pinctrl: apple: Implement GPIO func check callback

This function will check if the indicated function enumerator
i.e. the value set into bits 5 and 6 of the pin configuration
register, is zero and thus corresponds to the GPIO mode of the
pin.

This may be necessary to know since the pin controller is
flagged as "strict": once you set a pin *explicitly* to GPIO
mode using function 0, the core is unaware that this is
actually the GPIO mode, and clients may be denied to
retrieve the pin as a GPIO.

Currently none of the in-kernel device trees sets any pin to
GPIO mode, but this may happen any day.

Reviewed-by: Sven Peter <sven@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>

Author: linusw

drivers/pinctrl/pinctrl-apple-gpio.c

@@ -170,6 +170,13 @@ static const struct pinctrl_ops apple_gpio_pinctrl_ops = {
 
 /* Pin multiplexer functions */
 
+static bool apple_gpio_pinmux_func_is_gpio(struct pinctrl_dev *pctldev,
+					   unsigned int selector)
+{
+	/* Function selector 0 is always the GPIO mode */
+	return (selector == 0);
+}
+
 static int apple_gpio_pinmux_set(struct pinctrl_dev *pctldev, unsigned int func,
 				 unsigned int group)
 {
@@ -186,6 +193,7 @@ static const struct pinmux_ops apple_gpio_pinmux_ops = {
 	.get_functions_count = pinmux_generic_get_function_count,
 	.get_function_name = pinmux_generic_get_function_name,
 	.get_function_groups = pinmux_generic_get_function_groups,
+	.function_is_gpio = apple_gpio_pinmux_func_is_gpio,
 	.set_mux = apple_gpio_pinmux_set,
 	.strict = true,
 };