gpiolib: Use seq_file's iterator interface

When dumping a collection of items via seq_file, it is recommended to
use the iterator interface. For the gpiolib debugfs interface this can
be done to dump each GPIO chip in turn.

Note that for gpiolib this is a little cumbersome because it does not
provide a list of registered GPIO chips and the only way to iterate is
over each GPIO individually. Once a chip is found, the number of GPIOs
it provides can be skipped as a small optimization.

This patch was requested by Arnd Bergmann here:

	http://article.gmane.org/gmane.linux.ports.tegra/3535

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Linus Walleij <linus.walleij@stericsson.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 74 insertions, 28 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index de0213c9d11c..5d6c71edc739 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1773,56 +1773,102 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
         }
 }
 
-static int gpiolib_show(struct seq_file *s, void *unused)
+static void *gpiolib_seq_start(struct seq_file *s, loff_t *pos)
 {
-        struct gpio_chip        *chip = NULL;
-        unsigned                gpio;
-        int                     started = 0;
+        struct gpio_chip *chip = NULL;
+        unsigned int gpio;
+        void *ret = NULL;
+        loff_t index = 0;
 
         /* REVISIT this isn't locked against gpio_chip removal ... */
 
         for (gpio = 0; gpio_is_valid(gpio); gpio++) {
-                struct device *dev;
-
-                if (chip == gpio_desc[gpio].chip)
+                if (gpio_desc[gpio].chip == chip)
                         continue;
+
                 chip = gpio_desc[gpio].chip;
                 if (!chip)
                         continue;
 
-                seq_printf(s, "%sGPIOs %d-%d",
-                                started ? "\n" : "",
-                                chip->base, chip->base + chip->ngpio - 1);
-                dev = chip->dev;
-                if (dev)
-                        seq_printf(s, ", %s/%s",
-                                dev->bus ? dev->bus->name : "no-bus",
-                                dev_name(dev));
-                if (chip->label)
-                        seq_printf(s, ", %s", chip->label);
-                if (chip->can_sleep)
-                        seq_printf(s, ", can sleep");
-                seq_printf(s, ":\n");
-
-                started = 1;
-                if (chip->dbg_show)
-                        chip->dbg_show(s, chip);
-                else
-                        gpiolib_dbg_show(s, chip);
+                if (index++ >= *pos) {
+                        ret = chip;
+                        break;
+                }
         }
+
+        s->private = "";
+
+        return ret;
+}
+
+static void *gpiolib_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+        struct gpio_chip *chip = v;
+        unsigned int gpio;
+        void *ret = NULL;
+
+        /* skip GPIOs provided by the current chip */
+        for (gpio = chip->base + chip->ngpio; gpio_is_valid(gpio); gpio++) {
+                chip = gpio_desc[gpio].chip;
+                if (chip) {
+                        ret = chip;
+                        break;
+                }
+        }
+
+        s->private = "\n";
+        ++*pos;
+
+        return ret;
+}
+
+static void gpiolib_seq_stop(struct seq_file *s, void *v)
+{
+}
+
+static int gpiolib_seq_show(struct seq_file *s, void *v)
+{
+        struct gpio_chip *chip = v;
+        struct device *dev;
+
+        seq_printf(s, "%sGPIOs %d-%d", (char *)s->private,
+                        chip->base, chip->base + chip->ngpio - 1);
+        dev = chip->dev;
+        if (dev)
+                seq_printf(s, ", %s/%s", dev->bus ? dev->bus->name : "no-bus",
+                        dev_name(dev));
+        if (chip->label)
+                seq_printf(s, ", %s", chip->label);
+        if (chip->can_sleep)
+                seq_printf(s, ", can sleep");
+        seq_printf(s, ":\n");
+
+        if (chip->dbg_show)
+                chip->dbg_show(s, chip);
+        else
+                gpiolib_dbg_show(s, chip);
+
         return 0;
 }
 
+static const struct seq_operations gpiolib_seq_ops = {
+        .start = gpiolib_seq_start,
+        .next = gpiolib_seq_next,
+        .stop = gpiolib_seq_stop,
+        .show = gpiolib_seq_show,
+};
+
 static int gpiolib_open(struct inode *inode, struct file *file)
 {
-        return single_open(file, gpiolib_show, NULL);
+        return seq_open(file, &gpiolib_seq_ops);
 }
 
 static const struct file_operations gpiolib_operations = {
+        .owner          = THIS_MODULE,
         .open           = gpiolib_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
-        .release        = single_release,
+        .release        = seq_release,
 };
 
 static int __init gpiolib_debugfs_init(void)