diff options
| author | Simon Glass <sjg@chromium.org> | 2021-12-16 20:59:35 -0700 |
|---|---|---|
| committer | Tom Rini <trini@konsulko.com> | 2021-12-23 10:24:40 -0500 |
| commit | 275b4832f6bf91ca723430efe93be06e4f07430d (patch) | |
| tree | 5e06b1267d68dbcbff15bea3cde1e2458340ee03 /dts | |
| parent | ff66e7bb73233a4decfcdb66b7a858399dbccf50 (diff) | |
fdt: Add a Kconfig for boards with a prior stage
When U-Boot is started from another firmware program, not just a prior
phase of U-Boot, special behaviour is typically used. In particular, the
device tree may come from that prior stage.
At present this is sort-of indicated by OF_BOARD, although the
correlation is not 1:1, since that option simply means that the board has
a custom mechanism for obtaining the device tree. For example, sandbox
defines OF_BOARD. Also the board_fdt_blob_setup() function can in fact
make use of the devicetree in U-Boot if it wishes, as used by
dragonboard410c until very recently.
Add an explicit Kconfig for this situation. Update the OF_BOARD option to
more-accurately reflect what it is doing, e.g. for sandbox.
Drop the docs in the README as it is out of date.
Signed-off-by: Simon Glass <sjg@chromium.org>
Diffstat (limited to 'dts')
| -rw-r--r-- | dts/Kconfig | 33 |
1 files changed, 28 insertions, 5 deletions
diff --git a/dts/Kconfig b/dts/Kconfig index 5dcc79d519..e57ce84b98 100644 --- a/dts/Kconfig +++ b/dts/Kconfig @@ -98,13 +98,36 @@ endchoice config OF_BOARD bool "Provided by the board (e.g a previous loader) at runtime" - default y if SANDBOX + default y if SANDBOX || OF_HAS_PRIOR_STAGE help - If this option is enabled, the device tree will be provided by - the board at runtime if the board supports it. The device tree bundled - with the image (if any) will be overridden / ignored. + If this option is enabled, the device tree is provided at runtime by + a custom function called board_fdt_blob_setup(). The board must + implement this function if it wishes to provide special behaviour. - A device tree file must be provided in the tree. + With this option, the device tree build by U-Boot may be overridden or + ignored. See OF_HAS_PRIOR_STAGE. + + Note: Boards which use this to handle a device tree passed from an + earlier stage should enable OF_HAS_PRIOR_STAGE. + +config OF_HAS_PRIOR_STAGE + bool + help + Indicates that a prior stage of the firmware (before U-Boot proper) + makes use of device tree and this board normally boots with that prior + stage, that provides a devicetree to U-Boot. + + This means that the device tree built in U-Boot should not be packaged + in the firmware image. Instead, the prior stage's device tree should + be so packaged. At runtime, the prior stage reads this, does any + necessary fix-ups, then passes it to U-Boot. See OF_BOARD. + + This option does not preclude using the U-Boot device tree, e.g. for + development purposes, but it is not recommended, and likely will not + even work, for production systems. + + Note: This option must be set in Kconfig and cannot be enabled or + disabled in the board's defconfig file. config DEFAULT_DEVICE_TREE string "Default Device Tree for DT control" |