[PATCH] cmd: fdt: use U-Boot's FDT by default

[E Shattow]

Hi Caleb, the problem here is hidden conditional behavior.

On Sat, Aug 31, 2024 at 9:56 AM Caleb Connolly
<caleb.connolly at linaro.org> wrote:
>
> When using the FDT command to inspect an arbitrary FDT in memory, it
> will always be necessary to explicitly set the FDT address. However it
> is also quite likely that the command is being used to inspect U-Boot's
> own FDT. Simplify that common workflow of running "fdt addr -c" to get
> the control address and set it by just making $fdtcontroladdr the
> default FDT if there isn't one.
>
> Signed-off-by: Caleb Connolly <caleb.connolly at linaro.org>
> ---
>  cmd/fdt.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/cmd/fdt.c b/cmd/fdt.c
> index d16b141ce32d..8909706e2483 100644
> --- a/cmd/fdt.c
> +++ b/cmd/fdt.c
> @@ -276,8 +276,17 @@ static int do_fdt(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
>
>                 return CMD_RET_SUCCESS;
>         }
>
> +       /* Try using U-Boot's FDT by default */
> +       if (!working_fdt) {
> +               struct fdt_header *addr;
> +
> +               addr = (void *)env_get_hex("fdtcontroladdr", 0);
> +               if (addr && fdt_check_header(&addr))
> +                       set_working_fdt_addr((phys_addr_t)addr);
> +       }
> +
>         if (!working_fdt) {
>                 puts("No FDT memory address configured. Please configure\n"
>                      "the FDT address via \"fdt addr <address>\" command.\n"
>                      "Aborting!\n");
> --
> 2.46.0
>

The use of `fdt` command in the default action might be depended on by
some userspace script as a success/fail result. I don't imagine what
that might possibly be, just that the logic of scripts in u-boot
depend on that pattern of use.

Secondly there would need to be a warning to the user that some hidden
conditional action is being applied? i.e. "No valid FDT address is
configured to $fdt_addr_r or $fdt_addr so now configuring to use
$fdtcontroladdr instead." or however you would phrase that.

Otherwise I agree improvement to the fdt is welcome and my memory of
first using this command is that it has not-sensible defaults but I
then assumed it was designed this way because of possible use in
U-Boot scripts.

-E