Kernel code may export it for complete or partial access.
GPIOs are identified as they are inside the kernel, using integers in
- the range 0..INT_MAX. See Documentation/gpio for more information.
+ the range 0..INT_MAX. See Documentation/admin-guide/gpio for more information.
/sys/class/gpio
/export ... asks the kernel to export a GPIO to userspace
--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0
+
+====
+gpio
+====
+
+.. toctree::
+ :maxdepth: 1
+
+ sysfs
+
+.. only:: subproject and html
+
+ Indices
+ =======
+
+ * :ref:`genindex`
--- /dev/null
+GPIO Sysfs Interface for Userspace
+==================================
+
+.. warning::
+
+ THIS ABI IS DEPRECATED, THE ABI DOCUMENTATION HAS BEEN MOVED TO
+ Documentation/ABI/obsolete/sysfs-gpio AND NEW USERSPACE CONSUMERS
+ ARE SUPPOSED TO USE THE CHARACTER DEVICE ABI. THIS OLD SYSFS ABI WILL
+ NOT BE DEVELOPED (NO NEW FEATURES), IT WILL JUST BE MAINTAINED.
+
+Refer to the examples in tools/gpio/* for an introduction to the new
+character device ABI. Also see the userspace header in
+include/uapi/linux/gpio.h
+
+The deprecated sysfs ABI
+------------------------
+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 appropriate 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.
+
+DO NOT ABUSE SYSFS TO CONTROL HARDWARE THAT HAS PROPER KERNEL DRIVERS.
+PLEASE READ THE DOCUMENT AT Documentation/driver-api/gpio/drivers-on-gpio.rst
+TO AVOID REINVENTING KERNEL WHEELS IN USERSPACE. I MEAN IT. REALLY.
+
+Paths in Sysfs
+--------------
+There are three kinds of entries 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.
+
+ If the pin can be configured as interrupt-generating interrupt
+ and if it has been configured to generate interrupts (see the
+ description of "edge"), you can poll(2) on that file and
+ poll(2) will return whenever the interrupt was triggered. If
+ you use poll(2), set the events POLLPRI and POLLERR. If you
+ use select(2), set the file descriptor in exceptfds. After
+ poll(2) returns, either lseek(2) to the beginning of the sysfs
+ file and read the new value or close the file and re-open it
+ to read the value.
+
+ "edge" ...
+ reads as either "none", "rising", "falling", or
+ "both". Write these strings to select the signal edge(s)
+ that will make poll(2) on the "value" file return.
+
+ This file exists only if the pin can be configured as an
+ interrupt generating input pin.
+
+ "active_low" ...
+ reads as either 0 (false) or 1 (true). Write
+ any nonzero value to invert the value attribute both
+ for reading and writing. Existing and subsequent
+ poll(2) support configuration via the edge attribute
+ for "rising" and "falling" edges will follow this
+ setting.
+
+GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (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 manages (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 gpiod_export(struct gpio_desc *desc, bool direction_may_change);
+
+ /* reverse gpio_export() */
+ void gpiod_unexport(struct gpio_desc *desc);
+
+ /* create a sysfs link to an exported GPIO node */
+ int gpiod_export_link(struct device *dev, const char *name,
+ struct gpio_desc *desc);
+
+After a kernel driver requests a GPIO, it may only be made available in
+the sysfs interface by gpiod_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.
+
+After the GPIO has been exported, gpiod_export_link() allows creating
+symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
+use this to provide the interface under their own device in sysfs with
+a descriptive name.
cputopology
device-mapper/index
efi-stub
+ gpio/index
highuid
hw_random
iostats
we need to translate them to the corresponding Linux GPIO descriptors.
There is a standard GPIO API for that and is documented in
-Documentation/gpio/.
+Documentation/admin-guide/gpio/.
