mirror of
https://github.com/u-boot/u-boot.git
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doc: Bring in the FIT overlay information
Bring this file into the documentation. Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass
Heinrich Schuchardt
parent
51de69cda3
commit
6f6e8bb695
3 changed files with 228 additions and 225 deletions
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@ -1,225 +0,0 @@
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U-Boot FDT Overlay FIT usage
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============================
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Introduction
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------------
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In many cases it is desirable to have a single FIT image support a multitude
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of similar boards and their expansion options. The same kernel on DT enabled
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platforms can support this easily enough by providing a DT blob upon boot
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that matches the desired configuration.
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This document focuses on specifically using overlays as part of a FIT image.
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General information regarding overlays including its syntax and building it
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can be found in doc/README.fdt-overlays
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Configuration without overlays
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------------------------------
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Take a hypothetical board named 'foo' where there are different supported
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revisions, reva and revb. Assume that both board revisions can use add a bar
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add-on board, while only the revb board can use a baz add-on board.
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Without using overlays the configuration would be as follows for every case.
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/dts-v1/;
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/ {
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images {
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kernel {
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data = /incbin/("./zImage");
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type = "kernel";
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arch = "arm";
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os = "linux";
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load = <0x82000000>;
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entry = <0x82000000>;
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};
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fdt-1 {
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data = /incbin/("./foo-reva.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-2 {
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data = /incbin/("./foo-revb.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-3 {
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data = /incbin/("./foo-reva-bar.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-4 {
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data = /incbin/("./foo-revb-bar.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-5 {
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data = /incbin/("./foo-revb-baz.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-6 {
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data = /incbin/("./foo-revb-bar-baz.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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};
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configurations {
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default = "foo-reva.dtb;
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foo-reva.dtb {
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kernel = "kernel";
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fdt = "fdt-1";
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};
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foo-revb.dtb {
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kernel = "kernel";
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fdt = "fdt-2";
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};
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foo-reva-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-3";
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};
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foo-revb-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-4";
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};
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foo-revb-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-5";
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};
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foo-revb-bar-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-6";
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};
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};
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};
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Note the blob needs to be compiled for each case and the combinatorial explosion of
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configurations. A typical device tree blob is in the low hunderds of kbytes so a
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multitude of configuration grows the image quite a bit.
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Booting this image is done by using
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# bootm <addr>#<config>
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Where config is one of:
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foo-reva.dtb, foo-revb.dtb, foo-reva-bar.dtb, foo-revb-bar.dtb,
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foo-revb-baz.dtb, foo-revb-bar-baz.dtb
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This selects the DTB to use when booting.
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Configuration using overlays
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----------------------------
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Device tree overlays can be applied to a base DT and result in the same blob
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being passed to the booting kernel. This saves on space and avoid the combinatorial
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explosion problem.
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/dts-v1/;
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/ {
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images {
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kernel {
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data = /incbin/("./zImage");
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type = "kernel";
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arch = "arm";
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os = "linux";
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load = <0x82000000>;
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entry = <0x82000000>;
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};
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fdt-1 {
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data = /incbin/("./foo.dtb");
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type = "flat_dt";
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arch = "arm";
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load = <0x87f00000>;
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};
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fdt-2 {
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data = /incbin/("./reva.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-3 {
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data = /incbin/("./revb.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-4 {
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data = /incbin/("./bar.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-5 {
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data = /incbin/("./baz.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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};
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configurations {
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default = "foo-reva.dtb;
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foo-reva.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-2";
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};
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foo-revb.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3";
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};
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foo-reva-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-2", "fdt-4";
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};
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foo-revb-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-4";
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};
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foo-revb-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-5";
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};
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foo-revb-bar-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-4", "fdt-5";
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};
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bar {
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fdt = "fdt-4";
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};
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baz {
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fdt = "fdt-5";
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};
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};
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};
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Booting this image is exactly the same as the non-overlay example.
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u-boot will retrieve the base blob and apply the overlays in sequence as
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they are declared in the configuration.
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Note the minimum amount of different DT blobs, as well as the requirement for
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the DT blobs to have a load address; the overlay application requires the blobs
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to be writeable.
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Configuration using overlays and feature selection
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--------------------------------------------------
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Although the configuration in the previous section works is a bit inflexible
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since it requires all possible configuration options to be laid out before
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hand in the FIT image. For the add-on boards the extra config selection method
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might make sense.
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Note the two bar & baz configuration nodes. To boot a reva board with
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the bar add-on board enabled simply use:
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# bootm <addr>#foo-reva.dtb#bar
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While booting a revb with bar and baz is as follows:
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# bootm <addr>#foo-revb.dtb#bar#baz
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The limitation for a feature selection configuration node is that a single
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fdt option is currently supported.
