+/* 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_desc *desc = &gpio_desc[i];
+ struct gpio_chip *chip = desc->chip;
+
+ if (!chip && !test_bit(FLAG_RESERVED, &desc->flags)) {
+ spare++;
+ if (spare == ngpio) {
+ base = i;
+ break;
+ }
+ } else {
+ spare = 0;
+ if (chip)
+ i -= chip->ngpio - 1;
+ }
+ }
+
+ if (gpio_is_valid(base))
+ pr_debug("%s: found new base at %d\n", __func__, base);
+ return base;
+}
+
+/**
+ * gpiochip_reserve() - reserve range of gpios to use with platform code only
+ * @start: starting gpio number
+ * @ngpio: number of gpios to reserve
+ * Context: platform init, potentially before irqs or kmalloc will work
+ *
+ * Returns a negative errno if any gpio within the range is already reserved
+ * or registered, else returns zero as a success code. Use this function
+ * to mark a range of gpios as unavailable for dynamic gpio number allocation,
+ * for example because its driver support is not yet loaded.
+ */
+int __init gpiochip_reserve(int start, int ngpio)
+{
+ int ret = 0;
+ unsigned long flags;
+ int i;
+
+ if (!gpio_is_valid(start) || !gpio_is_valid(start + ngpio - 1))
+ return -EINVAL;
+
+ spin_lock_irqsave(&gpio_lock, flags);
+
+ for (i = start; i < start + ngpio; i++) {
+ struct gpio_desc *desc = &gpio_desc[i];
+
+ if (desc->chip || test_bit(FLAG_RESERVED, &desc->flags)) {
+ ret = -EBUSY;
+ goto err;
+ }
+
+ set_bit(FLAG_RESERVED, &desc->flags);
+ }
+
+ pr_debug("%s: reserved gpios from %d to %d\n",
+ __func__, start, start + ngpio - 1);
+err:
+ spin_unlock_irqrestore(&gpio_lock, flags);
+
+ return ret;
+}
+