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[60.241.235.125]) by smtp.gmail.com with ESMTPSA id 4-20020aa79204000000b006d999f4a3c0sm6538365pfo.152.2024.01.14.16.50.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Jan 2024 16:50:12 -0800 (PST) From: Kent Gibson To: linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org, linux-doc@vger.kernel.org, brgl@bgdev.pl, linus.walleij@linaro.org, andy@kernel.org, corbet@lwn.net Cc: Kent Gibson Subject: [PATCH v2 6/9] Documentation: gpio: add chardev v1 userspace API documentation Date: Mon, 15 Jan 2024 08:48:44 +0800 Message-Id: <20240115004847.22369-7-warthog618@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240115004847.22369-1-warthog618@gmail.com> References: <20240115004847.22369-1-warthog618@gmail.com> Precedence: bulk X-Mailing-List: linux-gpio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add documentation for v1 of the GPIO character device userspace API to the obsolete section of both the admin-guide and userspace-api books. Signed-off-by: Kent Gibson --- Documentation/admin-guide/gpio/obsolete.rst | 1 + .../userspace-api/gpio/chardev_v1.rst | 131 ++++++++++++++++++ .../gpio/gpio-get-lineevent-ioctl.rst | 78 +++++++++++ .../gpio/gpio-get-linehandle-ioctl.rst | 86 ++++++++++++ .../gpio/gpio-get-lineinfo-ioctl.rst | 54 ++++++++ .../gpio/gpio-get-lineinfo-unwatch-ioctl.rst | 2 +- .../gpio/gpio-get-lineinfo-watch-ioctl.rst | 74 ++++++++++ .../gpio-handle-get-line-values-ioctl.rst | 56 ++++++++ .../gpio/gpio-handle-set-config-ioctl.rst | 62 +++++++++ .../gpio-handle-set-line-values-ioctl.rst | 48 +++++++ .../gpio/gpio-lineevent-data-read.rst | 84 +++++++++++ .../gpio/gpio-lineinfo-changed-read.rst | 87 ++++++++++++ Documentation/userspace-api/gpio/obsolete.rst | 1 + 13 files changed, 763 insertions(+), 1 deletion(-) create mode 100644 Documentation/userspace-api/gpio/chardev_v1.rst create mode 100644 Documentation/userspace-api/gpio/gpio-get-lineevent-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-get-lineinfo-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-get-lineinfo-watch-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-handle-get-line-values-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-handle-set-config-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-handle-set-line-values-ioctl.rst create mode 100644 Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst create mode 100644 Documentation/userspace-api/gpio/gpio-lineinfo-changed-read.rst diff --git a/Documentation/admin-guide/gpio/obsolete.rst b/Documentation/admin-guide/gpio/obsolete.rst index dbf88f13c680..5926e5440207 100644 --- a/Documentation/admin-guide/gpio/obsolete.rst +++ b/Documentation/admin-guide/gpio/obsolete.rst @@ -7,5 +7,6 @@ Obsolete GPIO APIs .. toctree:: :maxdepth: 1 + Character Device Userspace API (v1) <../../userspace-api/gpio/chardev_v1> Sysfs Interface <../../userspace-api/gpio/sysfs> diff --git a/Documentation/userspace-api/gpio/chardev_v1.rst b/Documentation/userspace-api/gpio/chardev_v1.rst new file mode 100644 index 000000000000..67124b1d0487 --- /dev/null +++ b/Documentation/userspace-api/gpio/chardev_v1.rst @@ -0,0 +1,131 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================== +GPIO Character Device Userspace API (v1) +======================================== + +.. warning:: + This API is obsoleted by chardev.rst (v2). + + New developments should use the v2 API, and existing developments are + encouraged to migrate as soon as possible, as this API will be removed + in the future. The v2 API is a functional superset of the v1 API so any + v1 call can be directly translated to a v2 equivalent. + + This interface will continue to be maintained for the migration period, + but new features will only be added to the new API. + +First added in 4.8. + +The API is based around three major objects, the :ref:`gpio-v1-chip`, the +:ref:`gpio-v1-line-handle`, and the :ref:`gpio-v1-line-event`. + +Where "line event" is used in this document it refers to the request that can +monitor a line for edge events, not the edge events themselves. + +.. _gpio-v1-chip: + +Chip +==== + +The Chip represents a single GPIO chip and is exposed to userspace using device +files of the form ``/dev/gpiochipX``. + +Each chip supports a number of GPIO lines, +:c:type:`chip.lines`. Lines on the chip are identified by an +``offset`` in the range from 0 to ``chip.lines - 1``, i.e. `[0,chip.lines)`. + +Lines are requested from the chip using either gpio-get-linehandle-ioctl.rst +and the resulting line handle