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Documentation: gpio: Clarify effect of active low flag on line values

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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>
This commit is contained in:
Kent Gibson 2024-06-10 17:21:56 +08:00 committed by Bartosz Golaszewski
parent 3ff1180a39
commit 5ca84d416e
4 changed files with 28 additions and 0 deletions
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7
Documentation/userspace-api/gpio/gpio-handle-get-line-values-ioctl.rst
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@ -36,6 +36,13 @@ Description
Get the values of all requested lines.
The values returned are logical, indicating if the line is active or inactive.
The ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` flag controls the mapping between physical
values (high/low) and logical values (active/inactive).
If ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` is not set then high is active and
low is inactive. If ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` is set then low is active
and high is inactive.
The values of both input and output lines may be read.
For output lines, the value returned is driver and configuration dependent and

7
Documentation/userspace-api/gpio/gpio-handle-set-line-values-ioctl.rst
View File

@ -36,6 +36,13 @@ Description
Set the values of all requested output lines.
The values set are logical, indicating if the line is to be active or inactive.
The ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` flag controls the mapping between logical
values (active/inactive) and physical values (high/low).
If ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` is not set then active is high and
inactive is low. If ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` is set then active is low
and inactive is high.
Only the values of output lines may be set.
Attempting to set the value of input lines is an error (**EPERM**).

7
Documentation/userspace-api/gpio/gpio-v2-line-get-values-ioctl.rst
View File

@ -34,6 +34,13 @@ Description
Get the values of requested lines.
The values returned are logical, indicating if the line is active or inactive.
The ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` flag controls the mapping between physical
values (high/low) and logical values (active/inactive).
If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is not set then high is active and low is
inactive. If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is set then low is active and
high is inactive.
The values of both input and output lines may be read.
For output lines, the value returned is driver and configuration dependent and

7
Documentation/userspace-api/gpio/gpio-v2-line-set-values-ioctl.rst
View File

@ -35,6 +35,13 @@ Description
Set the values of requested output lines.
The values set are logical, indicating if the line is to be active or inactive.
The ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` flag controls the mapping between logical
values (active/inactive) and physical values (high/low).
If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is not set then active is high and inactive
is low. If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is set then active is low and
inactive is high.
Only the values of output lines may be set.
Attempting to set the value of an input line is an error (**EPERM**).