gpio: sysfs interface

This adds a simple sysfs interface for GPIOs.

    /sys/class/gpio
    	/export ... asks the kernel to export a GPIO to userspace
    	/unexport ... to return a GPIO to the kernel
        /gpioN ... for each exported GPIO #N
	    /value ... always readable, writes fail for input GPIOs
	    /direction ... r/w as: in, out (default low); write high, low
	/gpiochipN ... for each gpiochip; #N is its first GPIO
	    /base ... (r/o) same as N
	    /label ... (r/o) descriptive, not necessarily unique
	    /ngpio ... (r/o) number of GPIOs; numbered N .. N+(ngpio - 1)

GPIOs claimed by kernel code may be exported by its owner using a new
gpio_export() call, which should be most useful for driver debugging.
Such exports may optionally be done without a "direction" attribute.

Userspace may ask to take over a GPIO by writing to a sysfs control file,
helping to cope with incomplete board support or other "one-off"
requirements that don't merit full kernel support:

  echo 23 > /sys/class/gpio/export
	... will gpio_request(23, "sysfs") and gpio_export(23);
	use /sys/class/gpio/gpio-23/direction to (re)configure it,
	when that GPIO can be used as both input and output.
  echo 23 > /sys/class/gpio/unexport
	... will gpio_free(23), when it was exported as above

The extra D-space footprint is a few hundred bytes, except for the sysfs
resources associated with each exported GPIO.  The additional I-space
footprint is about two thirds of the current size of gpiolib (!).  Since
no /dev node creation is involved, no "udev" support is needed.

Related changes:

  * This adds a device pointer to "struct gpio_chip".  When GPIO
    providers initialize that, sysfs gpio class devices become children of
    that device instead of being "virtual" devices.

  * The (few) gpio_chip providers which have such a device node have
    been updated.

  * Some gpio_chip drivers also needed to update their module "owner"
    field ...  for which missing kerneldoc was added.

  * Some gpio_chips don't support input GPIOs.  Those GPIOs are now
    flagged appropriately when the chip is registered.

Based on previous patches, and discussion both on and off LKML.

A Documentation/ABI/testing/sysfs-gpio update is ready to submit once this
merges to mainline.

[akpm@linux-foundation.org: a few maintenance build fixes]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Cc: Greg KH <greg@kroah.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 523 insertions, 13 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index beaf6b3a37d..8d2940517c9 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2,8 +2,11 @@
 #include <linux/module.h>
 #include <linux/irq.h>
 #include <linux/spinlock.h>
-
-#include <asm/gpio.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/gpio.h>
 
 
 /* Optional implementation infrastructure for GPIO interfaces.
@@ -44,6 +47,8 @@ struct gpio_desc {
 #define FLAG_REQUESTED  0
 #define FLAG_IS_OUT     1
 #define FLAG_RESERVED   2
+#define FLAG_EXPORT     3       /* protected by sysfs_lock */
+#define FLAG_SYSFS      4       /* exported via /sys/class/gpio/control */
 
 #ifdef CONFIG_DEBUG_FS
         const char              *label;
@@ -151,6 +156,482 @@ err:
         return ret;
 }
 
