drivers: gpio: mcp23xxx: fix drive mode validation for input pins

The drive mode validation added in commit ede19a4 was rejecting
valid configurations for input pins. The validation ensures that
GPIO_SINGLE_ENDED and GPIO_LINE_OPEN_DRAIN flags match the hardware
capabilities of each MCP23xxx variant (push-pull vs open-drain).

However, this validation was applied to all pin configurations,
including input pins. Input pins do not have a drive mode, so
applications typically configure them without setting drive mode flags.
This caused the validation to incorrectly reject input pin configurations
with -ENOTSUP.

Fix by only validating drive mode flags when GPIO_OUTPUT is set.
Input pins now configure successfully, while output pins still receive
proper validation to ensure the requested drive mode matches the
hardware capabilities.

Fixes: ede19a4 ("drivers: mcp23xxx: add support for open-drain ...")
Signed-off-by: Cliff Brake <[email protected]>

Author: cbrake

drivers/gpio/gpio_mcp23xxx.c

@@ -180,10 +180,18 @@ static int mcp23xxx_pin_cfg(const struct device *dev, gpio_pin_t pin, gpio_flags
 
 	k_sem_take(&drv_data->lock, K_FOREVER);
 
-	if ((bool)(flags & GPIO_SINGLE_ENDED) != config->is_open_drain ||
-	    (bool)(flags & GPIO_LINE_OPEN_DRAIN) != config->is_open_drain) {
-		ret = -ENOTSUP;
-		goto done;
+	/* Validate drive mode flags for output pins only.
+	 * The MCP23xxx hardware has a fixed drive mode per chip variant:
+	 * - MCP23x08/x17: Push-pull outputs only
+	 * - MCP23x09/x18: Open-drain outputs only
+	 * Input pins don't have a drive mode, so skip validation for them.
+	 */
+	if (flags & GPIO_OUTPUT) {
+		if ((bool)(flags & GPIO_SINGLE_ENDED) != config->is_open_drain ||
+		    (bool)(flags & GPIO_LINE_OPEN_DRAIN) != config->is_open_drain) {
+			ret = -ENOTSUP;
+			goto done;
+		}
 	}
 
 	ret = setup_pin_dir(dev, pin, flags);