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From: Sascha Hauer <s.hauer@pengutronix.de>
To: Barebox List <barebox@lists.infradead.org>
Subject: [PATCH 16/17] Documentation: Add documentation for device tree overlays
Date: Wed, 23 Jun 2021 07:16:31 +0200	[thread overview]
Message-ID: <20210623051632.30253-17-s.hauer@pengutronix.de> (raw)
In-Reply-To: <20210623051632.30253-1-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 | 37 +++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Documentation/user/devicetree.rst b/Documentation/user/devicetree.rst
index 4be6a1e703..d78394b7aa 100644
--- a/Documentation/user/devicetree.rst
+++ b/Documentation/user/devicetree.rst
@@ -75,3 +75,40 @@ 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 using
+  bootloader spec this variable will be temporarily overwritten with
+  ``$mountpoint/overlays`` where ``$mountpoint`` is the path where the filesystem
+  containing the bootloader spec entries are located.
+``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. When empty, all files are applied.
-- 
2.29.2


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  parent reply	other threads:[~2021-06-23  5:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-23  5:16 [PATCH v2 00/17] Apply device tree overlays to kernel tree Sascha Hauer
2021-06-23  5:16 ` [PATCH 01/17] fdt: Check blob size during unflattening Sascha Hauer
2021-06-23  5:16 ` [PATCH 02/17] firmware: make device_node argument non const Sascha Hauer
2021-06-23  5:16 ` [PATCH 03/17] libbb: Add find_path function Sascha Hauer
2021-06-23  5:16 ` [PATCH 04/17] firmware: consolidate ifdefs Sascha Hauer
2021-06-23  5:16 ` [PATCH 05/17] firmware: Add search path Sascha Hauer
2021-06-23  5:16 ` [PATCH 06/17] firmware: Fix device_node matching Sascha Hauer
2021-06-23  5:16 ` [PATCH 07/17] firmware: recognize by reproducible name Sascha Hauer
2021-06-23  5:16 ` [PATCH 08/17] blspec: Set firmware searchpath Sascha Hauer
2021-06-23  5:16 ` [PATCH 09/17] overlay: only apply compatible trees Sascha Hauer
2021-06-23  5:16 ` [PATCH 10/17] overlay: Add of_overlay_apply_file() Sascha Hauer
2021-06-23  5:16 ` [PATCH 11/17] firmware: Load from global search path Sascha Hauer
2021-06-23  5:16 ` [PATCH 12/17] blspec: Rework firmware load Sascha Hauer
2021-06-23  5:16 ` [PATCH 13/17] of_overlay: apply overlays during booting Sascha Hauer
2021-06-23  5:16 ` [PATCH 14/17] blspec: Apply overlays from rootfs Sascha Hauer
2021-06-23  5:16 ` [PATCH 15/17] doc: devicetree: Refer to internal device tree also as live tree Sascha Hauer
2021-06-23  5:16 ` Sascha Hauer [this message]
2021-06-23  6:13   ` [PATCH 16/17] Documentation: Add documentation for device tree overlays Ahmad Fatoum
2021-06-23 19:37     ` Trent Piepho
2021-06-24  8:48       ` Sascha Hauer
2021-06-23  5:16 ` [PATCH 17/17] of_firmware: Fix handling of firmware-name property Sascha Hauer
  -- strict thread matches above, loose matches on Subject: below --
2021-03-10 13:28 [PATCH 00/17] Apply device tree overlays to kernel tree Sascha Hauer
2021-03-10 13:28 ` [PATCH 16/17] Documentation: Add documentation for device tree overlays Sascha Hauer

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