1 files changed, 45 insertions, 7 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 623fcd9b547a..2ba6127c4fae 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -80,6 +80,33 @@ static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
         return gpio_desc[gpio].chip;
 }
 
+/* dynamic allocation of GPIOs, e.g. on a hotplugged device */
+static int gpiochip_find_base(int ngpio)
+{
+        int i;
+        int spare = 0;
+        int base = -ENOSPC;
+
+        for (i = ARCH_NR_GPIOS - 1; i >= 0 ; i--) {
+                struct gpio_chip *chip = gpio_desc[i].chip;
+
+                if (!chip) {
+                        spare++;
+                        if (spare == ngpio) {
+                                base = i;
+                                break;
+                        }
+                } else {
+                        spare = 0;
+                        i -= chip->ngpio - 1;
+                }
+        }
+
+        if (gpio_is_valid(base))
+                pr_debug("%s: found new base at %d\n", __func__, base);
+        return base;
+}
+
 /**
  * gpiochip_add() - register a gpio_chip
  * @chip: the chip to register, with chip->base initialized
@@ -88,38 +115,49 @@ static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
  * Returns a negative errno if the chip can't be registered, such as
  * because the chip->base is invalid or already associated with a
  * different chip.  Otherwise it returns zero as a success code.
+ *
+ * If chip->base is negative, this requests dynamic assignment of
+ * a range of valid GPIOs.
  */
 int gpiochip_add(struct gpio_chip *chip)
 {
         unsigned long   flags;
         int             status = 0;
         unsigned        id;
+        int             base = chip->base;
 
-        /* NOTE chip->base negative is reserved to mean a request for
-         * dynamic allocation.  We don't currently support that.
-         */
-
-        if (chip->base < 0 || !gpio_is_valid(chip->base  + chip->ngpio)) {
+        if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio))
+                        && base >= 0) {
                 status = -EINVAL;
                 goto fail;
         }
 
         spin_lock_irqsave(&gpio_lock, flags);
 
+        if (base < 0) {
+                base = gpiochip_find_base(chip->ngpio);
+                if (base < 0) {
+                        status = base;
+                        goto fail_unlock;
+                }
+                chip->base = base;
+        }
+
         /* these GPIO numbers must not be managed by another gpio_chip */
-        for (id = chip->base; id < chip->base + chip->ngpio; id++) {
+        for (id = base; id < base + chip->ngpio; id++) {
                 if (gpio_desc[id].chip != NULL) {
                         status = -EBUSY;
                         break;
                 }
         }
         if (status == 0) {
-                for (id = chip->base; id < chip->base + chip->ngpio; id++) {
+                for (id = base; id < base + chip->ngpio; id++) {
                         gpio_desc[id].chip = chip;
                         gpio_desc[id].flags = 0;
                 }
         }
 
+fail_unlock:
         spin_unlock_irqrestore(&gpio_lock, flags);
 fail:
         /* failures here can mean systems won't boot... */