diff options
Diffstat (limited to 'Documentation/admin-guide/gpio')
-rw-r--r-- | Documentation/admin-guide/gpio/gpio-mockup.rst | 8 | ||||
-rw-r--r-- | Documentation/admin-guide/gpio/index.rst | 6 | ||||
-rw-r--r-- | Documentation/admin-guide/gpio/obsolete.rst | 13 | ||||
-rw-r--r-- | Documentation/admin-guide/gpio/sysfs.rst | 167 |
4 files changed, 24 insertions, 170 deletions
diff --git a/Documentation/admin-guide/gpio/gpio-mockup.rst b/Documentation/admin-guide/gpio/gpio-mockup.rst index 493071da1738..d6e7438a7550 100644 --- a/Documentation/admin-guide/gpio/gpio-mockup.rst +++ b/Documentation/admin-guide/gpio/gpio-mockup.rst @@ -3,6 +3,14 @@ GPIO Testing Driver =================== +.. note:: + + This module has been obsoleted by the more flexible gpio-sim.rst. + New developments should use that API and existing developments are + encouraged to migrate as soon as possible. + This module will continue to be maintained but no new features will be + added. + The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO chips for testing purposes. The lines exposed by these chips can be accessed using the standard GPIO character device interface as well as manipulated diff --git a/Documentation/admin-guide/gpio/index.rst b/Documentation/admin-guide/gpio/index.rst index f6861ca16ffe..460afd29617e 100644 --- a/Documentation/admin-guide/gpio/index.rst +++ b/Documentation/admin-guide/gpio/index.rst @@ -1,16 +1,16 @@ .. SPDX-License-Identifier: GPL-2.0 ==== -gpio +GPIO ==== .. toctree:: :maxdepth: 1 + Character Device Userspace API <../../userspace-api/gpio/chardev> gpio-aggregator - sysfs - gpio-mockup gpio-sim + Obsolete APIs <obsolete> .. only:: subproject and html diff --git a/Documentation/admin-guide/gpio/obsolete.rst b/Documentation/admin-guide/gpio/obsolete.rst new file mode 100644 index 000000000000..5adbff02d61f --- /dev/null +++ b/Documentation/admin-guide/gpio/obsolete.rst @@ -0,0 +1,13 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================== +Obsolete GPIO APIs +================== + +.. toctree:: + :maxdepth: 1 + + Character Device Userspace API (v1) <../../userspace-api/gpio/chardev_v1> + Sysfs Interface <../../userspace-api/gpio/sysfs> + Mockup Testing Module <gpio-mockup> + diff --git a/Documentation/admin-guide/gpio/sysfs.rst b/Documentation/admin-guide/gpio/sysfs.rst deleted file mode 100644 index 35171d15f78d..000000000000 --- a/Documentation/admin-guide/gpio/sysfs.rst +++ /dev/null @@ -1,167 +0,0 @@ -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 gpiod_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. |