Re: [PATCH 2/2] Documentation: user: barebox: mention generic dt 2nd stage support

[Sascha Hauer <sha@pengutronix.de>]

On Sun, Feb 06, 2022 at 12:19:30AM +0100, Ahmad Fatoum wrote:
> Most users interested in chainloading barebox will probably want to use
> the generic DT format for that: It will pass the checks the boot command
> may have and it will ensure the system is in the correct state, e.g.
> that caches are disabled.
> 
> Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
> ---
>  Documentation/user/barebox.rst | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/user/barebox.rst b/Documentation/user/barebox.rst
> index 8634d8e48eef..4abcf79c6d2a 100644
> --- a/Documentation/user/barebox.rst
> +++ b/Documentation/user/barebox.rst
> @@ -203,9 +203,21 @@ Starting barebox
>  Bringing barebox to a board for the first time is highly board specific, see your
>  board documentation for initial bringup.
>  
> -barebox binaries are, where possible, designed to be startable second stage from another
> -bootloader. For example, if you have U-Boot running on your board, you can start barebox
> -with U-Boot's ``bootm`` command:
> +For ARM and RISC-V, the barebox build can additionally generate a generic DT image
> +(enable ``CONFIG_BOARD_ARM_GENERIC_DT`` or ``CONFIG_BOARD_RISCV_GENERIC_DT``,
> +respectively). The resulting ``images/barebox-dt-2nd.img`` can be booted just
> +like a Linux kernel that is passed an external device tree. For example:
> +
> +.. code-block:: console
> +
> +  U-Boot: tftp $kernel_addr barebox-dt-2nd.img
> +  U-Boot: tftp $fdt_addr my-board.dtb
> +  U-Boot: booti $kernel_addr - $fdt_addr
> +
> +For non-DT enabled-bootloaders or other architectures, often the normal barebox
> +binaries can also be used as they are designed to be startable second stage
> +from another bootloader, where possible. For example, if you have U-Boot running
> +on your board, you can start barebox with U-Boot's ``bootm`` command:

Hm, that seems wrong. U-Boot's bootm command starts images generated
with U-Boot's mkimage tool. A raw barebox image cannot be started with
this command, one has to create a uImage from it before.

Sascha


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