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>
This commit is contained in:
David Brownell
committed by
Linus Torvalds
Linus Torvalds
parent
8b6dd98682
commit
d8f388d8dc
@ -23,6 +23,21 @@ config DEBUG_GPIO
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slower. The diagnostics help catch the type of setup errors
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that are most common when setting up new platforms or boards.
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config GPIO_SYSFS
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bool "/sys/class/gpio/... (sysfs interface)"
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depends on SYSFS && EXPERIMENTAL
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help
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Say Y here to add a sysfs interface for GPIOs.
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This is mostly useful to work around omissions in a system's
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kernel support. Those are common in custom and semicustom
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hardware assembled using standard kernels with a minimum of
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custom patches. In those cases, userspace code may import
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a given GPIO from the kernel, if no kernel driver requested it.
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Kernel drivers may also request that a particular GPIO be
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exported to userspace; this can be useful when debugging.
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# put expanders in the right section, in alphabetical order
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comment "I2C GPIO expanders:"
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@ -2,8 +2,11 @@
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#include <linux/module.h>
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#include <linux/irq.h>
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#include <linux/spinlock.h>
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#include <asm/gpio.h>
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#include <linux/device.h>
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#include <linux/err.h>
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#include <linux/debugfs.h>
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#include <linux/seq_file.h>
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#include <linux/gpio.h>
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/* Optional implementation infrastructure for GPIO interfaces.
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@ -44,6 +47,8 @@ struct gpio_desc {
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#define FLAG_REQUESTED 0
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#define FLAG_IS_OUT 1
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#define FLAG_RESERVED 2
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#define FLAG_EXPORT 3 /* protected by sysfs_lock */
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#define FLAG_SYSFS 4 /* exported via /sys/class/gpio/control */
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#ifdef CONFIG_DEBUG_FS
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const char *label;
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@ -151,6 +156,482 @@ err:
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return ret;
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}
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#ifdef CONFIG_GPIO_SYSFS
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/* lock protects against unexport_gpio() being called while
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* sysfs files are active.
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*/
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static DEFINE_MUTEX(sysfs_lock);
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/*
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* /sys/class/gpio/gpioN... only for GPIOs that are exported
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* /direction
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* * MAY BE OMITTED if kernel won't allow direction changes
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* * is read/write as "in" or "out"
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* * may also be written as "high" or "low", initializing
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* output value as specified ("out" implies "low")
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* /value
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* * always readable, subject to hardware behavior
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* * may be writable, as zero/nonzero
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*
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* REVISIT there will likely be an attribute for configuring async
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* notifications, e.g. to specify polling interval or IRQ trigger type
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* that would for example trigger a poll() on the "value".
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*/
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static ssize_t gpio_direction_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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const struct gpio_desc *desc = dev_get_drvdata(dev);
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ssize_t status;
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mutex_lock(&sysfs_lock);
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if (!test_bit(FLAG_EXPORT, &desc->flags))
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status = -EIO;
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else
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status = sprintf(buf, "%s\n",
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test_bit(FLAG_IS_OUT, &desc->flags)
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? "out" : "in");
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mutex_unlock(&sysfs_lock);
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return status;
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}
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static ssize_t gpio_direction_store(struct device *dev,
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struct device_attribute *attr, const char *buf, size_t size)
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{
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const struct gpio_desc *desc = dev_get_drvdata(dev);
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unsigned gpio = desc - gpio_desc;
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ssize_t status;
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mutex_lock(&sysfs_lock);
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if (!test_bit(FLAG_EXPORT, &desc->flags))
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status = -EIO;
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else if (sysfs_streq(buf, "high"))
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status = gpio_direction_output(gpio, 1);
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else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
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status = gpio_direction_output(gpio, 0);
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else if (sysfs_streq(buf, "in"))
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status = gpio_direction_input(gpio);
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else
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status = -EINVAL;
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mutex_unlock(&sysfs_lock);
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return status ? : size;
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}
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static const DEVICE_ATTR(direction, 0644,
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gpio_direction_show, gpio_direction_store);
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static ssize_t gpio_value_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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const struct gpio_desc *desc = dev_get_drvdata(dev);
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unsigned gpio = desc - gpio_desc;
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ssize_t status;
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mutex_lock(&sysfs_lock);
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if (!test_bit(FLAG_EXPORT, &desc->flags))
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status = -EIO;
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else
