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
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.
#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.
#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;
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
* 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.
*/
base = gpiochip_find_base(chip->ngpio);
if (base < 0) {
status = base;
- goto fail_unlock;
+ goto unlock;
}
chip->base = base;
}
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)
}
spin_unlock_irqrestore(&gpio_lock, flags);
+
+ if (status == 0)
+ gpiochip_unexport(chip);
+
return status;
}
EXPORT_SYMBOL_GPL(gpiochip_remove);
return;
}
+ gpio_unexport(gpio);
+
spin_lock_irqsave(&gpio_lock, flags);
desc = &gpio_desc[gpio];
#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;
/* 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);
projects / linux-2.6 / commitdiff