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Drop the docs in the README as it is out of date.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 ---
Changes in v8: - Drop the devicetree docs in the README - Move board-config changes to a separate patch
Changes in v7: - Add new patch to add a Kconfig for boards with a prior stage
README | 29 ----------------------------- dts/Kconfig | 33 ++++++++++++++++++++++++++++----- lib/fdtdec.c | 1 + 3 files changed, 29 insertions(+), 34 deletions(-)
diff --git a/README b/README index 056b717557b..3496bef7774 100644 --- a/README +++ b/README @@ -646,35 +646,6 @@ The following options need to be configured: which adds regex support to some commands, as for example "env grep" and "setexpr".
-- Device tree: - CONFIG_OF_CONTROL - If this variable is defined, U-Boot will use a device tree - to configure its devices, instead of relying on statically - compiled #defines in the board file. This option is - experimental and only available on a few boards. The device - tree is available in the global data as gd->fdt_blob. - - U-Boot needs to get its device tree from somewhere. This can - be done using one of the three options below: - - CONFIG_OF_SEPARATE - If this variable is defined, U-Boot will build a device tree - binary. It will be called u-boot.dtb. Architecture-specific - code will locate it at run-time. Generally this works by: - - cat u-boot.bin u-boot.dtb >image.bin - - and in fact, U-Boot does this for you, creating a file called - u-boot-dtb.bin which is useful in the common case. You can - still use the individual files if you need something more - exotic. - - CONFIG_OF_BOARD - If this variable is defined, U-Boot will use the device tree - provided by the board at runtime instead of embedding one with - the image. Only boards defining board_fdt_blob_setup() support - this option (see include/fdtdec.h file). - - Watchdog: CONFIG_WATCHDOG If this variable is defined, it enables watchdog diff --git a/dts/Kconfig b/dts/Kconfig index 5dcc79d5192..e57ce84b98d 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" diff --git a/lib/fdtdec.c b/lib/fdtdec.c index 118c100b389..280cda61a72 100644 --- a/lib/fdtdec.c +++ b/lib/fdtdec.c @@ -1595,6 +1595,7 @@ int fdtdec_set_carveout(void *blob, const char *node, const char *prop_name, return 0; }
+/* TODO(sjg@chromium.org): This function should not be weak */ __weak int fdtdec_board_setup(const void *fdt_blob) { return 0;