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From: Sascha Hauer <s.hauer@pengutronix.de>
To: Barebox List <barebox@lists.infradead.org>
Subject: [PATCH 17/18] Documentation: Add documentation for device tree overlays
Date: Thu, 24 Jun 2021 10:52:22 +0200	[thread overview]
Message-ID: <20210624085223.14616-18-s.hauer@pengutronix.de> (raw)
In-Reply-To: <20210624085223.14616-1-s.hauer@pengutronix.de>

Document the recently gained device tree overlay features.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 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


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  parent reply	other threads:[~2021-06-24  8:54 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24  8:52 [PATCH v3 00/18] Apply device tree overlays to kernel tree Sascha Hauer
2021-06-24  8:52 ` [PATCH 01/18] of: of_copy_node(): Copy phandles as well Sascha Hauer
2021-06-24  8:52 ` [PATCH 02/18] of: Add function to duplicate a device tree Sascha Hauer
2021-06-24  8:52 ` [PATCH 03/18] fdt: Check blob size during unflattening Sascha Hauer
2021-06-24  8:52 ` [PATCH 04/18] firmware: make device_node argument non const Sascha Hauer
2021-06-24  8:52 ` [PATCH 05/18] libbb: Add find_path function Sascha Hauer
2021-06-24  8:52 ` [PATCH 06/18] firmware: consolidate ifdefs Sascha Hauer
2021-06-24  8:52 ` [PATCH 07/18] firmware: Add search path Sascha Hauer
2021-06-24  8:52 ` [PATCH 08/18] firmware: Fix device_node matching Sascha Hauer
2021-06-24  8:52 ` [PATCH 09/18] firmware: recognize by reproducible name Sascha Hauer
2021-06-24  8:52 ` [PATCH 10/18] blspec: Set firmware searchpath Sascha Hauer
2021-06-24  8:52 ` [PATCH 11/18] overlay: Add of_overlay_apply_file() Sascha Hauer
2021-06-24  8:52 ` [PATCH 12/18] firmware: Load from global search path Sascha Hauer
2021-06-24  8:52 ` [PATCH 13/18] blspec: Rework firmware load Sascha Hauer
2021-06-24  8:52 ` [PATCH 14/18] overlay: Add filters to choose which overlays to apply Sascha Hauer
2021-06-28 18:58   ` Michael Riesch
2021-06-28 20:13     ` Sascha Hauer
2021-06-24  8:52 ` [PATCH 15/18] blspec: Apply overlays from rootfs Sascha Hauer
2021-06-24  8:52 ` [PATCH 16/18] doc: devicetree: Refer to internal device tree also as live tree Sascha Hauer
2021-06-24  8:52 ` Sascha Hauer [this message]
2021-06-24  8:52 ` [PATCH 18/18] of_firmware: Fix handling of firmware-name property Sascha Hauer

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