pinctrl/gpio: Take MUX usage into account

The user space like gpioinfo only see the GPIO usage but not the
MUX usage (e.g. I2C or SPI usage) of a pin. As a user we want
to know which pin is free/safe to use. So take the MUX usage of
strict pinmux controllers into account to get a more realistic
view for ioctl GPIO_GET_LINEINFO_IOCTL.

Signed-off-by: Stefan Wahren <[e-mail]>
Tested-by: Ramon Fried <[e-mail]>
Signed-off-by: Ramon Fried <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Stefan Wahren <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpiolib.c

···
 		    test_bit(FLAG_IS_HOGGED, &desc->flags) ||
 		    test_bit(FLAG_USED_AS_IRQ, &desc->flags) ||
 		    test_bit(FLAG_EXPORT, &desc->flags) ||
-		    test_bit(FLAG_SYSFS, &desc->flags))
+		    test_bit(FLAG_SYSFS, &desc->flags) ||
+		    !pinctrl_gpio_can_use_line(chip->base + lineinfo.line_offset))
 			lineinfo.flags |= GPIOLINE_FLAG_KERNEL;
 		if (test_bit(FLAG_IS_OUT, &desc->flags))
 			lineinfo.flags |= GPIOLINE_FLAG_IS_OUT;

drivers/pinctrl/core.c

···
 	return -EINVAL;
 }
 
+bool pinctrl_gpio_can_use_line(unsigned gpio)
+{
+	struct pinctrl_dev *pctldev;
+	struct pinctrl_gpio_range *range;
+	bool result;
+	int pin;
+
+	/*
+	 * Try to obtain GPIO range, if it fails
+	 * we're probably dealing with GPIO driver
+	 * without a backing pin controller - bail out.
+	 */
+	if (pinctrl_get_device_gpio_range(gpio, &pctldev, &range))
+		return true;
+
+	mutex_lock(&pctldev->mutex);
+
+	/* Convert to the pin controllers number space */
+	pin = gpio_to_pin(range, gpio);
+
+	result = pinmux_can_be_used_for_gpio(pctldev, pin);
+
+	mutex_unlock(&pctldev->mutex);
+
+	return result;
+}
+EXPORT_SYMBOL_GPL(pinctrl_gpio_can_use_line);
+
 /**
  * pinctrl_gpio_request() - request a single pin to be used as GPIO
  * @gpio: the GPIO pin number from the GPIO subsystem number space

drivers/pinctrl/pinmux.c

···
 }
 
 /**
+ * pinmux_can_be_used_for_gpio() - check if a specific pin
+ *	is either muxed to a different function or used as gpio.
+ *
+ * @pin: the pin number in the global pin space
+ *
+ * Controllers not defined as strict will always return true,
+ * menaning that the gpio can be used.
+ */
+bool pinmux_can_be_used_for_gpio(struct pinctrl_dev *pctldev, unsigned pin)
+{
+	struct pin_desc *desc = pin_desc_get(pctldev, pin);
+	const struct pinmux_ops *ops = pctldev->desc->pmxops;
+
+	/* Can't inspect pin, assume it can be used */
+	if (!desc)
+		return true;
+
+	if (ops->strict && desc->mux_usecount)
+		return false;
+
+	return !(ops->strict && !!desc->gpio_owner);
+}
+
+/**
  * pin_request() - request a single pin to be muxed in, typically for GPIO
  * @pin: the pin number in the global pin space
  * @owner: a representation of the owner of this pin; typically the device

drivers/pinctrl/pinmux.h

···
 
 int pinmux_validate_map(const struct pinctrl_map *map, int i);
 
+bool pinmux_can_be_used_for_gpio(struct pinctrl_dev *pctldev, unsigned pin);
+
 int pinmux_request_gpio(struct pinctrl_dev *pctldev,
 			struct pinctrl_gpio_range *range,
 			unsigned pin, unsigned gpio);
···
 static inline int pinmux_validate_map(const struct pinctrl_map *map, int i)
 {
 	return 0;
+}
+
+static inline bool pinmux_can_be_used_for_gpio(struct pinctrl_dev *pctldev,
+					       unsigned pin)
+{
+	return true;
 }
 
 static inline int pinmux_request_gpio(struct pinctrl_dev *pctldev,

include/linux/pinctrl/consumer.h

···
 #ifdef CONFIG_PINCTRL
 
 /* External interface to pin control */
+extern bool pinctrl_gpio_can_use_line(unsigned gpio);
 extern int pinctrl_gpio_request(unsigned gpio);
 extern void pinctrl_gpio_free(unsigned gpio);
 extern int pinctrl_gpio_direction_input(unsigned gpio);
···
 #endif
 
 #else /* !CONFIG_PINCTRL */
+
+static inline bool pinctrl_gpio_can_use_line(unsigned gpio)
+{
+	return true;
+}
 
 static inline int pinctrl_gpio_request(unsigned gpio)
 {