is used to access the GPIO chip's lines, or +gpio-get-lineevent-ioctl.rst and the resulting line event is used to monitor +a GPIO line for edge events. + +Within this documentation, the file descriptor returned by calling `open()` +on the GPIO device file is referred to as ``chip_fd``. + +Operations +---------- + +The following operations may be performed on the chip: + +.. toctree:: + :titlesonly: + + Get Line Handle + Get Line Event + Get Chip Info + Get Line Info + Watch Line Info + Unwatch Line Info + Read Line Info Changed Events + +.. _gpio-v1-line-handle: + +Line Handle +=========== + +Line handles are created by gpio-get-linehandle-ioctl.rst and provide +access to a set of requested lines. The line handle is exposed to userspace +via the anonymous file descriptor returned in +:c:type:`request.fd` by gpio-get-linehandle-ioctl.rst. + +Within this documentation, the line handle file descriptor is referred to +as ``handle_fd``. + +Operations +---------- + +The following operations may be performed on the line handle: + +.. toctree:: + :titlesonly: + + Get Line Values + Set Line Values + Reconfigure Lines + +.. _gpio-v1-line-event: + +Line Event +========== + +Line events are created by gpio-get-lineevent-ioctl.rst and provide +access to a requested line. The line event is exposed to userspace +via the anonymous file descriptor returned in +:c:type:`request.fd` by gpio-get-lineevent-ioctl.rst. + +Within this documentation, the line event file descriptor is referred to +as ``event_fd``. + +Operations +---------- + +The following operations may be performed on the line event: + +.. toctree:: + :titlesonly: + + Get Line Value + Read Line Edge Events + +Types +===== + +This section contains the structs that are referenced by the ABI v1. + +The :c:type:`struct gpiochip_info` is common to ABI v1 and v2. + +.. kernel-doc:: include/uapi/linux/gpio.h + :identifiers: + gpioevent_data + gpioevent_request + gpiohandle_config + gpiohandle_data + gpiohandle_request + gpioline_info + gpioline_info_changed + +.. toctree:: + :hidden: + + error-codes diff --git a/Documentation/userspace-api/gpio/gpio-get-lineevent-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-lineevent-ioctl.rst new file mode 100644 index 000000000000..7d0b932925c6 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-get-lineevent-ioctl.rst @@ -0,0 +1,78 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_GET_LINEEVENT_IOCTL: + +************************ +GPIO_GET_LINEEVENT_IOCTL +************************ + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-get-line-ioctl.rst. + +Name +==== + +GPIO_GET_LINEEVENT_IOCTL - Request a line with edge detection from the kernel. + +Synopsis +======== + +.. c:macro:: GPIO_GET_LINEEVENT_IOCTL + +``int ioctl(int chip_fd, GPIO_GET_LINEEVENT_IOCTL, struct gpioevent_request *request)`` + +Arguments +========= + +``chip_fd`` + The file descriptor of the GPIO character device returned by `open()`. + +``request`` + The :c:type:`event_request` specifying the line + to request and its configuration. + +Description +=========== + +Request a line with edge detection from the kernel. + +On success, the requesting process is granted exclusive access to the line +value and may receive events when edges are detected on the line, as +described in gpio-lineevent-data-read.rst. + +The state of a line is guaranteed to remain as requested until the returned +file descriptor is closed. Once the file descriptor is closed, the state of +the line becomes uncontrolled from the userspace perspective, and may revert +to its default state. + +Requesting a line already in use is an error (**EBUSY**). + +Closing the ``chip_fd`` has no effect on existing line events. + +Configuration Rules +------------------- + +The following configuration rules apply: + +The line event is requested as an input, so no flags specific to output lines, +``GPIOHANDLE_REQUEST_OUTPUT``, ``GPIOHANDLE_REQUEST_OPEN_DRAIN``, or +``GPIOHANDLE_REQUEST_OPEN_SOURCE``, may be set. + +Only one bias flag, ``GPIOHANDLE_REQUEST_BIAS_xxx``, may be set. +If no bias flags are set then the bias configuration is not changed. + +The edge flags, ``GPIOEVENT_REQUEST_RISING_EDGE`` and +``GPIOEVENT_REQUEST_FALLING_EDGE``, may be combined to detect both rising +and falling edges. + +Requesting an invalid configuration is an error (**EINVAL**). + +Return Value +============ + +On success 0 and the :c:type:`request.fd` contains the file +descriptor for the request. