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The documentation does not make sufficiently clear that the uAPI deals with logical line values, nor does it describe the influence of the active low flag on the mapping between physical and logical line values. Clarify the relationship between physical and logical line values and the effect of the active low flag for ioctls passing line values. Suggested-by: David C. Rankin <drankinatty@gmail.com> Signed-off-by: Kent Gibson <warthog618@gmail.com> Link: https://lore.kernel.org/r/20240610092157.9147-2-warthog618@gmail.com Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
59 lines
1.7 KiB
ReStructuredText
59 lines
1.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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.. _GPIO_V2_LINE_GET_VALUES_IOCTL:
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*****************************
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GPIO_V2_LINE_GET_VALUES_IOCTL
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*****************************
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Name
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====
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GPIO_V2_LINE_GET_VALUES_IOCTL - Get the values of requested lines.
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Synopsis
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========
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.. c:macro:: GPIO_V2_LINE_GET_VALUES_IOCTL
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``int ioctl(int req_fd, GPIO_V2_LINE_GET_VALUES_IOCTL, struct gpio_v2_line_values *values)``
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Arguments
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=========
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``req_fd``
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The file descriptor of the GPIO character device, as returned in the
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:c:type:`request.fd<gpio_v2_line_request>` by gpio-v2-get-line-ioctl.rst.
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``values``
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The :c:type:`line_values<gpio_v2_line_values>` to get with the ``mask`` set
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to indicate the subset of requested lines to get.
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Description
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===========
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Get the values of requested lines.
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The values returned are logical, indicating if the line is active or inactive.
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The ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` flag controls the mapping between physical
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values (high/low) and logical values (active/inactive).
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If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is not set then high is active and low is
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inactive. If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is set then low is active and
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high is inactive.
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The values of both input and output lines may be read.
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For output lines, the value returned is driver and configuration dependent and
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may be either the output buffer (the last requested value set) or the input
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buffer (the actual level of the line), and depending on the hardware and
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configuration these may differ.
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Return Value
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============
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On success 0 and the corresponding :c:type:`values.bits<gpio_v2_line_values>`
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contain the value read.
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On error -1 and the ``errno`` variable is set appropriately.
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Common error codes are described in error-codes.rst.
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