gpio: add GPIO hogging mechanism

Based on Boris Brezillion's work this is a reworked patch
of his initial GPIO hogging mechanism.
This patch provides a way to initially configure specific GPIO
when the GPIO controller is probed.

The actual DT scanning to collect the GPIO specific data is performed
as part of gpiochip_add().

The purpose of this is to allow specific GPIOs to be configured
without any driver specific code.
This is particularly useful because board design are getting
increasingly complex and given SoC pins can now have more
than 10 mux values, a lot of connections are now dependent on
external IO muxes to switch various modes.

Specific drivers should not necessarily need to be aware of
what accounts to a specific board implementation. This board level
"description" should be best kept as part of the dts file.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 111 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index 8cad8e4..468d76a 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c
@@ -22,6 +22,7 @@
 #include <linux/of_gpio.h>
 #include <linux/pinctrl/pinctrl.h>
 #include <linux/slab.h>
+#include <linux/gpio/machine.h>
 
 #include "gpiolib.h"
 
@@ -117,6 +118,114 @@ int of_get_named_gpio_flags(struct device_node *np, const char *list_name,
 EXPORT_SYMBOL(of_get_named_gpio_flags);
 
 /**
+ * of_get_gpio_hog() - Get a GPIO hog descriptor, names and flags for GPIO API
+ * @np:		device node to get GPIO from
+ * @name:	GPIO line name
+ * @lflags:	gpio_lookup_flags - returned from of_find_gpio() or
+ *		of_get_gpio_hog()
+ * @dflags:	gpiod_flags - optional GPIO initialization flags
+ *
+ * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
+ * value on the error condition.
+ */
+static struct gpio_desc *of_get_gpio_hog(struct device_node *np,
+				  const char **name,
+				  enum gpio_lookup_flags *lflags,
+				  enum gpiod_flags *dflags)
+{
+	struct device_node *chip_np;
+	enum of_gpio_flags xlate_flags;
+	struct gpio_desc *desc;
+	struct gg_data gg_data = {
+		.flags = &xlate_flags,
+	};
+	u32 tmp;
+	int i, ret;
+
+	chip_np = np->parent;
+	if (!chip_np)
+		return ERR_PTR(-EINVAL);
+
+	xlate_flags = 0;
+	*lflags = 0;
+	*dflags = 0;
+
+	ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
+	if (ret)
+		return ERR_PTR(ret);
+
+	if (tmp > MAX_PHANDLE_ARGS)
+		return ERR_PTR(-EINVAL);
+
+	gg_data.gpiospec.args_count = tmp;
+	gg_data.gpiospec.np = chip_np;
+	for (i = 0; i < tmp; i++) {
+		ret = of_property_read_u32_index(np, "gpios", i,
+					   &gg_data.gpiospec.args[i]);
+		if (ret)
+			return ERR_PTR(ret);
+	}
+
+	gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
+	if (!gg_data.out_gpio) {
+		if (np->parent == np)
+			return ERR_PTR(-ENXIO);
+		else
+			return ERR_PTR(-EINVAL);
+	}
+
+	if (xlate_flags & OF_GPIO_ACTIVE_LOW)
+		*lflags |= GPIO_ACTIVE_LOW;
+
+	if (of_property_read_bool(np, "input"))
+		*dflags |= GPIOD_IN;
+	else if (of_property_read_bool(np, "output-low"))
+		*dflags |= GPIOD_OUT_LOW;
+	else if (of_property_read_bool(np, "output-high"))
+		*dflags |= GPIOD_OUT_HIGH;
+	else {
+		pr_warn("GPIO line %d (%s): no hogging state specified, bailing out\n",
+			desc_to_gpio(gg_data.out_gpio), np->name);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (name && of_property_read_string(np, "line-name", name))
+		*name = np->name;
+
+	desc = gg_data.out_gpio;
+
+	return desc;
+}
+
+/**
+ * of_gpiochip_scan_hogs - Scan gpio-controller and apply GPIO hog as requested
+ * @chip:	gpio chip to act on
+ *
+ * This is only used by of_gpiochip_add to request/set GPIO initial
+ * configuration.
+ */
+static void of_gpiochip_scan_hogs(struct gpio_chip *chip)
+{
+	struct gpio_desc *desc = NULL;
+	struct device_node *np;
+	const char *name;
+	enum gpio_lookup_flags lflags;
+	enum gpiod_flags dflags;
+
+	for_each_child_of_node(chip->of_node, np) {
+		if (!of_property_read_bool(np, "gpio-hog"))
+			continue;
+
+		desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
+		if (IS_ERR(desc))
+			continue;
+
+		if (gpiod_hog(desc, name, lflags, dflags))
+			continue;
+	}
+}
+
+/**
  * of_gpio_simple_xlate - translate gpio_spec to the GPIO number and flags
  * @gc:		pointer to the gpio_chip structure
  * @np:		device node of the GPIO chip
@@ -325,6 +434,8 @@ void of_gpiochip_add(struct gpio_chip *chip)
 
 	of_gpiochip_add_pin_range(chip);
 	of_node_get(chip->of_node);
+
+	of_gpiochip_scan_hogs(chip);
 }
 
 void of_gpiochip_remove(struct gpio_chip *chip)