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst new file mode 100644 index 000000000000..c8256afe306e --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst @@ -0,0 +1,86 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_GET_LINEHANDLE_IOCTL: + +************************* +GPIO_GET_LINEHANDLE_IOCTL +************************* + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-get-line-ioctl.rst. + +Name +==== + +GPIO_GET_LINEHANDLE_IOCTL - Request a line or lines from the kernel. + +Synopsis +======== + +.. c:macro:: GPIO_GET_LINEHANDLE_IOCTL + +``int ioctl(int chip_fd, GPIO_GET_LINEHANDLE_IOCTL, struct gpiohandle_request *request)`` + +Arguments +========= + +``chip_fd`` + The file descriptor of the GPIO character device returned by `open()`. + +``request`` + The :c:type:`handle_request` specifying the lines to + request and their configuration. + +Description +=========== + +Request a line or lines from the kernel. + +While multiple lines may be requested, the same configuration applies to all +lines in the request. + +On success, the requesting process is granted exclusive access to the line +value and write access to the line configuration. + +The state of a line, including the value of output lines, is guaranteed to +remain as requested until the returned file descriptor is closed. Once the +file descriptor is closed, the state of the line becomes uncontrolled from +the userspace perspective, and may revert to its default state. + +Requesting a line already in use is an error (**EBUSY**). + +Closing the ``chip_fd`` has no effect on existing line handles. + +.. _gpio-get-linehandle-config-rules: + +Configuration Rules +------------------- + +The following configuration rules apply: + +The direction flags, ``GPIOHANDLE_REQUEST_INPUT`` and +``GPIOHANDLE_REQUEST_OUTPUT``, cannot be combined. If neither are set then the +only other flag that may be set is ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` and the +line is requested "as-is" to allow reading of the line value without altering +the electrical configuration. + +The drive flags, ``GPIOHANDLE_REQUEST_OPEN_xxx``, require the +``GPIOHANDLE_REQUEST_OUTPUT`` to be set. +Only one drive flag may be set. +If none are set then the line is assumed push-pull. + +Only one bias flag, ``GPIOHANDLE_REQUEST_BIAS_xxx``, may be set, and +it requires a direction flag to also be set. +If no bias flags are set then the bias configuration is not changed. + +Requesting an invalid configuration is an error (**EINVAL**). + +Return Value +============ + +On success 0 and the :c:type:`request.fd` contains the +file descriptor for the request. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-get-lineinfo-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-lineinfo-ioctl.rst new file mode 100644 index 000000000000..c895b8910b25 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-get-lineinfo-ioctl.rst @@ -0,0 +1,54 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_GET_LINEINFO_IOCTL: + +*********************** +GPIO_GET_LINEINFO_IOCTL +*********************** + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-get-lineinfo-ioctl.rst. + +Name +==== + +GPIO_GET_LINEINFO_IOCTL - Get the publicly available information for a line. + +Synopsis +======== + +.. c:macro:: GPIO_GET_LINEINFO_IOCTL + +``int ioctl(int chip_fd, GPIO_GET_LINEINFO_IOCTL, struct gpioline_info *info)`` + +Arguments +========= + +``chip_fd`` + The file descriptor of the GPIO character device returned by `open()`. + +``info`` + The :c:type:`line_info` to be populated, with the + ``offset`` field set to indicate the line to be collected. + +Description +=========== + +Get the publicly available information for a line. + +This information is available independent of whether the line is in use. + +.. note:: + The line info does not include the line value. + + The line must be requested using gpio-get-linehandle-ioctl.rst or + gpio-get-lineevent-ioctl.rst to access its value. + +Return Value +============ + +On success 0 and ``info`` is populated with the chip info. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-get-lineinfo-unwatch-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-lineinfo-unwatch-ioctl.rst index 2fec6f12e3bf..a82d0161daf8 100644 --- a/Documentation/userspace-api/gpio/gpio-get-lineinfo-unwatch-ioctl.rst +++ b/Documentation/userspace-api/gpio/gpio-get-lineinfo-unwatch-ioctl.rst @@ -33,7 +33,7 @@ Description Remove the line from the list of lines being watched on this ``chip_fd``. -This is the opposite of gpio-v2-get-lineinfo-watch-ioctl.rst (v2) and +This is the reverse of gpio-v2-get-lineinfo-watch-ioctl.rst (v2) and gpio-get-lineinfo-watch-ioctl.rst (v1). Unwatching a line that is not watched is an error (**EBUSY**). diff --git a/Documentation/userspace-api/gpio/gpio-get-lineinfo-watch-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-lineinfo-watch-ioctl.rst new file mode 100644 index 000000000000..f5c92b69a496 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-get-lineinfo-watch-ioctl.rst @@ -0,0 +1,74 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_GET_LINEINFO_WATCH_IOCTL: + +***************************** +GPIO_GET_LINEINFO_WATCH_IOCTL +***************************** + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-get-lineinfo-watch-ioctl.rst. + +Name +==== + +GPIO_GET_LINEINFO_WATCH_IOCTL - Enable watching a line for changes to its +request state and configuration information. + +Synopsis +======== + +.. c:macro:: GPIO_GET_LINEINFO_WATCH_IOCTL + +``int ioctl(int chip_fd, GPIO_GET_LINEINFO_WATCH_IOCTL, struct gpioline_info *info)`` + +Arguments +========= + +``chip_fd`` + The file descriptor of the GPIO character device returned by `open()`. + +``info`` + The :c:type:`line_info` struct to be populated, with + the ``offset`` set to indicate the line to watch + +Description +=========== + +Enable watching a line for changes to its request state and configuration +information. Changes to line info include a line being requested, released +or reconfigured. + +.. note:: + Watching line info is not generally required, and would typically only be + used by a system monitoring component. + + The line info does NOT include the line value. + + The line must be requested using gpio-get-linehandle-ioctl.rst or + gpio-get-lineevent-ioctl.rst to access its value, and the line event can + monitor a line for events using gpio-lineevent-data-read.rst. + +By default all lines are unwatched when the GPIO chip is opened. + +Multiple lines may be watched simultaneously by adding a watch for each. + +Once a watch is set, any changes to line info will generate events which can be +read from the ``chip_fd`` as described in +gpio-lineinfo-changed-read.rst. + +Adding a watch to a line that is already watched is an error (**EBUSY**). + +Watches are specific to the ``chip_fd`` and are independent of watches +on the same GPIO chip opened with a separate call to `open()`. + +First added in 5.7. + +Return Value +============ + +On success 0 and ``info`` is populated with the current line info. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-handle-get-line-values-ioctl.rst b/Documentation/userspace-api/gpio/gpio-handle-get-line-values-ioctl.rst new file mode 100644 index 000000000000..25263b8f0588 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-handle-get-line-values-ioctl.rst @@ -0,0 +1,56 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIOHANDLE_GET_LINE_VALUES_IOCTL: + +******************************** +GPIOHANDLE_GET_LINE_VALUES_IOCTL +******************************** +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-line-get-values-ioctl.rst. + +Name +==== + +GPIOHANDLE_GET_LINE_VALUES_IOCTL - Get the values of all requested lines. + +Synopsis +======== + +.. c:macro:: GPIOHANDLE_GET_LINE_VALUES_IOCTL + +``int ioctl(int handle_fd, GPIOHANDLE_GET_LINE_VALUES_IOCTL, struct gpiohandle_data *values)`` + +Arguments +========= + +``handle_fd`` + The file descriptor of the GPIO character device, as returned in the + :c:type:`request.fd` by gpio-get-linehandle-ioctl.rst. + +``values`` + The :c:type:`line_values` to be populated. + +Description +=========== + +Get the values of all requested lines. + +The values of both input and output lines may be read. + +For output lines, the value returned is driver and configuration dependent and +may be either the output buffer (the last requested value set) or the input +buffer (the actual level of the line), and depending on the hardware and +configuration these may differ. + +This ioctl can also be used to read the line value for line events, +substituting the ``event_fd`` for the ``handle_fd``. As there is only +one line requested in that case, only the one value is returned in ``values``. + +Return Value +============ + +On success 0 and ``values`` populated with the values read. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-handle-set-config-ioctl.rst b/Documentation/userspace-api/gpio/gpio-handle-set-config-ioctl.rst new file mode 100644 index 000000000000..8f1e748dccc8 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-handle-set-config-ioctl.rst @@ -0,0 +1,62 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIOHANDLE_SET_CONFIG_IOCTL: + +*************************** +GPIOHANDLE_SET_CONFIG_IOCTL +*************************** + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-line-set-config-ioctl.rst. + +Name +==== + +GPIOHANDLE_SET_CONFIG_IOCTL - Update the configuration of previously requested lines. + +Synopsis +======== + +.. c:macro:: GPIOHANDLE_SET_CONFIG_IOCTL + +``int ioctl(int handle_fd, GPIOHANDLE_SET_CONFIG_IOCTL, struct gpiohandle_config *config)`` + +Arguments +========= + +``handle_fd`` + The file descriptor of the GPIO character device, as returned in the + :c:type:`request.fd` by gpio-get-linehandle-ioctl.rst. + +``config`` + The new :c:type:`configuration` to apply to the + requested lines. + +Description +=========== + +Update the configuration of previously requested lines, without releasing the +line or introducing potential glitches. + +The configuration applies to all requested lines. + +The same :ref:`gpio-get-linehandle-config-rules` that apply when requesting the +lines also apply when updating the line configuration. + +The motivating use case for this command is changing direction of +bi-directional lines between input and output, but it may be used more +generally move lines seamlessly from one configuration state to another. + +To only change the value of output lines, use +gpio-handle-set-line-values-ioctl.rst. + +First added in 5.5. + +Return Value +============ + +On success 0. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-handle-set-line-values-ioctl.rst b/Documentation/userspace-api/gpio/gpio-handle-set-line-values-ioctl.rst new file mode 100644 index 000000000000..0aa05e623a6c --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-handle-set-line-values-ioctl.rst @@ -0,0 +1,48 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_HANDLE_SET_LINE_VALUES_IOCTL: + +********************************* +GPIO_HANDLE_SET_LINE_VALUES_IOCTL +********************************* +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-line-set-values-ioctl.rst. + +Name +==== + +GPIO_HANDLE_SET_LINE_VALUES_IOCTL - Set the values of all requested output lines. + +Synopsis +======== + +.. c:macro:: GPIO_HANDLE_SET_LINE_VALUES_IOCTL + +``int ioctl(int handle_fd, GPIO_HANDLE_SET_LINE_VALUES_IOCTL, struct gpiohandle_data *values)`` + +Arguments +========= + +``handle_fd`` + The file descriptor of the GPIO character device, as returned in the + :c:type:`request.fd` by gpio-get-linehandle-ioctl.rst. + +``values`` + The :c:type:`line_values` to set. + +Description +=========== + +Set the values of all requested output lines. + +Only the values of output lines may be set. +Attempting to set the value of input lines is an error (**EPERM**). + +Return Value +============ + +On success 0. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst b/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst new file mode 100644 index 000000000000..68b8d4f9f604 --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst @@ -0,0 +1,84 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_LINEEVENT_DATA_READ: + +************************ +GPIO_LINEEVENT_DATA_READ +************************ + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-line-event-read.rst. + +Name +==== + +GPIO_LINEEVENT_DATA_READ - Read edge detection events from a line event. + +Synopsis +======== + +``int read(int event_fd, void *buf, size_t count)`` + +Arguments +========= + +``event_fd`` + The file descriptor of the GPIO character device, as returned in the + :c:type:`request.fd` by gpio-get-lineevent-ioctl.rst. + +``buf`` + The buffer to contain the :c:type:`events`. + +``count`` + The number of bytes available in ``buf``, which must be at + least the size of a :c:type:`gpioevent_data`. + +Description +=========== + +Read edge detection events for a line from a line event. + +Edge detection must be enabled for the input line using either +``GPIOEVENT_REQUEST_RISING_EDGE`` or ``GPIOEVENT_REQUEST_FALLING_EDGE``, or +both. Edge events are then generated whenever edge interrupts are detected on +the input line. + +The kernel captures and timestamps edge events as close as possible to their +occurrence and stores them in a buffer from where they can be read by +userspace at its convenience using `read()`. + +The source of the clock for :c:type:`event.timestamp` is +``CLOCK_MONOTONIC``, except for kernels earlier than Linux 5.7 when it was +``CLOCK_REALTIME``. There is no indication in the :c:type:`gpioevent_data` +as to which clock source is used, it must be determined from either the kernel +version or sanity checks on the timestamp itself. + +Events read from the buffer are always in the same order that they were +detected by the kernel. + +The size of the kernel event buffer is fixed at 16 events. + +The buffer may overflow if bursts of events occur quicker than they are read +by userspace. If an overflow occurs then the most recent event is discarded. +Overflow cannot be detected from userspace. + +To minimize the number of calls required to copy events from the kernel to +userspace, `read()` supports copying multiple events. The number of events +copied is the lower of the number available in the kernel buffer and the +number that will fit in the userspace buffer (``buf``). + +The `read()` will block if no event is available and the ``event_fd`` has not +been set **O_NONBLOCK**. + +The presence of an event can be tested for by checking that the ``event_fd`` is +readable using `poll()` or an equivalent. + +Return Value +============ + +On success the number of bytes read, which will be a multiple of the size of +a :c:type:`gpio_lineevent_data` event. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/gpio-lineinfo-changed-read.rst b/Documentation/userspace-api/gpio/gpio-lineinfo-changed-read.rst new file mode 100644 index 000000000000..c4f5e1787a9d --- /dev/null +++ b/Documentation/userspace-api/gpio/gpio-lineinfo-changed-read.rst @@ -0,0 +1,87 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _GPIO_LINEINFO_CHANGED_READ: + +************************** +GPIO_LINEINFO_CHANGED_READ +************************** + +.. warning:: + This ioctl is part of chardev_v1.rst and is obsoleted by + gpio-v2-lineinfo-changed-read.rst. + +Name +==== + +GPIO_LINEINFO_CHANGED_READ - Read line info change events for watched lines +from the chip. + +Synopsis +======== + +``int read(int chip_fd, void *buf, size_t count)`` + +Arguments +========= + +``chip_fd`` + The file descriptor of the GPIO character device returned by `open()`. + +``buf`` + The buffer to contain the :c:type:`events`. + +``count`` + The number of bytes available in ``buf``, which must be at least the size + of a :c:type:`gpioline_info_changed` event. + +Description +=========== + +Read line info change events for watched lines from the chip. + +.. note:: + Monitoring line info changes is not generally required, and would typically + only be performed by a system monitoring component. + + These events relate to changes in a line's request state or configuration, + not its value. Use gpio-lineevent-data-read.rst to receive events when a + line changes value. + +A line must be watched using gpio-get-lineinfo-watch-ioctl.rst to generate +info changed events. Subsequently, a request, release, or reconfiguration +of the line will generate an info changed event. + +The kernel timestamps events when they occur and stores them in a buffer +from where they can be read by userspace at its convenience using `read()`. + +The size of the kernel event buffer is fixed at 32 events per ``chip_fd``. + +The buffer may overflow if bursts of events occur quicker than they are read +by userspace. If an overflow occurs then the most recent event is discarded. +Overflow cannot be detected from userspace. + +Events read from the buffer are always in the same order that they were +detected by the kernel, including when multiple lines are being monitored by +the one ``chip_fd``. + +To minimize the number of calls required to copy events from the kernel to +userspace, `read()` supports copying multiple events. The number of events +copied is the lower of the number available in the kernel buffer and the +number that will fit in the userspace buffer (``buf``). + +A `read()` will block if no event is available and the ``chip_fd`` has not +been set **O_NONBLOCK**. + +The presence of an event can be tested for by checking that the ``chip_fd`` is +readable using `poll()` or an equivalent. + +First added in 5.7. + +Return Value +============ + +On success the number of bytes read, which will be a multiple of the size of +a :c:type:`gpioline_info_changed` event. + +On error -1 and the ``errno`` variable is set appropriately. +Common error codes are described in error-codes.rst. diff --git a/Documentation/userspace-api/gpio/obsolete.rst b/Documentation/userspace-api/gpio/obsolete.rst index c27bd6014a3d..c42538b44ec8 100644 --- a/Documentation/userspace-api/gpio/obsolete.rst +++ b/Documentation/userspace-api/gpio/obsolete.rst @@ -7,4 +7,5 @@ Obsolete GPIO Userspace APIs .. toctree:: :maxdepth: 1 + Character Device Userspace API (v1) Sysfs Interface