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status = sprintf(buf, "%d\n", gpio_get_value_cansleep(gpio));
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mutex_unlock(&sysfs_lock);
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return status;
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}
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static ssize_t gpio_value_store(struct device *dev,
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struct device_attribute *attr, const char *buf, size_t size)
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{
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const struct gpio_desc *desc = dev_get_drvdata(dev);
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unsigned gpio = desc - gpio_desc;
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ssize_t status;
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mutex_lock(&sysfs_lock);
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if (!test_bit(FLAG_EXPORT, &desc->flags))
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status = -EIO;
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else if (!test_bit(FLAG_IS_OUT, &desc->flags))
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status = -EPERM;
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else {
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long value;
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status = strict_strtol(buf, 0, &value);
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if (status == 0) {
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gpio_set_value_cansleep(gpio, value != 0);
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status = size;
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}
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}
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mutex_unlock(&sysfs_lock);
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return status;
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}
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static /*const*/ DEVICE_ATTR(value, 0644,
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gpio_value_show, gpio_value_store);
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static const struct attribute *gpio_attrs[] = {
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&dev_attr_direction.attr,
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&dev_attr_value.attr,
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NULL,
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};
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static const struct attribute_group gpio_attr_group = {
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.attrs = (struct attribute **) gpio_attrs,
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};
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/*
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* /sys/class/gpio/gpiochipN/
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* /base ... matching gpio_chip.base (N)
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* /label ... matching gpio_chip.label
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* /ngpio ... matching gpio_chip.ngpio
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*/
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static ssize_t chip_base_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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const struct gpio_chip *chip = dev_get_drvdata(dev);
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return sprintf(buf, "%d\n", chip->base);
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}
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static DEVICE_ATTR(base, 0444, chip_base_show, NULL);
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static ssize_t chip_label_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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const struct gpio_chip *chip = dev_get_drvdata(dev);
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return sprintf(buf, "%s\n", chip->label ? : "");
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}
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static DEVICE_ATTR(label, 0444, chip_label_show, NULL);
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static ssize_t chip_ngpio_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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const struct gpio_chip *chip = dev_get_drvdata(dev);
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return sprintf(buf, "%u\n", chip->ngpio);
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}
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static DEVICE_ATTR(ngpio, 0444, chip_ngpio_show, NULL);
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static const struct attribute *gpiochip_attrs[] = {
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&dev_attr_base.attr,
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&dev_attr_label.attr,
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&dev_attr_ngpio.attr,
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NULL,
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};
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static const struct attribute_group gpiochip_attr_group = {
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.attrs = (struct attribute **) gpiochip_attrs,
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};
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/*
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* /sys/class/gpio/export ... write-only
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* integer N ... number of GPIO to export (full access)
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* /sys/class/gpio/unexport ... write-only
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* integer N ... number of GPIO to unexport
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*/
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static ssize_t export_store(struct class *class, const char *buf, size_t len)
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{
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long gpio;
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int status;
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status = strict_strtol(buf, 0, &gpio);
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if (status < 0)
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goto done;
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/* No extra locking here; FLAG_SYSFS just signifies that the
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* request and export were done by on behalf of userspace, so
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* they may be undone on its behalf too.
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*/
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status = gpio_request(gpio, "sysfs");
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if (status < 0)
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goto done;
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status = gpio_export(gpio, true);
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if (status < 0)
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gpio_free(gpio);
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else
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set_bit(FLAG_SYSFS, &gpio_desc[gpio].flags);
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done:
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if (status)
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pr_debug("%s: status %d\n", __func__, status);
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return status ? : len;
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}
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static ssize_t unexport_store(struct class *class, const char *buf, size_t len)
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{
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long gpio;
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int status;
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status = strict_strtol(buf, 0, &gpio);
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if (status < 0)
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goto done;
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status = -EINVAL;
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/* reject bogus commands (gpio_unexport ignores them) */
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if (!gpio_is_valid(gpio))
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goto done;
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/* No extra locking here; FLAG_SYSFS just signifies that the
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* request and export were done by on behalf of userspace, so
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* they may be undone on its behalf too.