+#ifdef CONFIG_GPIO_SYSFS
+
+/* lock protects against unexport_gpio() being called while
+ * sysfs files are active.
+ */
+static DEFINE_MUTEX(sysfs_lock);
+
+/*
+ * /sys/class/gpio/gpioN... only for GPIOs that are exported
+ *   /direction
+ *      * MAY BE OMITTED if kernel won't allow direction changes
+ *      * is read/write as "in" or "out"
+ *      * may also be written as "high" or "low", initializing
+ *        output value as specified ("out" implies "low")
+ *   /value
+ *      * always readable, subject to hardware behavior
+ *      * may be writable, as zero/nonzero
+ *
+ * REVISIT there will likely be an attribute for configuring async
+ * notifications, e.g. to specify polling interval or IRQ trigger type
+ * that would for example trigger a poll() on the "value".
+ */
+
+static ssize_t gpio_direction_show(struct device *dev,
+                struct device_attribute *attr, char *buf)
+{
+        const struct gpio_desc  *desc = dev_get_drvdata(dev);
+        ssize_t                 status;
+
+        mutex_lock(&sysfs_lock);
+
+        if (!test_bit(FLAG_EXPORT, &desc->flags))
+                status = -EIO;
+        else
+                status = sprintf(buf, "%s\n",
+                        test_bit(FLAG_IS_OUT, &desc->flags)
+                                ? "out" : "in");
+
+        mutex_unlock(&sysfs_lock);
+        return status;
+}
+
+static ssize_t gpio_direction_store(struct device *dev,
+                struct device_attribute *attr, const char *buf, size_t size)
+{
+        const struct gpio_desc  *desc = dev_get_drvdata(dev);
+        unsigned                gpio = desc - gpio_desc;
+        ssize_t                 status;
+
+        mutex_lock(&sysfs_lock);
+
+        if (!test_bit(FLAG_EXPORT, &desc->flags))
+                status = -EIO;
+        else if (sysfs_streq(buf, "high"))
+                status = gpio_direction_output(gpio, 1);
+        else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
+                status = gpio_direction_output(gpio, 0);
+        else if (sysfs_streq(buf, "in"))
+                status = gpio_direction_input(gpio);
+        else
+                status = -EINVAL;
+
+        mutex_unlock(&sysfs_lock);
+        return status ? : size;
+}
+
+static const DEVICE_ATTR(direction, 0644,
+                gpio_direction_show, gpio_direction_store);
+
+static ssize_t gpio_value_show(struct device *dev,
+                struct device_attribute *attr, char *buf)
+{
+        const struct gpio_desc  *desc = dev_get_drvdata(dev);
+        unsigned                gpio = desc - gpio_desc;
+        ssize_t                 status;
+
+        mutex_lock(&sysfs_lock);
+
+        if (!test_bit(FLAG_EXPORT, &desc->flags))
+                status = -EIO;
+        else
+                status = sprintf(buf, "%d\n", gpio_get_value_cansleep(gpio));
+
+        mutex_unlock(&sysfs_lock);
+        return status;
+}
+
+static ssize_t gpio_value_store(struct device *dev,
+                struct device_attribute *attr, const char *buf, size_t size)
+{
+        const struct gpio_desc  *desc = dev_get_drvdata(dev);
+        unsigned                gpio = desc - gpio_desc;
+        ssize_t                 status;
+
+        mutex_lock(&sysfs_lock);
+
+        if (!test_bit(FLAG_EXPORT, &desc->flags))
+                status = -EIO;
+        else if (!test_bit(FLAG_IS_OUT, &desc->flags))
+                status = -EPERM;
+        else {
+                long            value;
+
+                status = strict_strtol(buf, 0, &value);
+                if (status == 0) {
+                        gpio_set_value_cansleep(gpio, value != 0);
+                        status = size;
+                }
+        }
+
+        mutex_unlock(&sysfs_lock);
+        return status;
+}
+
+static /*const*/ DEVICE_ATTR(value, 0644,
+                gpio_value_show, gpio_value_store);
+
+static const struct attribute *gpio_attrs[] = {
+        &dev_attr_direction.attr,
+        &dev_attr_value.attr,
+        NULL,
+};
+
+static const struct attribute_group gpio_attr_group = {
+        .attrs = (struct attribute **) gpio_attrs,
+};
+
+/*
+ * /sys/class/gpio/gpiochipN/
+ *   /base ... matching gpio_chip.base (N)
+ *   /label ... matching gpio_chip.label
+ *   /ngpio ... matching gpio_chip.ngpio
+ */
+
+static ssize_t chip_base_show(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+        const struct gpio_chip  *chip = dev_get_drvdata(dev);
+
+        return sprintf(buf, "%d\n", chip->base);
+}
+static DEVICE_ATTR(base, 0444, chip_base_show, NULL);
+
+static ssize_t chip_label_show(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+        const struct gpio_chip  *chip = dev_get_drvdata(dev);
+
+        return sprintf(buf, "%s\n", chip->label ? : "");
+}
+static DEVICE_ATTR(label, 0444, chip_label_show, NULL);
+
+static ssize_t chip_ngpio_show(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+        const struct gpio_chip  *chip = dev_get_drvdata(dev);
+
+        return sprintf(buf, "%u\n", chip->ngpio);
+}
+static DEVICE_ATTR(ngpio, 0444, chip_ngpio_show, NULL);
+
+static const struct attribute *gpiochip_attrs[] = {
+        &dev_attr_base.attr,
+        &dev_attr_label.attr,
+        &dev_attr_ngpio.attr,
+        NULL,
+};
+
+static const struct attribute_group gpiochip_attr_group = {
+        .attrs = (struct attribute **) gpiochip_attrs,
+};
+
+/*
+ * /sys/class/gpio/export ... write-only
+ *      integer N ... number of GPIO to export (full access)
+ * /sys/class/gpio/unexport ... write-only
+ *      integer N ... number of GPIO to unexport
+ */
