Currently GPIOs can only be referred to by GPIO controller and offset in
GPIO lookup tables.

Add support for looking them up by line name.
Rename gpiod_lookup.chip_label to gpiod_lookup.key, to make it clear
that this field can have two meanings, and update the kerneldoc and
GPIO_LOOKUP*() macros.

Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
Reviewed-by: Ulrich Hecht <uli+rene...@fpond.eu>
---
v4:
  - Add Reviewed-by,
  - Rename gpiod_lookup.chip_label.
  - Use U16_MAX instead of (u16)-1,

v3:
  - New.
---
 drivers/gpio/gpiolib.c       | 22 +++++++++++++++++-----
 include/linux/gpio/machine.h | 15 ++++++++-------
 2 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 114325b366ae33d5..48fc6cf9a020f4ff 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4457,7 +4457,7 @@ static struct gpio_desc *gpiod_find(struct device *dev, 
const char *con_id,
        if (!table)
                return desc;
 
-       for (p = &table->table[0]; p->chip_label; p++) {
+       for (p = &table->table[0]; p->key; p++) {
                struct gpio_chip *chip;
 
                /* idx must always match exactly */
@@ -4468,18 +4468,30 @@ static struct gpio_desc *gpiod_find(struct device *dev, 
const char *con_id,
                if (p->con_id && (!con_id || strcmp(p->con_id, con_id)))
                        continue;
 
-               chip = find_chip_by_name(p->chip_label);
+               if (p->chip_hwnum == U16_MAX) {
+                       desc = gpio_name_to_desc(p->key);
+                       if (desc) {
+                               *flags = p->flags;
+                               return desc;
+                       }
+
+                       dev_warn(dev, "cannot find GPIO line %s, deferring\n",
+                                p->key);
+                       return ERR_PTR(-EPROBE_DEFER);
+               }
+
+               chip = find_chip_by_name(p->key);
 
                if (!chip) {
                        /*
                         * As the lookup table indicates a chip with
-                        * p->chip_label should exist, assume it may
+                        * p->key should exist, assume it may
                         * still appear later and let the interested
                         * consumer be probed again or let the Deferred
                         * Probe infrastructure handle the error.
                         */
                        dev_warn(dev, "cannot find GPIO chip %s, deferring\n",
-                                p->chip_label);
+                                p->key);
                        return ERR_PTR(-EPROBE_DEFER);
                }
 
@@ -4510,7 +4522,7 @@ static int platform_gpio_count(struct device *dev, const 
char *con_id)
        if (!table)
                return -ENOENT;
 
-       for (p = &table->table[0]; p->chip_label; p++) {
+       for (p = &table->table[0]; p->key; p++) {
                if ((con_id && p->con_id && !strcmp(con_id, p->con_id)) ||
                    (!con_id && !p->con_id))
                        count++;
diff --git a/include/linux/gpio/machine.h b/include/linux/gpio/machine.h
index 1ebe5be05d5f81fa..84c66fbf54fd5811 100644
--- a/include/linux/gpio/machine.h
+++ b/include/linux/gpio/machine.h
@@ -20,8 +20,9 @@ enum gpio_lookup_flags {
 
 /**
  * struct gpiod_lookup - lookup table
- * @chip_label: name of the chip the GPIO belongs to
- * @chip_hwnum: hardware number (i.e. relative to the chip) of the GPIO
+ * @key: either the name of the chip the GPIO belongs to, or the GPIO line name
+ * @chip_hwnum: hardware number (i.e. relative to the chip) of the GPIO, or
+ *              U16_MAX to indicate that @key is a GPIO line name
  * @con_id: name of the GPIO from the device's point of view
  * @idx: index of the GPIO in case several GPIOs share the same name
  * @flags: bitmask of gpio_lookup_flags GPIO_* values
@@ -30,7 +31,7 @@ enum gpio_lookup_flags {
  * functions using platform data.
  */
 struct gpiod_lookup {
-       const char *chip_label;
+       const char *key;
        u16 chip_hwnum;
        const char *con_id;
        unsigned int idx;
@@ -63,17 +64,17 @@ struct gpiod_hog {
 /*
  * Simple definition of a single GPIO under a con_id
  */
-#define GPIO_LOOKUP(_chip_label, _chip_hwnum, _con_id, _flags) \
-       GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _con_id, 0, _flags)
+#define GPIO_LOOKUP(_key, _chip_hwnum, _con_id, _flags) \
+       GPIO_LOOKUP_IDX(_key, _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, _con_id, _idx, _flags)  \
+#define GPIO_LOOKUP_IDX(_key, _chip_hwnum, _con_id, _idx, _flags)         \
 {                                                                         \
-       .chip_label = _chip_label,                                        \
+       .key = _key,                                                      \
        .chip_hwnum = _chip_hwnum,                                        \
        .con_id = _con_id,                                                \
        .idx = _idx,                                                      \
-- 
2.17.1


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