pinctrl: allow to mark pin functions as requestable GPIOs

The name of the pin function has no real meaning to pinctrl core and is
there only for human readability of device properties. Some pins are
muxed as GPIOs but for "strict" pinmuxers it's impossible to request
them as GPIOs if they're bound to a devide - even if their function name
explicitly says "gpio". Add a new field to struct pinfunction that
allows to pass additional flags to pinctrl core. While we could go with
a boolean "is_gpio" field, a flags field is more future-proof.

If the PINFUNCTION_FLAG_GPIO is set for a given function, the pin muxed
to it can be requested as GPIO even on strict pin controllers. Add a new
callback to struct pinmux_ops - function_is_gpio() - that allows pinmux
core to inspect a function and see if it's a GPIO one. Provide a generic
implementation of this callback.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinmux.c

@@ -89,13 +89,20 @@ bool pinmux_can_be_used_for_gpio(struct pinctrl_dev *pctldev, unsigned int pin)
 {
 	struct pin_desc *desc = pin_desc_get(pctldev, pin);
 	const struct pinmux_ops *ops = pctldev->desc->pmxops;
+	const struct pinctrl_setting_mux *mux_setting;
+	bool func_is_gpio = false;
 
 	/* Can't inspect pin, assume it can be used */
 	if (!desc || !ops)
 		return true;
 
+	mux_setting = desc->mux_setting;
+
 	guard(mutex)(&desc->mux_lock);
-	if (ops->strict && desc->mux_usecount)
+	if (mux_setting && ops->function_is_gpio)
+		func_is_gpio = ops->function_is_gpio(pctldev, mux_setting->func);
+
+	if (ops->strict && desc->mux_usecount && !func_is_gpio)
 		return false;
 
 	return !(ops->strict && !!desc->gpio_owner);
@@ -116,7 +123,9 @@ static int pin_request(struct pinctrl_dev *pctldev,
 {
 	struct pin_desc *desc;
 	const struct pinmux_ops *ops = pctldev->desc->pmxops;
+	const struct pinctrl_setting_mux *mux_setting;
 	int status = -EINVAL;
+	bool gpio_ok = false;
 
 	desc = pin_desc_get(pctldev, pin);
 	if (desc == NULL) {
@@ -126,11 +135,21 @@ static int pin_request(struct pinctrl_dev *pctldev,
 		goto out;
 	}
 
+	mux_setting = desc->mux_setting;
+
 	dev_dbg(pctldev->dev, "request pin %d (%s) for %s\n",
 		pin, desc->name, owner);
 
 	scoped_guard(mutex, &desc->mux_lock) {
-		if ((!gpio_range || ops->strict) &&
+		if (mux_setting) {
+			if (ops->function_is_gpio)
+				gpio_ok = ops->function_is_gpio(pctldev,
+								mux_setting->func);
+		} else {
+			gpio_ok = true;
+		}
+
+		if ((!gpio_range || ops->strict) && !gpio_ok &&
 		    desc->mux_usecount && strcmp(desc->mux_owner, owner)) {
 			dev_err(pctldev->dev,
 				"pin %s already requested by %s; cannot claim for %s\n",
@@ -138,7 +157,7 @@ static int pin_request(struct pinctrl_dev *pctldev,
 			goto out;
 		}
 
-		if ((gpio_range || ops->strict) && desc->gpio_owner) {
+		if ((gpio_range || ops->strict) && !gpio_ok && desc->gpio_owner) {
 			dev_err(pctldev->dev,
 				"pin %s already requested by %s; cannot claim for %s\n",
 				desc->name, desc->gpio_owner, owner);
@@ -861,6 +880,27 @@ pinmux_generic_get_function(struct pinctrl_dev *pctldev, unsigned int selector)
 }
 EXPORT_SYMBOL_GPL(pinmux_generic_get_function);
 
+/**
+ * pinmux_generic_function_is_gpio() - returns true if given function is a GPIO
+ * @pctldev: pin controller device
+ * @selector: function number
+ *
+ * Returns:
+ * True if given function is a GPIO, false otherwise.
+ */
+bool pinmux_generic_function_is_gpio(struct pinctrl_dev *pctldev,
+				     unsigned int selector)
+{
+	struct function_desc *function;
+
+	function = radix_tree_lookup(&pctldev->pin_function_tree, selector);
+	if (!function)
+		return false;
+
+	return function->func->flags & PINFUNCTION_FLAG_GPIO;
+}
+EXPORT_SYMBOL_GPL(pinmux_generic_function_is_gpio);
+
 /**
  * pinmux_generic_add_function() - adds a function group
  * @pctldev: pin controller device

drivers/pinctrl/pinmux.h

@@ -169,6 +169,9 @@ int pinmux_generic_remove_function(struct pinctrl_dev *pctldev,
 
 void pinmux_generic_free_functions(struct pinctrl_dev *pctldev);
 
+bool pinmux_generic_function_is_gpio(struct pinctrl_dev *pctldev,
+				     unsigned int selector);
+
 #else
 
 static inline void pinmux_generic_free_functions(struct pinctrl_dev *pctldev)

include/linux/pinctrl/pinctrl.h

@@ -11,6 +11,7 @@
 #ifndef __LINUX_PINCTRL_PINCTRL_H
 #define __LINUX_PINCTRL_PINCTRL_H
 
+#include <linux/bits.h>
 #include <linux/types.h>
 
 struct device;
@@ -206,16 +207,20 @@ extern int pinctrl_get_group_pins(struct pinctrl_dev *pctldev,
 				  const char *pin_group, const unsigned int **pins,
 				  unsigned int *num_pins);
 
+#define PINFUNCTION_FLAG_GPIO	BIT(0)
+
 /**
  * struct pinfunction - Description about a function
  * @name: Name of the function
  * @groups: An array of groups for this function
  * @ngroups: Number of groups in @groups
+ * @flags: Additional pin function flags
  */
 struct pinfunction {
 	const char *name;
 	const char * const *groups;
 	size_t ngroups;
+	unsigned long flags;
 };
 
 /* Convenience macro to define a single named pinfunction */
@@ -226,6 +231,15 @@ struct pinfunction {
 		.ngroups = (_ngroups),			\
 	}
 
+/* Same as PINCTRL_PINFUNCTION() but for the GPIO category of functions */
+#define PINCTRL_GPIO_PINFUNCTION(_name, _groups, _ngroups)	\
+(struct pinfunction) {						\
+		.name = (_name),				\
+		.groups = (_groups),				\
+		.ngroups = (_ngroups),				\
+		.flags = PINFUNCTION_FLAG_GPIO,			\
+	}
+
 #if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_PINCTRL)
 extern struct pinctrl_dev *of_pinctrl_get(struct device_node *np);
 #else

include/linux/pinctrl/pinmux.h

@@ -66,6 +66,8 @@ struct pinmux_ops {
 				    unsigned int selector,
 				    const char * const **groups,
 				    unsigned int *num_groups);
+	bool (*function_is_gpio) (struct pinctrl_dev *pctldev,
+				  unsigned int selector);
 	int (*set_mux) (struct pinctrl_dev *pctldev, unsigned int func_selector,
 			unsigned int group_selector);
 	int (*gpio_request_enable) (struct pinctrl_dev *pctldev,