+static ssize_t export_store(struct class *class, const char *buf, size_t len)
+{
+        long    gpio;
+        int     status;
+
+        status = strict_strtol(buf, 0, &gpio);
+        if (status < 0)
+                goto done;
+
+        /* No extra locking here; FLAG_SYSFS just signifies that the
+         * request and export were done by on behalf of userspace, so
+         * they may be undone on its behalf too.
+         */
+
+        status = gpio_request(gpio, "sysfs");
+        if (status < 0)
+                goto done;
+
+        status = gpio_export(gpio, true);
+        if (status < 0)
+                gpio_free(gpio);
+        else
+                set_bit(FLAG_SYSFS, &gpio_desc[gpio].flags);
+
+done:
+        if (status)
+                pr_debug("%s: status %d\n", __func__, status);
+        return status ? : len;
+}
+
+static ssize_t unexport_store(struct class *class, const char *buf, size_t len)
+{
+        long    gpio;
+        int     status;
+
+        status = strict_strtol(buf, 0, &gpio);
+        if (status < 0)
+                goto done;
+
+        status = -EINVAL;
+
+        /* reject bogus commands (gpio_unexport ignores them) */
+        if (!gpio_is_valid(gpio))
+                goto done;
+
+        /* No extra locking here; FLAG_SYSFS just signifies that the
+         * request and export were done by on behalf of userspace, so
+         * they may be undone on its behalf too.
+         */
+        if (test_and_clear_bit(FLAG_SYSFS, &gpio_desc[gpio].flags)) {
+                status = 0;
+                gpio_free(gpio);
+        }
+done:
+        if (status)
+                pr_debug("%s: status %d\n", __func__, status);
+        return status ? : len;
+}
+
+static struct class_attribute gpio_class_attrs[] = {
+        __ATTR(export, 0200, NULL, export_store),
+        __ATTR(unexport, 0200, NULL, unexport_store),
+        __ATTR_NULL,
+};
+
+static struct class gpio_class = {
+        .name =         "gpio",
+        .owner =        THIS_MODULE,
+
+        .class_attrs =  gpio_class_attrs,
+};
+
+
+/**
+ * gpio_export - export a GPIO through sysfs
+ * @gpio: gpio to make available, already requested
+ * @direction_may_change: true if userspace may change gpio direction
+ * Context: arch_initcall or later
+ *
+ * When drivers want to make a GPIO accessible to userspace after they
+ * have requested it -- perhaps while debugging, or as part of their
+ * public interface -- they may use this routine.  If the GPIO can
+ * change direction (some can't) and the caller allows it, userspace
+ * will see "direction" sysfs attribute which may be used to change
+ * the gpio's direction.  A "value" attribute will always be provided.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpio_export(unsigned gpio, bool direction_may_change)
+{
+        unsigned long           flags;
+        struct gpio_desc        *desc;
+        int                     status = -EINVAL;
+
+        /* can't export until sysfs is available ... */
+        if (!gpio_class.p) {
+                pr_debug("%s: called too early!\n", __func__);
+                return -ENOENT;
+        }
+
+        if (!gpio_is_valid(gpio))
+                goto done;
+
+        mutex_lock(&sysfs_lock);
+
+        spin_lock_irqsave(&gpio_lock, flags);
+        desc = &gpio_desc[gpio];
+        if (test_bit(FLAG_REQUESTED, &desc->flags)
+                        && !test_bit(FLAG_EXPORT, &desc->flags)) {
+                status = 0;
+                if (!desc->chip->direction_input
+                                || !desc->chip->direction_output)
+                        direction_may_change = false;
+        }
+        spin_unlock_irqrestore(&gpio_lock, flags);
+
+        if (status == 0) {
+                struct device   *dev;
+
+                dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
+                                        desc, "gpio%d", gpio);
+                if (dev) {
+                        if (direction_may_change)
+                                status = sysfs_create_group(&dev->kobj,
+                                                &gpio_attr_group);
+                        else
+                                status = device_create_file(dev,
+                                                &dev_attr_value);
+                        if (status != 0)
+                                device_unregister(dev);
+                } else
+                        status = -ENODEV;
+                if (status == 0)
+                        set_bit(FLAG_EXPORT, &desc->flags);
+        }
+
+        mutex_unlock(&sysfs_lock);
+
+done:
+        if (status)
+                pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
+
+        return status;
+}
+EXPORT_SYMBOL_GPL(gpio_export);
+
+static int match_export(struct device *dev, void *data)
+{
+        return dev_get_drvdata(dev) == data;
+}
+
+/**
+ * gpio_unexport - reverse effect of gpio_export()
+ * @gpio: gpio to make unavailable
+ *
+ * This is implicit on gpio_free().
+ */
+void gpio_unexport(unsigned gpio)
+{
+        struct gpio_desc        *desc;
+        int                     status = -EINVAL;
+
+        if (!gpio_is_valid(gpio))
+                goto done;
+
+        mutex_lock(&sysfs_lock);
+
+        desc = &gpio_desc[gpio];
+        if (test_bit(FLAG_EXPORT, &desc->flags)) {
+                struct device   *dev = NULL;
+
+                dev = class_find_device(&gpio_class, NULL, desc, match_export);
+                if (dev) {
+                        clear_bit(FLAG_EXPORT, &desc->flags);
+                        put_device(dev);
+                        device_unregister(dev);
