153 lines · plain
1.. SPDX-License-Identifier: GPL-2.02 3.. _GPIO_V2_GET_LINE_IOCTL:4 5**********************6GPIO_V2_GET_LINE_IOCTL7**********************8 9Name10====11 12GPIO_V2_GET_LINE_IOCTL - Request a line or lines from the kernel.13 14Synopsis15========16 17.. c:macro:: GPIO_V2_GET_LINE_IOCTL18 19``int ioctl(int chip_fd, GPIO_V2_GET_LINE_IOCTL, struct gpio_v2_line_request *request)``20 21Arguments22=========23 24``chip_fd``25 The file descriptor of the GPIO character device returned by `open()`.26 27``request``28 The :c:type:`line_request<gpio_v2_line_request>` specifying the lines29 to request and their configuration.30 31Description32===========33 34On success, the requesting process is granted exclusive access to the line35value, write access to the line configuration, and may receive events when36edges are detected on the line, all of which are described in more detail in37:ref:`gpio-v2-line-request`.38 39A number of lines may be requested in the one line request, and request40operations are performed on the requested lines by the kernel as atomically41as possible. e.g. gpio-v2-line-get-values-ioctl.rst will read all the42requested lines at once.43 44The state of a line, including the value of output lines, is guaranteed to45remain as requested until the returned file descriptor is closed. Once the46file descriptor is closed, the state of the line becomes uncontrolled from47the userspace perspective, and may revert to its default state.48 49Requesting a line already in use is an error (**EBUSY**).50 51Closing the ``chip_fd`` has no effect on existing line requests.52 53.. _gpio-v2-get-line-config-rules:54 55Configuration Rules56-------------------57 58For any given requested line, the following configuration rules apply:59 60The direction flags, ``GPIO_V2_LINE_FLAG_INPUT`` and61``GPIO_V2_LINE_FLAG_OUTPUT``, cannot be combined. If neither are set then62the only other flag that may be set is ``GPIO_V2_LINE_FLAG_ACTIVE_LOW``63and the line is requested "as-is" to allow reading of the line value64without altering the electrical configuration.65 66The drive flags, ``GPIO_V2_LINE_FLAG_OPEN_xxx``, require the67``GPIO_V2_LINE_FLAG_OUTPUT`` to be set.68Only one drive flag may be set.69If none are set then the line is assumed push-pull.70 71Only one bias flag, ``GPIO_V2_LINE_FLAG_BIAS_xxx``, may be set, and it72requires a direction flag to also be set.73If no bias flags are set then the bias configuration is not changed.74 75The edge flags, ``GPIO_V2_LINE_FLAG_EDGE_xxx``, require76``GPIO_V2_LINE_FLAG_INPUT`` to be set and may be combined to detect both rising77and falling edges. Requesting edge detection from a line that does not support78it is an error (**ENXIO**).79 80Only one event clock flag, ``GPIO_V2_LINE_FLAG_EVENT_CLOCK_xxx``, may be set.81If none are set then the event clock defaults to ``CLOCK_MONOTONIC``.82The ``GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE`` flag requires supporting hardware83and a kernel with ``CONFIG_HTE`` set. Requesting HTE from a device that84doesn't support it is an error (**EOPNOTSUPP**).85 86The :c:type:`debounce_period_us<gpio_v2_line_attribute>` attribute may only87be applied to lines with ``GPIO_V2_LINE_FLAG_INPUT`` set. When set, debounce88applies to both the values returned by gpio-v2-line-get-values-ioctl.rst and89the edges returned by gpio-v2-line-event-read.rst. If not90supported directly by hardware, debouncing is emulated in software by the91kernel. Requesting debounce on a line that supports neither debounce in92hardware nor interrupts, as required for software emulation, is an error93(**ENXIO**).94 95Requesting an invalid configuration is an error (**EINVAL**).96 97.. _gpio-v2-get-line-config-support:98 99Configuration Support100---------------------101 102Where the requested configuration is not directly supported by the underlying103hardware and driver, the kernel applies one of these approaches:104 105 - reject the request106 - emulate the feature in software107 - treat the feature as best effort108 109The approach applied depends on whether the feature can reasonably be emulated110in software, and the impact on the hardware and userspace if the feature is not111supported.112The approach applied for each feature is as follows:113 114============== ===========115Feature Approach116============== ===========117Bias best effort118Debounce emulate119Direction reject120Drive emulate121Edge Detection reject122============== ===========123 124Bias is treated as best effort to allow userspace to apply the same125configuration for platforms that support internal bias as those that require126external bias.127Worst case the line floats rather than being biased as expected.128 129Debounce is emulated by applying a filter to hardware interrupts on the line.130An edge event is generated after an edge is detected and the line remains131stable for the debounce period.132The event timestamp corresponds to the end of the debounce period.133 134Drive is emulated by switching the line to an input when the line should not135be actively driven.136 137Edge detection requires interrupt support, and is rejected if that is not138supported. Emulation by polling can still be performed from userspace.139 140In all cases, the configuration reported by gpio-v2-get-lineinfo-ioctl.rst141is the requested configuration, not the resulting hardware configuration.142Userspace cannot determine if a feature is supported in hardware, is143emulated, or is best effort.144 145Return Value146============147 148On success 0 and the :c:type:`request.fd<gpio_v2_line_request>` contains the149file descriptor for the request.150 151On error -1 and the ``errno`` variable is set appropriately.152Common error codes are described in error-codes.rst.153