[PATCH RFC] gpiolib: Take MUX usage into account

[Stefan Wahren <stefan.wahren@xxxxxxxx>]

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 into account to get a more
realistic view for ioctl GPIO_GET_LINEINFO_IOCTL.

Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
---
 drivers/gpio/gpiolib.c           |  3 ++-
 drivers/pinctrl/core.c           | 23 +++++++++++++++++++++++
 drivers/pinctrl/pinmux.c         | 17 +++++++++++++++++
 drivers/pinctrl/pinmux.h         |  7 +++++++
 include/linux/pinctrl/consumer.h |  6 ++++++
 5 files changed, 55 insertions(+), 1 deletion(-)

Hi,

as proposed in a recent discussion [1], this is a hack to improve gpioinfo.
I think this could a start point for a discussion.

Obvious drawback is the resulting overhead for the ioctl call.

Stefan

[1] - https://marc.info/?l=linux-gpio&m=154644476313636

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 1651d7f..da3b008 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1075,7 +1075,8 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		    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_is_in_use(chip->base + lineinfo.line_offset))
 			lineinfo.flags |= GPIOLINE_FLAG_KERNEL;
 		if (test_bit(FLAG_IS_OUT, &desc->flags))
 			lineinfo.flags |= GPIOLINE_FLAG_IS_OUT;
diff --git a/drivers/pinctrl/core.c b/drivers/pinctrl/core.c
index c6ff4d5..6e097e4 100644
--- a/drivers/pinctrl/core.c
+++ b/drivers/pinctrl/core.c
@@ -760,6 +760,29 @@ int pinctrl_get_group_selector(struct pinctrl_dev *pctldev,
 	return -EINVAL;
 }
 
+bool pinctrl_gpio_is_in_use(unsigned gpio)
+{
+	struct pinctrl_dev *pctldev;
+	struct pinctrl_gpio_range *range;
+	bool result;
+	int pin;
+
+	if (pinctrl_get_device_gpio_range(gpio, &pctldev, &range))
+		return false;
+
+	mutex_lock(&pctldev->mutex);
+
+	/* Convert to the pin controllers number space */
+	pin = gpio_to_pin(range, gpio);
+
+	result = pinmux_is_in_use(pctldev, pin);
+
+	mutex_unlock(&pctldev->mutex);
+
+	return result;
+}
+EXPORT_SYMBOL_GPL(pinctrl_gpio_is_in_use);
+
 /**
  * pinctrl_gpio_request() - request a single pin to be used as GPIO
  * @gpio: the GPIO pin number from the GPIO subsystem number space
diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
index 4d0cc18..0a5bab2 100644
--- a/drivers/pinctrl/pinmux.c
+++ b/drivers/pinctrl/pinmux.c
@@ -71,6 +71,23 @@ int pinmux_validate_map(const struct pinctrl_map *map, int i)
 	return 0;
 }
 
+bool pinmux_is_in_use(struct pinctrl_dev *pctldev, unsigned pin)
+{
+	struct pin_desc *desc = pin_desc_get(pctldev, pin);
+
+	if (!desc) {
+		dev_err(pctldev->dev,
+			"pin %u is not registered so it cannot be requested\n",
+			pin);
+		return false;
+	}
+
+	if (desc->mux_usecount)
+		return true;
+
+	return !!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
diff --git a/drivers/pinctrl/pinmux.h b/drivers/pinctrl/pinmux.h
index 3319535..1da2a75 100644
--- a/drivers/pinctrl/pinmux.h
+++ b/drivers/pinctrl/pinmux.h
@@ -16,6 +16,8 @@ int pinmux_check_ops(struct pinctrl_dev *pctldev);
 
 int pinmux_validate_map(const struct pinctrl_map *map, int i);
 
+bool pinmux_is_in_use(struct pinctrl_dev *pctldev, unsigned pin);
+
 int pinmux_request_gpio(struct pinctrl_dev *pctldev,
 			struct pinctrl_gpio_range *range,
 			unsigned pin, unsigned gpio);
@@ -43,6 +45,11 @@ static inline int pinmux_validate_map(const struct pinctrl_map *map, int i)
 	return 0;
 }
 
+static inline bool pinmux_is_in_use(struct pinctrl_dev *pctldev, unsigned pin)
+{
+	return false;
+}
+
 static inline int pinmux_request_gpio(struct pinctrl_dev *pctldev,
 			struct pinctrl_gpio_range *range,
 			unsigned pin, unsigned gpio)
diff --git a/include/linux/pinctrl/consumer.h b/include/linux/pinctrl/consumer.h
index 0412cc9..0093a2b 100644
--- a/include/linux/pinctrl/consumer.h
+++ b/include/linux/pinctrl/consumer.h
@@ -25,6 +25,7 @@ struct device;
 #ifdef CONFIG_PINCTRL
 
 /* External interface to pin control */
+extern bool pinctrl_gpio_is_in_use(unsigned gpio);
 extern int pinctrl_gpio_request(unsigned gpio);
 extern void pinctrl_gpio_free(unsigned gpio);
 extern int pinctrl_gpio_direction_input(unsigned gpio);
@@ -62,6 +63,11 @@ static inline int pinctrl_pm_select_idle_state(struct device *dev)
 
 #else /* !CONFIG_PINCTRL */
 
+static inline bool pinctrl_gpio_is_in_use(unsigned gpio)
+{
+	return 0;
+}
+
 static inline int pinctrl_gpio_request(unsigned gpio)
 {
 	return 0;
-- 
2.7.4