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>

3 files changed, 219 insertions, 19 deletions

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index 8cad8e400b44..468d76ac1e84 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)
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 1ca9295b2c10..15837263dbb3 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -315,6 +315,7 @@ EXPORT_SYMBOL_GPL(gpiochip_add);
 
 /* Forward-declaration */
 static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip);
+static void gpiochip_free_hogs(struct gpio_chip *chip);
 
 /**
  * gpiochip_remove() - unregister a gpio_chip
@@ -333,6 +334,7 @@ void gpiochip_remove(struct gpio_chip *chip)
 
         acpi_gpiochip_remove(chip);
         gpiochip_remove_pin_ranges(chip);
+        gpiochip_free_hogs(chip);
         of_gpiochip_remove(chip);
 
         spin_lock_irqsave(&gpio_lock, flags);
@@ -866,6 +868,7 @@ static bool __gpiod_free(struct gpio_desc *desc)
                 clear_bit(FLAG_REQUESTED, &desc->flags);
                 clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
                 clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
+                clear_bit(FLAG_IS_HOGGED, &desc->flags);
                 ret = true;
         }
 
@@ -1840,6 +1843,47 @@ struct gpio_desc *__must_check __gpiod_get_optional(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(__gpiod_get_optional);
 
+
+/**
+ * gpiod_configure_flags - helper function to configure a given GPIO
+ * @desc:       gpio whose value will be assigned
+ * @con_id:     function within the GPIO consumer
+ * @lflags:     gpio_lookup_flags - returned from of_find_gpio() or
+ *              of_get_gpio_hog()
+ * @dflags:     gpiod_flags - optional GPIO initialization flags
+ *
+ * Return 0 on success, -ENOENT if no GPIO has been assigned to the
+ * requested function and/or index, or another IS_ERR() code if an error
+ * occurred while trying to acquire the GPIO.
+ */
+static int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
+                unsigned long lflags, enum gpiod_flags dflags)
+{
+        int status;
+
+        if (lflags & GPIO_ACTIVE_LOW)
+                set_bit(FLAG_ACTIVE_LOW, &desc->flags);
+        if (lflags & GPIO_OPEN_DRAIN)
+                set_bit(FLAG_OPEN_DRAIN, &desc->flags);
+        if (lflags & GPIO_OPEN_SOURCE)
+                set_bit(FLAG_OPEN_SOURCE, &desc->flags);
+
+        /* No particular flag request, return here... */
+        if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
+                pr_debug("no flags found for %s\n", con_id);
+                return 0;
+        }
+
+        /* Process flags */
+        if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
+                status = gpiod_direction_output(desc,
+                                              dflags & GPIOD_FLAGS_BIT_DIR_VAL);
+        else
+                status = gpiod_direction_input(desc);
+
+        return status;
+}
+
 /**
  * gpiod_get_index - obtain a GPIO from a multi-index GPIO function
  * @dev:        GPIO consumer, can be NULL for system-global GPIOs
@@ -1889,28 +1933,10 @@ struct gpio_desc *__must_check __gpiod_get_index(struct device *dev,
         }
 
         status = gpiod_request(desc, con_id);
-
         if (status < 0)
                 return ERR_PTR(status);
 
-        if (lookupflags & GPIO_ACTIVE_LOW)
-                set_bit(FLAG_ACTIVE_LOW, &desc->flags);
-        if (lookupflags & GPIO_OPEN_DRAIN)
-                set_bit(FLAG_OPEN_DRAIN, &desc->flags);
-        if (lookupflags & GPIO_OPEN_SOURCE)
-                set_bit(FLAG_OPEN_SOURCE, &desc->flags);
-
-        /* No particular flag request, return here... */
-        if (!(flags & GPIOD_FLAGS_BIT_DIR_SET))
-                return desc;
-
-        /* Process flags */
-        if (flags & GPIOD_FLAGS_BIT_DIR_OUT)
-                status = gpiod_direction_output(desc,
-                                              flags & GPIOD_FLAGS_BIT_DIR_VAL);
-        else
-                status = gpiod_direction_input(desc);
-
+        status = gpiod_configure_flags(desc, con_id, lookupflags, flags);
         if (status < 0) {
                 dev_dbg(dev, "setup of GPIO %s failed\n", con_id);
                 gpiod_put(desc);
@@ -2006,6 +2032,66 @@ struct gpio_desc *__must_check __gpiod_get_index_optional(struct device *dev,
 EXPORT_SYMBOL_GPL(__gpiod_get_index_optional);
 
 /**
+ * gpiod_hog - Hog the specified GPIO desc given the provided flags
+ * @desc:       gpio whose value will be assigned
+ * @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
+ */
+int gpiod_hog(struct gpio_desc *desc, const char *name,
+              unsigned long lflags, enum gpiod_flags dflags)
+{
+        struct gpio_chip *chip;
+        struct gpio_desc *local_desc;
+        int hwnum;
+        int status;
+
+        chip = gpiod_to_chip(desc);
+        hwnum = gpio_chip_hwgpio(desc);
+
+        local_desc = gpiochip_request_own_desc(chip, hwnum, name);
+        if (IS_ERR(local_desc)) {
+                pr_debug("requesting own GPIO %s failed\n", name);
+                return PTR_ERR(local_desc);
+        }
+
+        status = gpiod_configure_flags(desc, name, lflags, dflags);
+        if (status < 0) {
+                pr_debug("setup of GPIO %s failed\n", name);
+                gpiochip_free_own_desc(desc);
+                return status;
+        }
+
+        /* Mark GPIO as hogged so it can be identified and removed later */
+        set_bit(FLAG_IS_HOGGED, &desc->flags);
+
+        pr_info("GPIO line %d (%s) hogged as %s%s\n",
+                desc_to_gpio(desc), name,
+                (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ? "output" : "input",
+                (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ?
+                  (dflags&GPIOD_FLAGS_BIT_DIR_VAL) ? "/high" : "/low":"");
+
+        return 0;
+}
+
+/**
+ * gpiochip_free_hogs - Scan gpio-controller chip and release GPIO hog
+ * @chip:       gpio chip to act on
+ *
+ * This is only used by of_gpiochip_remove to free hogged gpios
+ */
+static void gpiochip_free_hogs(struct gpio_chip *chip)
+{
+        int id;
+
+        for (id = 0; id < chip->ngpio; id++) {
+                if (test_bit(FLAG_IS_HOGGED, &chip->desc[id].flags))
+                        gpiochip_free_own_desc(&chip->desc[id]);
+        }
+}
+
+/**
  * gpiod_put - dispose of a GPIO descriptor
  * @desc:       GPIO descriptor to dispose of
  *
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 550a5eafbd38..cadba26c45a6 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -78,6 +78,7 @@ struct gpio_desc {
 #define FLAG_OPEN_SOURCE 8      /* Gpio is open source type */
 #define FLAG_USED_AS_IRQ 9      /* GPIO is connected to an IRQ */
 #define FLAG_SYSFS_DIR  10      /* show sysfs direction attribute */
+#define FLAG_IS_HOGGED  11      /* GPIO is hogged */
 
 #define ID_SHIFT        16      /* add new flags before this one */
 
@@ -89,6 +90,8 @@ struct gpio_desc {
 
 int gpiod_request(struct gpio_desc *desc, const char *label);
 void gpiod_free(struct gpio_desc *desc);
+int gpiod_hog(struct gpio_desc *desc, const char *name,
+                unsigned long lflags, enum gpiod_flags dflags);
 
 /*
  * Return the GPIO number of the passed descriptor relative to its chip