bybrooklyn/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-04-18 23:03:57 -04:00
Code Issues Packages Projects Releases Wiki Activity

Documentation: gpio: describe uAPI behaviour for unsupported config

Browse Source 
The existing uAPI documentation does not adequately describe how the kernel
handles the case where the underlying hardware or driver does not support
the requested configuration.

Add a Configuration Support section describing that behaviour to both the
v1 and v2 documentation, and better document the errors returned where the
requested configuration cannot be supported.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
This commit is contained in:
Kent Gibson
2024-01-23 21:38:28 +08:00
committed by Bartosz Golaszewski
parent 3473765920
commit 42969726a1
6 changed files with 106 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst
View File

@@ -76,6 +76,45 @@ If no bias flags are set then the bias configuration is not changed.
Requesting an invalid configuration is an error (**EINVAL**).
.. _gpio-get-linehandle-config-support:
Configuration Support
---------------------
Where the requested configuration is not directly supported by the underlying
hardware and driver, the kernel applies one of these approaches:
- reject the request
- emulate the feature in software
- treat the feature as best effort
The approach applied depends on whether the feature can reasonably be emulated
in software, and the impact on the hardware and userspace if the feature is not
supported.
The approach applied for each feature is as follows:
============== ===========
Feature Approach
============== ===========
Bias best effort
Direction reject
Drive emulate
============== ===========
Bias is treated as best effort to allow userspace to apply the same
configuration for platforms that support internal bias as those that require
external bias.
Worst case the line floats rather than being biased as expected.
Drive is emulated by switching the line to an input when the line should not
be driven.
In all cases, the configuration reported by gpio-get-lineinfo-ioctl.rst
is the requested configuration, not the resulting hardware configuration.
Userspace cannot determine if a feature is supported in hardware, is
emulated, or is best effort.
Return Value
============