+                        status = 0;
+                } else
+                        status = -ENODEV;
+        }
+
+        mutex_unlock(&sysfs_lock);
+done:
+        if (status)
+                pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
+}
+EXPORT_SYMBOL_GPL(gpio_unexport);
+
+static int gpiochip_export(struct gpio_chip *chip)
+{
+        int             status;
+        struct device   *dev;
+
+        /* Many systems register gpio chips for SOC support very early,
+         * before driver model support is available.  In those cases we
+         * export this later, in gpiolib_sysfs_init() ... here we just
+         * verify that _some_ field of gpio_class got initialized.
+         */
+        if (!gpio_class.p)
+                return 0;
+
+        /* use chip->base for the ID; it's already known to be unique */
+        mutex_lock(&sysfs_lock);
+        dev = device_create(&gpio_class, chip->dev, MKDEV(0, 0), chip,
+                                "gpiochip%d", chip->base);
+        if (dev) {
+                status = sysfs_create_group(&dev->kobj,
+                                &gpiochip_attr_group);
+        } else
+                status = -ENODEV;
+        chip->exported = (status == 0);
+        mutex_unlock(&sysfs_lock);
+
+        if (status) {
+                unsigned long   flags;
+                unsigned        gpio;
+
+                spin_lock_irqsave(&gpio_lock, flags);
+                gpio = chip->base;
+                while (gpio_desc[gpio].chip == chip)
+                        gpio_desc[gpio++].chip = NULL;
+                spin_unlock_irqrestore(&gpio_lock, flags);
+
+                pr_debug("%s: chip %s status %d\n", __func__,
+                                chip->label, status);
+        }
+
+        return status;
+}
+
+static void gpiochip_unexport(struct gpio_chip *chip)
+{
+        int                     status;
+        struct device           *dev;
+
+        mutex_lock(&sysfs_lock);
+        dev = class_find_device(&gpio_class, NULL, chip, match_export);
+        if (dev) {
+                put_device(dev);
+                device_unregister(dev);
+                chip->exported = 0;
+                status = 0;
+        } else
+                status = -ENODEV;
+        mutex_unlock(&sysfs_lock);
+
+        if (status)
+                pr_debug("%s: chip %s status %d\n", __func__,
+                                chip->label, status);
+}
+
+static int __init gpiolib_sysfs_init(void)
+{
+        int             status;
+        unsigned long   flags;
+        unsigned        gpio;
+
+        status = class_register(&gpio_class);
+        if (status < 0)
+                return status;
+
+        /* Scan and register the gpio_chips which registered very
+         * early (e.g. before the class_register above was called).
+         *
+         * We run before arch_initcall() so chip->dev nodes can have
+         * registered, and so arch_initcall() can always gpio_export().
+         */
+        spin_lock_irqsave(&gpio_lock, flags);
+        for (gpio = 0; gpio < ARCH_NR_GPIOS; gpio++) {
+                struct gpio_chip        *chip;
+
+                chip = gpio_desc[gpio].chip;
+                if (!chip || chip->exported)
+                        continue;
+
+                spin_unlock_irqrestore(&gpio_lock, flags);
+                status = gpiochip_export(chip);
+                spin_lock_irqsave(&gpio_lock, flags);
+        }
+        spin_unlock_irqrestore(&gpio_lock, flags);
+
+
+        return status;
+}
+postcore_initcall(gpiolib_sysfs_init);
+
+#else
+static inline int gpiochip_export(struct gpio_chip *chip)
+{
+        return 0;
+}
+
+static inline void gpiochip_unexport(struct gpio_chip *chip)
+{
+}
+
+#endif /* CONFIG_GPIO_SYSFS */
+
 /**
  * gpiochip_add() - register a gpio_chip
  * @chip: the chip to register, with chip->base initialized
@@ -160,6 +641,11 @@ err:
  * because the chip->base is invalid or already associated with a
  * different chip.  Otherwise it returns zero as a success code.
  *
+ * When gpiochip_add() is called very early during boot, so that GPIOs
+ * can be freely used, the chip->dev device must be registered before
+ * the gpio framework's arch_initcall().  Otherwise sysfs initialization
+ * for GPIOs will fail rudely.
+ *
  * If chip->base is negative, this requests dynamic assignment of
  * a range of valid GPIOs.
  */
@@ -182,7 +668,7 @@ int gpiochip_add(struct gpio_chip *chip)
                 base = gpiochip_find_base(chip->ngpio);
                 if (base < 0) {
                         status = base;
-                        goto fail_unlock;
+                        goto unlock;
                 }
                 chip->base = base;
         }
@@ -197,12 +683,23 @@ int gpiochip_add(struct gpio_chip *chip)
         if (status == 0) {
                 for (id = base; id < base + chip->ngpio; id++) {
                         gpio_desc[id].chip = chip;
-                        gpio_desc[id].flags = 0;
+
+                        /* REVISIT:  most hardware initializes GPIOs as
+                         * inputs (often with pullups enabled) so power
+                         * usage is minimized.  Linux code should set the
+                         * gpio direction first thing; but until it does,
+                         * we may expose the wrong direction in sysfs.
+                         */
+                        gpio_desc[id].flags = !chip->direction_input
+                                ? (1 << FLAG_IS_OUT)
+                                : 0;
                 }
         }
 
