[RFC] gpiolib: Fix gpio_direction_* for single direction GPIOs

[Ricardo Ribalda Delgado]

GPIOs with no programmable direction are not required to implement
direction_output nor direction_input.

If we try to set an output direction on an output-only GPIO or input
direction on an input-only GPIO simply return 0.

This allows this single direction GPIO to be used by libgpiod.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.riba...@gmail.com>
---
 drivers/gpio/gpiolib.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index af853749e0bb..3c09bf70e7ab 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2517,19 +2517,27 @@ EXPORT_SYMBOL_GPL(gpiochip_free_own_desc);
 int gpiod_direction_input(struct gpio_desc *desc)
 {
        struct gpio_chip        *chip;
-       int                     status = -EINVAL;
+       int                     status = 0;
 
        VALIDATE_DESC(desc);
        chip = desc->gdev->chip;
 
-       if (!chip->get || !chip->direction_input) {
+       if (!chip->get && chip->direction_input) {
                gpiod_warn(desc,
-                       "%s: missing get() or direction_input() operations\n",
+                       "%s: missing get() and direction_input() operations\n",
                        __func__);
                return -EIO;
        }
 
-       status = chip->direction_input(chip, gpio_chip_hwgpio(desc));
+       if (chip->direction_input) {
+               status = chip->direction_input(chip, gpio_chip_hwgpio(desc));
+       } else if (chip->get_direction &&
+                 (chip->get_direction(chip, gpio_chip_hwgpio(desc)) != 1)) {
+               gpiod_warn(desc,
+                       "%s: missing direction_input() operation\n",
+                       __func__);
+               return -EIO;
+       }
        if (status == 0)
                clear_bit(FLAG_IS_OUT, &desc->flags);
 
@@ -2551,16 +2559,28 @@ static int gpiod_direction_output_raw_commit(struct 
gpio_desc *desc, int value)
 {
        struct gpio_chip *gc = desc->gdev->chip;
        int val = !!value;
-       int ret;
+       int ret = 0;
 
-       if (!gc->set || !gc->direction_output) {
+       if (!gc->set && !gc->direction_output) {
                gpiod_warn(desc,
-                      "%s: missing set() or direction_output() operations\n",
+                      "%s: missing set() and direction_output() operations\n",
                       __func__);
                return -EIO;
        }
 
-       ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), val);
+       if (gc->direction_output) {
+               ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), val);
+       } else {
+               if (gc->get_direction &&
+                   gc->get_direction(gc, gpio_chip_hwgpio(desc))) {
+                       gpiod_warn(desc,
+                               "%s: missing direction_output() operation\n",
+                               __func__);
+                       return -EIO;
+               }
+               gc->set(gc, gpio_chip_hwgpio(desc), val);
+       }
+
        if (!ret)
                set_bit(FLAG_IS_OUT, &desc->flags);
        trace_gpio_value(desc_to_gpio(desc), 0, val);
-- 
2.18.0