gpio: better lookup method for platform GPIOs

Change the format of the platform GPIO lookup tables to make them less
confusing and improve lookup efficiency.

The previous format was a single linked-list that required to compare
the device name and function ID of every single GPIO defined for each
lookup. Switch that to a list of per-device tables, so that the lookup
can be done in two steps, omitting the GPIOs that are not relevant for a
particular device.

The matching rules are now defined as follows:
- The device name must match *exactly*, and can be NULL for GPIOs not
  assigned to a particular device,
- If the function ID in the lookup table is NULL, the con_id argument of
  gpiod_get() will not be used for lookup. However, if it is defined, it
  must match exactly.
- The index must always match.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

3 files changed, 85 insertions, 72 deletions

diff --git a/Documentation/gpio/board.txt b/Documentation/gpio/board.txt
index 0d03506f2cc5..ba169faad5c6 100644
--- a/Documentation/gpio/board.txt
+++ b/Documentation/gpio/board.txt
@@ -72,10 +72,11 @@ where
 
   - chip_label is the label of the gpiod_chip instance providing the GPIO
   - chip_hwnum is the hardware number of the GPIO within the chip
-  - dev_id is the identifier of the device that will make use of this GPIO. If
-        NULL, the GPIO will be available to all devices.
+  - dev_id is the identifier of the device that will make use of this GPIO. It
+        can be NULL, in which case it will be matched for calls to gpiod_get()
+        with a NULL device.
   - con_id is the name of the GPIO function from the device point of view. It
-        can be NULL.
+        can be NULL, in which case it will match any function.
   - idx is the index of the GPIO within the function.
   - flags is defined to specify the following properties:
         * GPIOF_ACTIVE_LOW      - to configure the GPIO as active-low
@@ -86,18 +87,23 @@ In the future, these flags might be extended to support more properties.
 
 Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
 
-A lookup table can then be defined as follows:
+A lookup table can then be defined as follows, with an empty entry defining its
+end:
 
-        struct gpiod_lookup gpios_table[] = {
-        GPIO_LOOKUP_IDX("gpio.0", 15, "foo.0", "led", 0, GPIO_ACTIVE_HIGH),
-        GPIO_LOOKUP_IDX("gpio.0", 16, "foo.0", "led", 1, GPIO_ACTIVE_HIGH),
-        GPIO_LOOKUP_IDX("gpio.0", 17, "foo.0", "led", 2, GPIO_ACTIVE_HIGH),
-        GPIO_LOOKUP("gpio.0", 1, "foo.0", "power", GPIO_ACTIVE_LOW),
-        };
+struct gpiod_lookup_table gpios_table = {
+        .dev_id = "foo.0",
+        .table = {
+                GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
+                GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
+                GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
+                GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
+                { },
+        },
+};
 
 And the table can be added by the board code as follows:
 
-        gpiod_add_table(gpios_table, ARRAY_SIZE(gpios_table));
+        gpiod_add_lookup_table(&gpios_table);
 
 The driver controlling "foo.0" will then be able to obtain its GPIOs as follows:
 
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 44a232701179..4eb262a31777 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2260,18 +2260,14 @@ void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
 EXPORT_SYMBOL_GPL(gpiod_set_value_cansleep);
 
 /**
- * gpiod_add_table() - register GPIO device consumers
- * @table: array of consumers to register
- * @num: number of consumers in table
+ * gpiod_add_lookup_table() - register GPIO device consumers
+ * @table: table of consumers to register
  */
-void gpiod_add_table(struct gpiod_lookup *table, size_t size)
+void gpiod_add_lookup_table(struct gpiod_lookup_table *table)
 {
         mutex_lock(&gpio_lookup_lock);
 
-        while (size--) {
-                list_add_tail(&table->list, &gpio_lookup_list);
-                table++;
-        }
+        list_add_tail(&table->list, &gpio_lookup_list);
 
         mutex_unlock(&gpio_lookup_lock);
 }
@@ -2327,72 +2323,84 @@ static struct gpio_desc *acpi_find_gpio(struct device *dev, const char *con_id,
         return desc;
 }
 
-static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
-                                    unsigned int idx,
-                                    enum gpio_lookup_flags *flags)
+static struct gpiod_lookup_table *gpiod_find_lookup_table(struct device *dev)
 {
         const char *dev_id = dev ? dev_name(dev) : NULL;
-        struct gpio_desc *desc = ERR_PTR(-ENODEV);
-        unsigned int match, best = 0;
-        struct gpiod_lookup *p;
+        struct gpiod_lookup_table *table;
 
         mutex_lock(&gpio_lookup_lock);
 
-        list_for_each_entry(p, &gpio_lookup_list, list) {
-                match = 0;
+        list_for_each_entry(table, &gpio_lookup_list, list) {
+                if (table->dev_id && dev_id) {
+                        /*
+                         * Valid strings on both ends, must be identical to have
+                         * a match
+                         */
+                        if (!strcmp(table->dev_id, dev_id))
+                                goto found;
+                } else {
+                        /*
+                         * One of the pointers is NULL, so both must be to have
+                         * a match
+                         */
+                        if (dev_id == table->dev_id)
+                                goto found;
+                }
+        }
+        table = NULL;
 
