflags & GPIOHANDLE_REQUEST_OUTPUT))
 		return -EINVAL;
 
-	/* Same with pull-up and pull-down. */
-	if ((lflags & GPIOHANDLE_REQUEST_PULL_UP) &&
-	    (lflags & GPIOHANDLE_REQUEST_PULL_DOWN))
-		return -EINVAL;
-
 	/*
 	 * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
 	 * the hardware actually supports enabling both at the same time the
@@ -935,14 +930,6 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
 	     (lflags & GPIOHANDLE_REQUEST_PULL_DOWN)))
 		return -EINVAL;
 
-	/*
-	 * Do not allow both pull-up and pull-down flags to be set as they
-	 *  are contradictory.
-	 */
-	if ((lflags & GPIOHANDLE_REQUEST_PULL_UP) &&
-	    (lflags & GPIOHANDLE_REQUEST_PULL_DOWN))
-		return -EINVAL;
-
 	le = kzalloc(sizeof(*le), GFP_KERNEL);
 	if (!le)
 		return -ENOMEM;
@@ -2931,6 +2918,7 @@ static int gpio_set_config(struct gpio_chip *gc, unsigned offset,
 	unsigned arg;
 
 	switch (mode) {
+	case PIN_CONFIG_BIAS_DISABLE:
 	case PIN_CONFIG_BIAS_PULL_DOWN:
 	case PIN_CONFIG_BIAS_PULL_UP:
 		arg = 1;
@@ -2991,7 +2979,11 @@ int gpiod_direction_input(struct gpio_desc *desc)
 	if (ret == 0)
 		clear_bit(FLAG_IS_OUT, &desc->flags);
 
-	if (test_bit(FLAG_PULL_UP, &desc->flags))
+	if (test_bit(FLAG_PULL_UP, &desc->flags) &&
+		test_bit(FLAG_PULL_DOWN, &desc->flags))
+		gpio_set_config(chip, gpio_chip_hwgpio(desc),
+				PIN_CONFIG_BIAS_DISABLE);
+	else if (test_bit(FLAG_PULL_UP, &desc->flags))
 		gpio_set_config(chip, gpio_chip_hwgpio(desc),
 				PIN_CONFIG_BIAS_PULL_UP);
 	else if (test_bit(FLAG_PULL_DOWN, &desc->flags))
@@ -4462,7 +4454,7 @@ int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
 
 	if (lflags & GPIO_PULL_UP)
 		set_bit(FLAG_PULL_UP, &desc->flags);
-	else if (lflags & GPIO_PULL_DOWN)
+	if (lflags & GPIO_PULL_DOWN)
 		set_bit(FLAG_PULL_DOWN, &desc->flags);
 
 	ret = gpiod_set_transitory(desc, (lflags & GPIO_TRANSITORY));
-- 
2.23.0