[PATCH 3/3] common: fdt: hand over original fdt bootargs into board chosen handler

[Quentin Schulz]

Hi Dmitry,

On 12/19/24 10:42 PM, Dmitry Rokosov wrote:
> Sometimes, it is necessary to provide an additional bootargs string to
> the kernel command line.
> 
> We have a real scenario where one U-Boot blob needs to boot several
> kernel images: the vendor-patched kernel image and the latest upstream
> kernel image. The Amlogic (Meson architecture) tty driver has different
> tty suffixes in these kernels: the vendor uses 'ttySx', while the
> upstream implementation uses 'ttyAMLx'. The initial console setup is
> provided to the kernel using the kernel command line (bootargs). For the
> vendor kernel, we should use 'console=ttyS0,115200', while for the
> upstream kernel, it must be 'console=ttyAML0,115200'. This means we have
> to use different command line strings depending on the kernel version.
> 

Can't you have both in bootargs to handle both versions of the kernel 
with the same bootargs?

> To resolve this issue, we cannot use the CMDLINE_EXTEND kernel
> configuration because it is considered legacy and is not supported for
> the arm64 architecture. CMDLINE_EXTEND is outdated primarily because we
> can provide additional command line strings through the
> 'chosen/bootargs' FDT node. However, U-Boot uses this node to inject the
> U-Boot bootargs environment variable content, which results in U-Boot
> silently overriding all data in the 'chosen/bootargs' node. While we do
> have the board_fdt_chosen_bootargs() board hook to address such issues,
> this function lacks any FDT context, such as the original value of the
> 'chosen/bootargs' node.
> 
> This patch introduces a read-only (RO) fdt_property argument to
> board_fdt_chosen_bootargs() to share the original 'chosen/bootargs' data
> with the board code. Consequently, the board developer can decide how to
> handle this information for their board setup: whether to drop it or
> merge it with the bootargs environment.
> 
> Signed-off-by: Dmitry Rokosov <ddrokosov at salutedevices.com>
> ---
>   boot/fdt_support.c    | 5 +++--
>   include/fdt_support.h | 4 +++-
>   2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> index 2c39b2dd14b7c447bc4c7c8fad64e22cb00e88e0..49efeec3681f7c97341ccdce596bcaa4e1f037eb 100644
> --- a/boot/fdt_support.c
> +++ b/boot/fdt_support.c
> @@ -321,7 +321,7 @@ int fdt_kaslrseed(void *fdt, bool overwrite)
>    * board_fdt_chosen_bootargs - boards may override this function to use
>    *                             alternative kernel command line arguments
>    */
> -__weak const char *board_fdt_chosen_bootargs(void)
> +__weak const char *board_fdt_chosen_bootargs(const struct fdt_property *fdt_ba)
>   {
>   	return env_get("bootargs");
>   }
> @@ -364,7 +364,8 @@ int fdt_chosen(void *fdt)
>   		}
>   	}
>   
> -	str = board_fdt_chosen_bootargs();
> +	str = board_fdt_chosen_bootargs(fdt_get_property(fdt, nodeoffset,
> +							 "bootargs", NULL));
>   
>   	if (str) {
>   		err = fdt_setprop(fdt, nodeoffset, "bootargs", str,
> diff --git a/include/fdt_support.h b/include/fdt_support.h
> index f481881ce640797e0f6204d599f008d0e5dc2bf7..7731feba5f068f82c8ee25f18a9f0e57729e2bd8 100644
> --- a/include/fdt_support.h
> +++ b/include/fdt_support.h
> @@ -231,12 +231,14 @@ int board_rng_seed(struct abuf *buf);
>   /**
>    * board_fdt_chosen_bootargs() - arbitrarily amend fdt kernel command line
>    *
> + * @fdt_ba: FDT chosen/bootargs from the kernel image if available
> + *

Missing leading /

/chosen/bootargs

+property
to highlight what this path refers to.

Makes sense to me otherwise!

With those changes,
Reviewed-by: Quentin Schulz <quentin.schulz at cherry.de>

Thanks!
Quentin