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[openwrt.git] / target / linux / generic-2.6 / patches-2.6.26 / 980-backport_gpio_sysfs_support.patch

From: David Brownell <dbrownell@users.sourceforge.net>
Date: Fri, 25 Jul 2008 08:46:07 +0000 (-0700)
Subject: gpio: sysfs interface
X-Git-Tag: v2.6.27-rc1~449
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=d8f388d8dc8d4f36539dd37c1fff62cc404ea0fc

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>
---

--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -347,15 +347,12 @@ necessarily be nonportable.
 Dynamic definition of GPIOs is not currently standard; for example, as
 a side effect of configuring an add-on board with some GPIO expanders.
 
-These calls are purely for kernel space, but a userspace API could be built
-on top of them.
-
 
 GPIO implementor's framework (OPTIONAL)
 =======================================
 As noted earlier, there is an optional implementation framework making it
 easier for platforms to support different kinds of GPIO controller using
-the same programming interface.
+the same programming interface.  This framework is called "gpiolib".
 
 As a debugging aid, if debugfs is available a /sys/kernel/debug/gpio file
 will be found there.  That will list all the controllers registered through
@@ -439,4 +436,120 @@ becomes available.  That may mean the de
 calls for that GPIO can work.  One way to address such dependencies is for
 such gpio_chip controllers to provide setup() and teardown() callbacks to
 board specific code; those board specific callbacks would register devices
-once all the necessary resources are available.
+once all the necessary resources are available, and remove them later when
+the GPIO controller device becomes unavailable.
+
+
+Sysfs Interface for Userspace (OPTIONAL)
+========================================
+Platforms which use the "gpiolib" implementors framework may choose to
+configure a sysfs user interface to GPIOs.  This is different from the
+debugfs interface, since it provides control over GPIO direction and
+value instead of just showing a gpio state summary.  Plus, it could be
+present on production systems without debugging support.
+
+Given approprate hardware documentation for the system, userspace could
+know for example that GPIO #23 controls the write protect line used to
+protect boot loader segments in flash memory.  System upgrade procedures
+may need to temporarily remove that protection, first importing a GPIO,
+then changing its output state, then updating the code before re-enabling
+the write protection.  In normal use, GPIO #23 would never be touched,
+and the kernel would have no need to know about it.
+
+Again depending on appropriate hardware documentation, on some systems
+userspace GPIO can be used to determine system configuration data that
+standard kernels won't know about.  And for some tasks, simple userspace
+GPIO drivers could be all that the system really needs.
+
+Note that standard kernel drivers exist for common "LEDs and Buttons"
+GPIO tasks:  "leds-gpio" and "gpio_keys", respectively.  Use those
+instead of talking directly to the GPIOs; they integrate with kernel
+frameworks better than your userspace code could.
+
+
+Paths in Sysfs
+--------------
+There are three kinds of entry in /sys/class/gpio:
+
+   -   Control interfaces used to get userspace control over GPIOs;
+
+   -   GPIOs themselves; and
+
+   -   GPIO controllers ("gpio_chip" instances).
+
+That's in addition to standard files including the "device" symlink.
+
+The control interfaces are write-only:
+
+    /sys/class/gpio/
+
+       "export" ... Userspace may ask the kernel to export control of
+               a GPIO to userspace by writing its number to this file.
+
+               Example:  "echo 19 > export" will create a "gpio19" node
+               for GPIO #19, if that's not requested by kernel code.
+
+       "unexport" ... Reverses the effect of exporting to userspace.
+
+               Example:  "echo 19 > unexport" will remove a "gpio19"
+               node exported using the "export" file.
+
+GPIO signals have paths like /sys/class/gpio/gpio42/ (for GPIO #42)
+and have the following read/write attributes:
+
+    /sys/class/gpio/gpioN/
+
+       "direction" ... reads as either "in" or "out".  This value may
+               normally be written.  Writing as "out" defaults to
+               initializing the value as low.  To ensure glitch free
+               operation, values "low" and "high" may be written to
+               configure the GPIO as an output with that initial value.
+
+               Note that this attribute *will not exist* if the kernel
+               doesn't support changing the direction of a GPIO, or
+               it was exported by kernel code that didn't explicitly
+               allow userspace to reconfigure this GPIO's direction.
+
+       "value" ... reads as either 0 (low) or 1 (high).  If the GPIO
+               is configured as an output, this value may be written;
+               any nonzero value is treated as high.
+
+GPIO controllers have paths like /sys/class/gpio/chipchip42/ (for the
+controller implementing GPIOs starting at #42) and have the following
+read-only attributes:
+
+    /sys/class/gpio/gpiochipN/
+
+       "base" ... same as N, the first GPIO managed by this chip
+
+       "label" ... provided for diagnostics (not always unique)
+
+       "ngpio" ... how many GPIOs this manges (N to N + ngpio - 1)
+
+Board documentation should in most cases cover what GPIOs are used for
+what purposes.  However, those numbers are not always stable; GPIOs on
+a daughtercard might be different depending on the base board being used,
+or other cards in the stack.  In such cases, you may need to use the
+gpiochip nodes (possibly in conjunction with schematics) to determine
+the correct GPIO number to use for a given signal.
+
+
+Exporting from Kernel code
+--------------------------
+Kernel code can explicitly manage exports of GPIOs which have already been
+requested using gpio_request():
+
+       /* export the GPIO to userspace */
+       int gpio_export(unsigned gpio, bool direction_may_change);
+
+       /* reverse gpio_export() */
+       void gpio_unexport();
+
+After a kernel driver requests a GPIO, it may only be made available in
+the sysfs interface by gpio_export().  The driver can control whether the
+signal direction may change.  This helps drivers prevent userspace code
+from accidentally clobbering important system state.
+
+This explicit exporting can help with debugging (by making some kinds
+of experiments easier), or can provide an always-there interface that's
+suitable for documenting as part of a board support package.
--- a/arch/arm/plat-omap/gpio.c
+++ b/arch/arm/plat-omap/gpio.c
@@ -1488,6 +1488,9 @@ static int __init _omap_gpio_init(void)
                bank->chip.set = gpio_set;
                if (bank_is_mpuio(bank)) {
                        bank->chip.label = "mpuio";
+#ifdef CONFIG_ARCH_OMAP1
+                       bank->chip.dev = &omap_mpuio_device.dev;
+#endif
                        bank->chip.base = OMAP_MPUIO(0);
                } else {
                        bank->chip.label = "gpio";
--- a/arch/avr32/mach-at32ap/pio.c
+++ b/arch/avr32/mach-at32ap/pio.c
@@ -358,6 +358,8 @@ static int __init pio_probe(struct platf
        pio->chip.label = pio->name;
        pio->chip.base = pdev->id * 32;
        pio->chip.ngpio = 32;
+       pio->chip.dev = &pdev->dev;
+       pio->chip.owner = THIS_MODULE;
 