-fail_unlock:
+unlock:
         spin_unlock_irqrestore(&gpio_lock, flags);
+        if (status == 0)
+                status = gpiochip_export(chip);
 fail:
         /* failures here can mean systems won't boot... */
         if (status)
@@ -239,6 +736,10 @@ int gpiochip_remove(struct gpio_chip *chip)
         }
 
         spin_unlock_irqrestore(&gpio_lock, flags);
+
+        if (status == 0)
+                gpiochip_unexport(chip);
+
         return status;
 }
 EXPORT_SYMBOL_GPL(gpiochip_remove);
@@ -296,6 +797,8 @@ void gpio_free(unsigned gpio)
                 return;
         }
 
+        gpio_unexport(gpio);
+
         spin_lock_irqsave(&gpio_lock, flags);
 
         desc = &gpio_desc[gpio];
@@ -534,10 +1037,6 @@ EXPORT_SYMBOL_GPL(gpio_set_value_cansleep);
 
 #ifdef CONFIG_DEBUG_FS
 
-#include <linux/debugfs.h>
-#include <linux/seq_file.h>
-
-
 static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
 {
         unsigned                i;
@@ -614,17 +1113,28 @@ static int gpiolib_show(struct seq_file *s, void *unused)
         /* 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)
                         continue;
                 chip = gpio_desc[gpio].chip;
                 if (!chip)
                         continue;
 
-                seq_printf(s, "%sGPIOs %d-%d, %s%s:\n",
+                seq_printf(s, "%sGPIOs %d-%d",
                                 started ? "\n" : "",
-                                chip->base, chip->base + chip->ngpio - 1,
-                                chip->label ? : "generic",
-                                chip->can_sleep ? ", can sleep" : "");
+                                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->bus_id);
+                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);