mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-28 22:13:08 +00:00
56fc7032e1
Pull some information regarding overlays from commit messages and put them directly within the documentation. Also add some information regarding required dtc version to properly use overlays. Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com> Acked-by: Simon Glass <sjg@chromium.org>
114 lines
2.7 KiB
Text
114 lines
2.7 KiB
Text
U-Boot FDT Overlay usage
|
|
=============================================
|
|
|
|
Overlays Syntax
|
|
---------------
|
|
|
|
Overlays require slightly different syntax compared to traditional overlays.
|
|
Please refer to dt-object-internal.txt in the dtc sources for information
|
|
regarding the internal format of overlays:
|
|
https://git.kernel.org/pub/scm/utils/dtc/dtc.git/tree/Documentation/dt-object-internal.txt
|
|
|
|
Building Overlays
|
|
-----------------
|
|
|
|
In a nutshell overlays provides a means to manipulate a symbol a previous dtb
|
|
or overlay has defined. It requires both the base and all the overlays
|
|
to be compiled with the -@ command line switch so that symbol information is
|
|
included.
|
|
|
|
Note support for -@ option can only be found in dtc version 1.4.4 or newer.
|
|
Only version 4.14 or higher of the Linux kernel includes a built in version
|
|
of dtc that meets this requirement.
|
|
|
|
Building an overlay follows the same process as building a traditional dtb.
|
|
|
|
For example:
|
|
|
|
base.dts
|
|
--------
|
|
|
|
/dts-v1/;
|
|
/ {
|
|
foo: foonode {
|
|
foo-property;
|
|
};
|
|
};
|
|
|
|
$ dtc -@ -I dts -O dtb -o base.dtb base.dts
|
|
|
|
bar.dts
|
|
-------
|
|
|
|
/dts-v1/;
|
|
/plugin/;
|
|
/ {
|
|
fragment@1 {
|
|
target = <&foo>;
|
|
__overlay__ {
|
|
overlay-1-property;
|
|
bar: barnode {
|
|
bar-property;
|
|
};
|
|
};
|
|
};
|
|
};
|
|
|
|
$ dtc -@ -I dts -O dtb -o bar.dtb bar.dts
|
|
|
|
Ways to Utilize Overlays in U-boot
|
|
----------------------------------
|
|
|
|
There are two ways to apply overlays in U-boot.
|
|
1. Include and define overlays within a FIT image and have overlays
|
|
automatically applied.
|
|
|
|
2. Manually load and apply overlays
|
|
|
|
The remainder of this document will discuss using overlays via the manual
|
|
approach. For information on using overlays as part of a FIT image please see:
|
|
doc/uImage.FIT/overlay-fdt-boot.txt
|
|
|
|
Manually Loading and Applying Overlays
|
|
--------------------------------------
|
|
|
|
1. Figure out where to place both the base device tree blob and the
|
|
overlay. Make sure you have enough space to grow the base tree without
|
|
overlapping anything.
|
|
|
|
=> setenv fdtaddr 0x87f00000
|
|
=> setenv fdtovaddr 0x87fc0000
|
|
|
|
2. Load the base blob and overlay blobs
|
|
|
|
=> load ${devtype} ${bootpart} ${fdtaddr} ${bootdir}/base.dtb
|
|
=> load ${devtype} ${bootpart} ${fdtovaddr} ${bootdir}/overlay.dtb
|
|
|
|
3. Set it as the working fdt tree.
|
|
|
|
=> fdtaddr $fdtaddr
|
|
|
|
4. Grow it enough so it can 'fit' all the applied overlays
|
|
|
|
=> fdt resize 8192
|
|
|
|
5. You are now ready to apply the overlay.
|
|
|
|
=> fdt apply $fdtovaddr
|
|
|
|
6. Boot system like you would do with a traditional dtb.
|
|
|
|
For bootm:
|
|
|
|
=> bootm ${kerneladdr} - ${fdtaddr}
|
|
|
|
For bootz:
|
|
|
|
=> bootz ${kerneladdr} - ${fdtaddr}
|
|
|
|
Please note that in case of an error, both the base and overlays are going
|
|
to be invalidated, so keep copies to avoid reloading.
|
|
|
|
Pantelis Antoniou
|
|
pantelis.antoniou@konsulko.com
|
|
11/7/2017
|