        pio->chip.direction_input = direction_input;
        pio->chip.get = gpio_get;
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -23,6 +23,21 @@ config DEBUG_GPIO
          slower.  The diagnostics help catch the type of setup errors
          that are most common when setting up new platforms or boards.
 
+config GPIO_SYSFS
+       bool "/sys/class/gpio/... (sysfs interface)"
+       depends on SYSFS && EXPERIMENTAL
+       help
+         Say Y here to add a sysfs interface for GPIOs.
+
+         This is mostly useful to work around omissions in a system's
+         kernel support.  Those are common in custom and semicustom
+         hardware assembled using standard kernels with a minimum of
+         custom patches.  In those cases, userspace code may import
+         a given GPIO from the kernel, if no kernel driver requested it.
+
+         Kernel drivers may also request that a particular GPIO be
+         exported to userspace; this can be useful when debugging.
+
 # put expanders in the right section, in alphabetical order
 
 comment "I2C GPIO expanders:"
--- 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 +156,486 @@ 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.subsys.kobj.ktype) {
+               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),
+                                       "gpio%d", gpio);
+               if (dev) {
+                       dev_set_drvdata(dev, desc);
+                       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, desc, match_export);
+               if (dev) {
+                       dev_set_drvdata(dev, NULL);
+                       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.subsys.kobj.ktype)
+               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),
+                               "gpiochip%d", chip->base);
+       if (dev) {
+               dev_set_drvdata(dev, chip);
+               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, chip, match_export);
+       if (dev) {
+               dev_set_drvdata(dev, NULL);
+               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 +645,11 @@ 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 +672,7 @@ 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 +687,23 @@ 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 +740,10 @@ int gpiochip_remove(struct gpio_chip *ch
        }
 
        spin_unlock_irqrestore(&gpio_lock, flags);
+
+       if (status == 0)
+               gpiochip_unexport(chip);
+
        return status;
 }
 EXPORT_SYMBOL_GPL(gpiochip_remove);
@@ -296,6 +801,8 @@ void gpio_free(unsigned gpio)
                return;
        }
 
+       gpio_unexport(gpio);
+
        spin_lock_irqsave(&gpio_lock, flags);
 
        desc = &gpio_desc[gpio];
@@ -534,10 +1041,6 @@ EXPORT_SYMBOL_GPL(gpio_set_value_canslee
 
 #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 +1117,28 @@ static int gpiolib_show(struct seq_file 
        /* 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);
--- a/drivers/gpio/mcp23s08.c
+++ b/drivers/gpio/mcp23s08.c
@@ -239,6 +239,7 @@ static int mcp23s08_probe(struct spi_dev
        mcp->chip.base = pdata->base;
        mcp->chip.ngpio = 8;
        mcp->chip.can_sleep = 1;
+       mcp->chip.dev = &spi->dev;
        mcp->chip.owner = THIS_MODULE;
 
        spi_set_drvdata(spi, mcp);
--- a/drivers/gpio/pca953x.c
+++ b/drivers/gpio/pca953x.c
@@ -188,6 +188,7 @@ static void pca953x_setup_gpio(struct pc
        gc->base = chip->gpio_start;
        gc->ngpio = gpios;
        gc->label = chip->client->name;
+       gc->dev = &chip->client->dev;
        gc->owner = THIS_MODULE;
 }
 
