diff options
Diffstat (limited to 'Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst')
| -rw-r--r-- | Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst b/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst index c8256afe306e..9112a9d31174 100644 --- a/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst +++ b/Documentation/userspace-api/gpio/gpio-get-linehandle-ioctl.rst @@ -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 ============ |