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>

2 files changed, 46 insertions, 7 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e14eb88bbe8d..453ac77771ca 100644
--- a/drivers/gpio/gpiolib.c
+++ b/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);
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 2034e691c7ab..b562f95cdc2f 100644
--- a/include/asm-generic/gpio.h
+++ b/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);