In the above example we can get the corresponding two GPIO descriptors with
a code like this::
+++ /dev/null
-:orphan:
-
-====
-gpio
-====
-
-.. toctree::
- :maxdepth: 1
-
- sysfs
-
-.. only:: subproject and html
-
- Indices
- =======
-
- * :ref:`genindex`
+++ /dev/null
-GPIO Sysfs Interface for Userspace
-==================================
-
-.. warning::
-
- THIS ABI IS DEPRECATED, THE ABI DOCUMENTATION HAS BEEN MOVED TO
- Documentation/ABI/obsolete/sysfs-gpio AND NEW USERSPACE CONSUMERS
- ARE SUPPOSED TO USE THE CHARACTER DEVICE ABI. THIS OLD SYSFS ABI WILL
- NOT BE DEVELOPED (NO NEW FEATURES), IT WILL JUST BE MAINTAINED.
-
-Refer to the examples in tools/gpio/* for an introduction to the new
-character device ABI. Also see the userspace header in
-include/uapi/linux/gpio.h
-
-The deprecated sysfs ABI
-------------------------
-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 appropriate 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.
-
-DO NOT ABUSE SYSFS TO CONTROL HARDWARE THAT HAS PROPER KERNEL DRIVERS.
-PLEASE READ THE DOCUMENT AT Documentation/driver-api/gpio/drivers-on-gpio.rst
-TO AVOID REINVENTING KERNEL WHEELS IN USERSPACE. I MEAN IT. REALLY.
-
-Paths in Sysfs
---------------
-There are three kinds of entries 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.
-
- If the pin can be configured as interrupt-generating interrupt
- and if it has been configured to generate interrupts (see the
- description of "edge"), you can poll(2) on that file and
- poll(2) will return whenever the interrupt was triggered. If
- you use poll(2), set the events POLLPRI and POLLERR. If you
- use select(2), set the file descriptor in exceptfds. After
- poll(2) returns, either lseek(2) to the beginning of the sysfs
- file and read the new value or close the file and re-open it
- to read the value.
-
- "edge" ...
- reads as either "none", "rising", "falling", or
- "both". Write these strings to select the signal edge(s)
- that will make poll(2) on the "value" file return.
-
- This file exists only if the pin can be configured as an
- interrupt generating input pin.
-
- "active_low" ...
- reads as either 0 (false) or 1 (true). Write
- any nonzero value to invert the value attribute both
- for reading and writing. Existing and subsequent
- poll(2) support configuration via the edge attribute
- for "rising" and "falling" edges will follow this
- setting.
-
-GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (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 manages (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 gpiod_export(struct gpio_desc *desc, bool direction_may_change);
-
- /* reverse gpio_export() */
- void gpiod_unexport(struct gpio_desc *desc);
-
- /* create a sysfs link to an exported GPIO node */
- int gpiod_export_link(struct device *dev, const char *name,
- struct gpio_desc *desc);
-
-After a kernel driver requests a GPIO, it may only be made available in
-the sysfs interface by gpiod_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.
-
-After the GPIO has been exported, gpiod_export_link() allows creating
-symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
-use this to provide the interface under their own device in sysfs with
-a descriptive name.
-Chinese translated version of Documentation/gpio
+Chinese translated version of Documentation/admin-guide/gpio
If you have any comment or update to the content, please contact the
original document maintainer directly. However, if you have a problem
Linus Walleij <linus.walleij@linaro.org>
Chinese maintainer: Fu Wei <tekkamanninja@gmail.com>
---------------------------------------------------------------------
-Documentation/gpio 的中文翻译
+Documentation/admin-guide/gpio 的中文翻译
如果想评论或更新本文的内容，请直接联系原文档的维护者。如果你使用英文
交流有困难的话，也可以向中文版维护者求助。如果本翻译更新不及时或者翻
S: Maintained
F: Documentation/devicetree/bindings/gpio/
F: Documentation/driver-api/gpio/
-F: Documentation/gpio/
+F: Documentation/admin-guide/gpio/
F: Documentation/ABI/testing/gpio-cdev
F: Documentation/ABI/obsolete/sysfs-gpio
F: drivers/gpio/
projects / linux-2.6-microblaze.git / commitdiff