Document the recently gained device tree overlay features. Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> --- Documentation/user/devicetree.rst | 43 +++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/Documentation/user/devicetree.rst b/Documentation/user/devicetree.rst index 4be6a1e703..91afffdcda 100644 --- a/Documentation/user/devicetree.rst +++ b/Documentation/user/devicetree.rst @@ -75,3 +75,46 @@ It is important to know that these commands normally work on the internal devicetree. If you want to modify the devicetree the kernel is started with see the -f options to of_property and of_node. This option will register the operation for later execution on the Kernel devicetree. + +Device tree overlays +-------------------- + +barebox has support for device tree overlays. barebox knows two different trees, +the live tree and the device tree the kernel is started with. Both can be applied +overlays to. + +Device tree overlays on the live tree +..................................... + +While the live tree can be patched by board code, barebox does not +detect any changes to the live tree. To let the overlays have any effect, board +code must make sure the live tree is patched before the devices are instanciated +from it. + +Device tree overlays on the kernel device tree +.............................................. + +Overlays can be applied to the kernel device tree before it is handed over to +the kernel. The behaviour is controlled by different variables: + +``global.of.overlay.dir`` + Overlays are read from this directory. barebox will try to apply all overlays + found here if not limited by one of the other variables below. When the path + given here is an absolute path it is used as is. A relative path is relative + to ``/`` or relative to the rootfs when using bootloader spec. +``global.of.overlay.compatible`` + This is a space separated list of compatibles. Only overlays matching one of + these compatibles will be applied. When this list is empty then all overlays + will be applied. Overlays that don't have a compatible are considered being + always compatible. +``global.of.overlay.filepattern`` + This is a space separated list of file patterns. An overlay is only applied + when its filename matches one of the patterns. The patterns can contain + ``*`` and ``?`` as wildcards. The default is ``*`` which means all files are + applied. +``global.of.overlay.filter`` + This is a space separated list of filters to apply. There are two generic filters: + ``filepattern`` matches ``global.of.overlay.filepattern`` above, ``compatible`` matches + ``global.of.overlay.compatible`` above. The default is ``filepattern compatible`` + which means the two generic filters are active. This list may be replaced or + supplemented by board specific filters. -- 2.29.2 _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
