gpiolib: add support for bias pull disable

This change prepares the gpio core to look at firmware flags and set
'FLAG_BIAS_DISABLE' if necessary. It works in similar way to
'GPIO_PULL_DOWN' and 'GPIO_PULL_UP'.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>

drivers/gpio/gpiolib.c

@@ -3945,16 +3945,20 @@ int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
 	if (lflags & GPIO_OPEN_SOURCE)
 		set_bit(FLAG_OPEN_SOURCE, &desc->flags);
 
-	if ((lflags & GPIO_PULL_UP) && (lflags & GPIO_PULL_DOWN)) {
+	if (((lflags & GPIO_PULL_UP) && (lflags & GPIO_PULL_DOWN)) ||
+	    ((lflags & GPIO_PULL_UP) && (lflags & GPIO_PULL_DISABLE)) ||
+	    ((lflags & GPIO_PULL_DOWN) && (lflags & GPIO_PULL_DISABLE))) {
 		gpiod_err(desc,
-			  "both pull-up and pull-down enabled, invalid configuration\n");
+			  "multiple pull-up, pull-down or pull-disable enabled, invalid configuration\n");
 		return -EINVAL;
 	}
 
 	if (lflags & GPIO_PULL_UP)
 		set_bit(FLAG_PULL_UP, &desc->flags);
 	else if (lflags & GPIO_PULL_DOWN)
 		set_bit(FLAG_PULL_DOWN, &desc->flags);
+	else if (lflags & GPIO_PULL_DISABLE)
+		set_bit(FLAG_BIAS_DISABLE, &desc->flags);
 
 	ret = gpiod_set_transitory(desc, (lflags & GPIO_TRANSITORY));
 	if (ret < 0)

include/linux/gpio/machine.h

@@ -14,6 +14,7 @@ enum gpio_lookup_flags {
 	GPIO_TRANSITORY			= (1 << 3),
 	GPIO_PULL_UP			= (1 << 4),
 	GPIO_PULL_DOWN			= (1 << 5),
+	GPIO_PULL_DISABLE		= (1 << 6),
 
 	GPIO_LOOKUP_FLAGS_DEFAULT	= GPIO_ACTIVE_HIGH | GPIO_PERSISTENT,
 };