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Pantelis Antoniou
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pantelis.antoniou@konsulko.com
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12/6/2017
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@ -16,3 +16,4 @@ doc/uImage.FIT
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signature
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verified-boot
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beaglebone_vboot
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overlay-fdt-boot
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227
doc/usage/fit/overlay-fdt-boot.rst
Normal file
227
doc/usage/fit/overlay-fdt-boot.rst
Normal file
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@ -0,0 +1,227 @@
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.. SPDX-License-Identifier: GPL-2.0+
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U-Boot FDT Overlay FIT usage
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============================
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Introduction
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------------
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In many cases it is desirable to have a single FIT image support a multitude
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of similar boards and their expansion options. The same kernel on DT enabled
|
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platforms can support this easily enough by providing a DT blob upon boot
|
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that matches the desired configuration.
|
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|
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This document focuses on specifically using overlays as part of a FIT image.
|
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General information regarding overlays including its syntax and building it
|
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can be found in doc/README.fdt-overlays
|
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|
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Configuration without overlays
|
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------------------------------
|
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|
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Take a hypothetical board named 'foo' where there are different supported
|
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revisions, reva and revb. Assume that both board revisions can use add a bar
|
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add-on board, while only the revb board can use a baz add-on board.
|
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|
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Without using overlays the configuration would be as follows for every case::
|
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/dts-v1/;
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/ {
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images {
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kernel {
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data = /incbin/("./zImage");
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type = "kernel";
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arch = "arm";
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os = "linux";
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load = <0x82000000>;
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entry = <0x82000000>;
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};
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fdt-1 {
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data = /incbin/("./foo-reva.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-2 {
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data = /incbin/("./foo-revb.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-3 {
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data = /incbin/("./foo-reva-bar.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-4 {
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data = /incbin/("./foo-revb-bar.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-5 {
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data = /incbin/("./foo-revb-baz.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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fdt-6 {
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data = /incbin/("./foo-revb-bar-baz.dtb");
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type = "flat_dt";
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arch = "arm";
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};
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};
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configurations {
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default = "foo-reva.dtb;
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foo-reva.dtb {
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kernel = "kernel";
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fdt = "fdt-1";
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};
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foo-revb.dtb {
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kernel = "kernel";
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fdt = "fdt-2";
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};
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foo-reva-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-3";
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};
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foo-revb-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-4";
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};
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foo-revb-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-5";
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};
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foo-revb-bar-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-6";
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};
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};
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};
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Note the blob needs to be compiled for each case and the combinatorial explosion of
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configurations. A typical device tree blob is in the low hunderds of kbytes so a
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multitude of configuration grows the image quite a bit.
|
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|
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Booting this image is done by using::
|
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|
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# bootm <addr>#<config>
|
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|
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Where config is one of::
|
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|
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foo-reva.dtb, foo-revb.dtb, foo-reva-bar.dtb, foo-revb-bar.dtb,
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foo-revb-baz.dtb, foo-revb-bar-baz.dtb
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This selects the DTB to use when booting.
|
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|
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Configuration using overlays
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----------------------------
|
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|
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Device tree overlays can be applied to a base DT and result in the same blob
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being passed to the booting kernel. This saves on space and avoid the combinatorial
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explosion problem::
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|
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/dts-v1/;
|
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/ {
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images {
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kernel {
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data = /incbin/("./zImage");
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type = "kernel";
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arch = "arm";
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os = "linux";
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load = <0x82000000>;
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entry = <0x82000000>;
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};
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fdt-1 {
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data = /incbin/("./foo.dtb");
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type = "flat_dt";
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arch = "arm";
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load = <0x87f00000>;
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};
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fdt-2 {
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data = /incbin/("./reva.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-3 {
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data = /incbin/("./revb.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-4 {
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data = /incbin/("./bar.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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fdt-5 {
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data = /incbin/("./baz.dtbo");
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type = "flat_dt";
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arch = "arm";
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load = <0x87fc0000>;
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};
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};
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configurations {
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default = "foo-reva.dtb;
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foo-reva.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-2";
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};
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foo-revb.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3";
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};
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foo-reva-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-2", "fdt-4";
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};
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foo-revb-bar.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-4";
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};
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foo-revb-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-5";
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};
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foo-revb-bar-baz.dtb {
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kernel = "kernel";
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fdt = "fdt-1", "fdt-3", "fdt-4", "fdt-5";
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};
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bar {
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fdt = "fdt-4";
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};
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baz {
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fdt = "fdt-5";
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};
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};
|
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};
|
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|
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Booting this image is exactly the same as the non-overlay example.
|
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u-boot will retrieve the base blob and apply the overlays in sequence as
|
||||
they are declared in the configuration.
|
||||
|
||||
Note the minimum amount of different DT blobs, as well as the requirement for
|
||||
the DT blobs to have a load address; the overlay application requires the blobs
|
||||
to be writeable.
|
||||
|
||||
Configuration using overlays and feature selection
|
||||
--------------------------------------------------
|
||||
|
||||
Although the configuration in the previous section works is a bit inflexible
|
||||
since it requires all possible configuration options to be laid out before
|
||||
hand in the FIT image. For the add-on boards the extra config selection method
|
||||
might make sense.
|
||||
|
||||
Note the two bar & baz configuration nodes. To boot a reva board with
|
||||
the bar add-on board enabled simply use::
|
||||
|
||||
=> bootm <addr>#foo-reva.dtb#bar
|
||||
|
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While booting a revb with bar and baz is as follows::
|
||||
|
||||
=> bootm <addr>#foo-revb.dtb#bar#baz
|
||||
|
||||
The limitation for a feature selection configuration node is that a single
|
||||
fdt option is currently supported.
|
||||
|
||||
.. sectionauthor:: Pantelis Antoniou <pantelis.antoniou@konsulko.com>, 12/6/2017
|
||||
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