gpiolib: link all gpio_chips using a list

Add a list member to gpio_chip that allows all chips to be parsed
quickly. The current method requires parsing the entire GPIO integer
space, which is painfully slow. Using a list makes many chip operations
that involve lookup or parsing faster, and also simplifies the code. It
is also necessary to eventually get rid of the global gpio_desc[] array.

The list of gpio_chips is always ordered by base GPIO number to ensure
chips traversal is done in the right order.
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/gpio/gpiolib.c

@@ -3,6 +3,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/spinlock.h>
+#include <linux/list.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/debugfs.h>
@@ -71,6 +72,8 @@ struct gpio_desc {
 };
 static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];
 
+static LIST_HEAD(gpio_chips);
+
 #ifdef CONFIG_GPIO_SYSFS
 static DEFINE_IDR(dirent_idr);
 #endif
@@ -1014,6 +1017,43 @@ static inline void gpiochip_unexport(struct gpio_chip *chip)
 
 #endif /* CONFIG_GPIO_SYSFS */
 
+/*
+ * Add a new chip to the global chips list, keeping the list of chips sorted
+ * by base order.
+ *
+ * Return -EBUSY if the new chip overlaps with some other chip's integer
+ * space.
+ */
+static int gpiochip_add_to_list(struct gpio_chip *chip)
+{
+	struct list_head *pos = &gpio_chips;
+	struct gpio_chip *_chip;
+	int err = 0;
+
+	/* find where to insert our chip */
+	list_for_each(pos, &gpio_chips) {
+		_chip = list_entry(pos, struct gpio_chip, list);
+		/* shall we insert before _chip? */
+		if (_chip->base >= chip->base + chip->ngpio)
+			break;
+	}
+
+	/* are we stepping on the chip right before? */
+	if (pos != &gpio_chips && pos->prev != &gpio_chips) {
+		_chip = list_entry(pos->prev, struct gpio_chip, list);
+		if (_chip->base + _chip->ngpio > chip->base) {
+			dev_err(chip->dev,
+			       "GPIO integer space overlap, cannot add chip\n");
+			err = -EBUSY;
+		}
+	}
+
+	if (!err)
+		list_add_tail(&chip->list, pos);
+
+	return err;
+}
+
 /**
  * gpiochip_add() - register a gpio_chip
  * @chip: the chip to register, with chip->base initialized
@@ -1055,13 +1095,8 @@ int gpiochip_add(struct gpio_chip *chip)
 		chip->base = base;
 	}
 
-	/* these GPIO numbers must not be managed by another gpio_chip */
-	for (id = base; id < base + chip->ngpio; id++) {
-		if (gpio_desc[id].chip != NULL) {
-			status = -EBUSY;
-			break;
-		}
-	}
+	status = gpiochip_add_to_list(chip);
+
 	if (status == 0) {
 		for (id = base; id < base + chip->ngpio; id++) {
 			gpio_desc[id].chip = chip;
@@ -1135,6 +1170,8 @@ int gpiochip_remove(struct gpio_chip *chip)
 	if (status == 0) {
 		for (id = chip->base; id < chip->base + chip->ngpio; id++)
 			gpio_desc[id].chip = NULL;
+
+		list_del(&chip->list);
 	}
 
 	spin_unlock_irqrestore(&gpio_lock, flags);

include/asm-generic/gpio.h

@@ -53,6 +53,7 @@ struct device_node;
  * @label: for diagnostics
  * @dev: optional device providing the GPIOs
  * @owner: helps prevent removal of modules exporting active GPIOs
+ * @list: links gpio_chips together for traversal
  * @request: optional hook for chip-specific activation, such as
  *	enabling module power and clock; may sleep
  * @free: optional hook for chip-specific deactivation, such as
@@ -98,6 +99,7 @@ struct gpio_chip {
 	const char		*label;
 	struct device		*dev;
 	struct module		*owner;
+	struct list_head        list;
 
 	int			(*request)(struct gpio_chip *chip,
 						unsigned offset);