-                if (p->dev_id) {
-                        if (!dev_id || strcmp(p->dev_id, dev_id))
-                                continue;
+found:
+        mutex_unlock(&gpio_lookup_lock);
+        return table;
+}
 
-                        match += 2;
-                }
+static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
+                                    unsigned int idx,
+                                    enum gpio_lookup_flags *flags)
+{
+        struct gpio_desc *desc = ERR_PTR(-ENODEV);
+        struct gpiod_lookup_table *table;
+        struct gpiod_lookup *p;
 
-                if (p->con_id) {
-                        if (!con_id || strcmp(p->con_id, con_id))
-                                continue;
+        table = gpiod_find_lookup_table(dev);
+        if (!table)
+                return desc;
 
-                        match += 1;
-                }
+        for (p = &table->table[0]; p->chip_label; p++) {
+                struct gpio_chip *chip;
 
+                /* idx must always match exactly */
                 if (p->idx != idx)
                         continue;
 
-                if (match > best) {
-                        struct gpio_chip *chip;
-
-                        chip = find_chip_by_name(p->chip_label);
-
-                        if (!chip) {
-                                dev_warn(dev, "cannot find GPIO chip %s\n",
-                                         p->chip_label);
-                                continue;
-                        }
+                /* If the lookup entry has a con_id, require exact match */
+                if (p->con_id && (!con_id || strcmp(p->con_id, con_id)))
+                        continue;
 
-                        if (chip->ngpio <= p->chip_hwnum) {
-                                dev_warn(dev, "GPIO chip %s has %d GPIOs\n",
-                                         chip->label, chip->ngpio);
-                                continue;
-                        }
+                chip = find_chip_by_name(p->chip_label);
 
-                        desc = gpio_to_desc(chip->base + p->chip_hwnum);
-                        *flags = p->flags;
+                if (!chip) {
+                        dev_warn(dev, "cannot find GPIO chip %s\n",
+                                 p->chip_label);
+                        continue;
+                }
 
-                        if (match != 3)
-                                best = match;
-                        else
-                                break;
+                if (chip->ngpio <= p->chip_hwnum) {
+                        dev_warn(dev, "GPIO chip %s has %d GPIOs\n",
+                                 chip->label, chip->ngpio);
+                        continue;
                 }
-        }
 
-        mutex_unlock(&gpio_lookup_lock);
+                desc = gpiochip_offset_to_desc(chip, p->chip_hwnum);
+                *flags = p->flags;
+        }
 
         return desc;
 }
 
 /**
  * gpio_get - obtain a GPIO for a given GPIO function
- * @dev:        GPIO consumer
+ * @dev:        GPIO consumer, can be NULL for system-global GPIOs
  * @con_id:     function within the GPIO consumer
  *
  * Return the GPIO descriptor corresponding to the function con_id of device
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index c849676c6787..44c66b29a2d9 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -141,7 +141,6 @@ enum gpio_lookup_flags {
  * platform data.
  */
 struct gpiod_lookup {
-        struct list_head list;
         /*
          * name of the chip the GPIO belongs to
          */
@@ -151,10 +150,6 @@ struct gpiod_lookup {
          */
         u16 chip_hwnum;
         /*
-         * name of device that can claim this GPIO
-         */
-        const char *dev_id;
-        /*
          * name of the GPIO from the device's point of view
          */
         const char *con_id;
@@ -168,28 +163,32 @@ struct gpiod_lookup {
         enum gpio_lookup_flags flags;
 };
 
+struct gpiod_lookup_table {
+        struct list_head list;
+        const char *dev_id;
+        struct gpiod_lookup table[];
+};
+
 /*
  * Simple definition of a single GPIO under a con_id
  */
-#define GPIO_LOOKUP(_chip_label, _chip_hwnum, _dev_id, _con_id, _flags) \
-        GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _dev_id, _con_id, 0, _flags)
+#define GPIO_LOOKUP(_chip_label, _chip_hwnum, _con_id, _flags) \
+        GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _con_id, 0, _flags)
 
 /*
  * Use this macro if you need to have several GPIOs under the same con_id.
  * Each GPIO needs to use a different index and can be accessed using
  * gpiod_get_index()
  */
-#define GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _dev_id, _con_id, _idx, \
-                        _flags)                                           \
+#define GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _con_id, _idx, _flags)  \
 {                                                                         \
         .chip_label = _chip_label,                                        \
         .chip_hwnum = _chip_hwnum,                                        \
-        .dev_id = _dev_id,                                                \
         .con_id = _con_id,                                                \
         .idx = _idx,                                                      \
         .flags = _flags,                                                  \
 }
 
-void gpiod_add_table(struct gpiod_lookup *table, size_t size);
+void gpiod_add_lookup_table(struct gpiod_lookup_table *table);
 
 #endif