--- a/drivers/gpio/pcf857x.c
+++ b/drivers/gpio/pcf857x.c
@@ -175,6 +175,7 @@ static int pcf857x_probe(struct i2c_clie
 
        gpio->chip.base = pdata->gpio_base;
        gpio->chip.can_sleep = 1;
+       gpio->chip.dev = &client->dev;
        gpio->chip.owner = THIS_MODULE;
 
        /* NOTE:  the OnSemi jlc1562b is also largely compatible with
--- a/drivers/i2c/chips/tps65010.c
+++ b/drivers/i2c/chips/tps65010.c
@@ -636,6 +636,8 @@ static int tps65010_probe(struct i2c_cli
                tps->outmask = board->outmask;
 
                tps->chip.label = client->name;
+               tps->chip.dev = &client->dev;
+               tps->chip.owner = THIS_MODULE;
 
                tps->chip.set = tps65010_gpio_set;
                tps->chip.direction_output = tps65010_output;
--- a/drivers/mfd/htc-egpio.c
+++ b/drivers/mfd/htc-egpio.c
@@ -318,6 +318,8 @@ static int __init egpio_probe(struct pla
                ei->chip[i].dev = &(pdev->dev);
                chip = &(ei->chip[i].chip);
                chip->label           = "htc-egpio";
+               chip->dev             = &pdev->dev;
+               chip->owner           = THIS_MODULE;
                chip->get             = egpio_get;
                chip->set             = egpio_set;
                chip->direction_input = egpio_direction_input;
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -32,6 +32,8 @@ struct module;
 /**
  * struct gpio_chip - abstract a GPIO controller
  * @label: for diagnostics
+ * @dev: optional device providing the GPIOs
+ * @owner: helps prevent removal of modules exporting active GPIOs
  * @direction_input: configures signal "offset" as input, or returns error
  * @get: returns value for signal "offset"; for output signals this
  *     returns either the value actually sensed, or zero
@@ -59,6 +61,7 @@ struct module;
  */
 struct gpio_chip {
        char                    *label;
+       struct device           *dev;
        struct module           *owner;
 
        int                     (*direction_input)(struct gpio_chip *chip,
@@ -74,6 +77,7 @@ struct gpio_chip {
        int                     base;
        u16                     ngpio;
        unsigned                can_sleep:1;
+       unsigned                exported:1;
 };
 
 extern const char *gpiochip_is_requested(struct gpio_chip *chip,
@@ -108,7 +112,18 @@ extern void __gpio_set_value(unsigned gp
 extern int __gpio_cansleep(unsigned gpio);
 
 
-#else
+#ifdef CONFIG_GPIO_SYSFS
+
+/*
+ * A sysfs interface can be exported by individual drivers if they want,
+ * but more typically is configured entirely from userspace.
+ */
+extern int gpio_export(unsigned gpio, bool direction_may_change);
+extern void gpio_unexport(unsigned gpio);
+
+#endif /* CONFIG_GPIO_SYSFS */
+
+#else  /* !CONFIG_HAVE_GPIO_LIB */
 
 static inline int gpio_is_valid(int number)
 {
@@ -137,6 +152,22 @@ static inline void gpio_set_value_cansle
        gpio_set_value(gpio, value);
 }
 
-#endif
+#endif /* !CONFIG_HAVE_GPIO_LIB */
+
+#ifndef CONFIG_GPIO_SYSFS
+
+#include <asm/errno.h>
+
+/* sysfs support is only available with gpiolib, where it's optional */
+
+static inline int gpio_export(unsigned gpio, bool direction_may_change)
+{
+       return -ENOSYS;
+}
+
+static inline void gpio_unexport(unsigned gpio)
+{
+}
+#endif /* CONFIG_GPIO_SYSFS */
 
 #endif /* _ASM_GENERIC_GPIO_H */
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -79,6 +79,19 @@ static inline void gpio_set_value_cansle
        WARN_ON(1);
 }
 
+static inline int gpio_export(unsigned gpio, bool direction_may_change)
+{
+       /* GPIO can never have been requested or set as {in,out}put */
+       WARN_ON(1);
+       return -EINVAL;
+}
+
+static inline void gpio_unexport(unsigned gpio)
+{
+       /* GPIO can never have been exported */
+       WARN_ON(1);
+}
+
 static inline int gpio_to_irq(unsigned gpio)
 {
        /* GPIO can never have been requested or set as input */