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*/
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if (test_and_clear_bit(FLAG_SYSFS, &gpio_desc[gpio].flags)) {
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status = 0;
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gpio_free(gpio);
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}
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done:
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if (status)
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pr_debug("%s: status %d\n", __func__, status);
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return status ? : len;
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}
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static struct class_attribute gpio_class_attrs[] = {
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__ATTR(export, 0200, NULL, export_store),
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__ATTR(unexport, 0200, NULL, unexport_store),
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__ATTR_NULL,
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};
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static struct class gpio_class = {
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.name = "gpio",
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.owner = THIS_MODULE,
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.class_attrs = gpio_class_attrs,
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};
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/**
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* gpio_export - export a GPIO through sysfs
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* @gpio: gpio to make available, already requested
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* @direction_may_change: true if userspace may change gpio direction
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* Context: arch_initcall or later
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*
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* When drivers want to make a GPIO accessible to userspace after they
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* have requested it -- perhaps while debugging, or as part of their
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* public interface -- they may use this routine. If the GPIO can
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* change direction (some can't) and the caller allows it, userspace
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* will see "direction" sysfs attribute which may be used to change
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* the gpio's direction. A "value" attribute will always be provided.
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*
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* Returns zero on success, else an error.
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*/
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int gpio_export(unsigned gpio, bool direction_may_change)
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{
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unsigned long flags;
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struct gpio_desc *desc;
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int status = -EINVAL;
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/* can't export until sysfs is available ... */
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if (!gpio_class.p) {
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pr_debug("%s: called too early!\n", __func__);
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return -ENOENT;
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}
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if (!gpio_is_valid(gpio))
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goto done;
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mutex_lock(&sysfs_lock);
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spin_lock_irqsave(&gpio_lock, flags);
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desc = &gpio_desc[gpio];
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if (test_bit(FLAG_REQUESTED, &desc->flags)
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&& !test_bit(FLAG_EXPORT, &desc->flags)) {
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status = 0;
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if (!desc->chip->direction_input
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|| !desc->chip->direction_output)
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direction_may_change = false;
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}
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spin_unlock_irqrestore(&gpio_lock, flags);
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if (status == 0) {
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struct device *dev;
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dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
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desc, "gpio%d", gpio);
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if (dev) {
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if (direction_may_change)
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status = sysfs_create_group(&dev->kobj,
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&gpio_attr_group);
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else
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status = device_create_file(dev,
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&dev_attr_value);
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if (status != 0)
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device_unregister(dev);
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} else
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status = -ENODEV;
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if (status == 0)
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set_bit(FLAG_EXPORT, &desc->flags);
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}
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mutex_unlock(&sysfs_lock);
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done:
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if (status)
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pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
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return status;
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}
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EXPORT_SYMBOL_GPL(gpio_export);
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static int match_export(struct device *dev, void *data)
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{
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return dev_get_drvdata(dev) == data;
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}
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/**
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* gpio_unexport - reverse effect of gpio_export()
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* @gpio: gpio to make unavailable
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*
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* This is implicit on gpio_free().
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*/
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void gpio_unexport(unsigned gpio)
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{
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struct gpio_desc *desc;
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int status = -EINVAL;
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|
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if (!gpio_is_valid(gpio))
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goto done;
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mutex_lock(&sysfs_lock);
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desc = &gpio_desc[gpio];
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if (test_bit(FLAG_EXPORT, &desc->flags)) {
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struct device *dev = NULL;
|
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dev = class_find_device(&gpio_class, NULL, desc, match_export);
|
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if (dev) {
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clear_bit(FLAG_EXPORT, &desc->flags);
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put_device(dev);
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device_unregister(dev);
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status = 0;
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} else
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status = -ENODEV;
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}
|
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|
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mutex_unlock(&sysfs_lock);
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done:
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if (status)
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pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
|
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}
|
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EXPORT_SYMBOL_GPL(gpio_unexport);
|
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|
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static int gpiochip_export(struct gpio_chip *chip)
|
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{
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int status;
|
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struct device *dev;
|
||||
|
||||
/* Many systems register gpio chips for SOC support very early,
|
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* before driver model support is available. In those cases we
|
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* 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);
|
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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);
|
||||
|
||||
@ -239,6 +239,7 @@ static int mcp23s08_probe(struct spi_device *spi)
|
||||
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);
|
||||
|
||||
@ -188,6 +188,7 @@ static void pca953x_setup_gpio(struct pca953x_chip *chip, int gpios)
|
||||
gc->base = chip->gpio_start;
|
||||
gc->ngpio = gpios;
|
||||
gc->label = chip->client->name;
|
||||
gc->dev = &chip->client->dev;
|
||||
gc->owner = THIS_MODULE;
|
||||
}
|
||||
|
||||
|
||||
@ -200,6 +200,7 @@ static int pcf857x_probe(struct i2c_client *client,
|
||||
|
||||
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
|
||||
|
||||
Reference in New Issue
Block a user