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

[Caleb Connolly]

Hi,

On 31/08/2024 23:22, E Shattow wrote:
> 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.

I'm not sure what the rule is about breaking changes in the CLI, I do 
think this is not a realistic concern here though. Maybe Tom or Simon 
can weigh in?
> 
> 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.

Since I call set_working_fdt_addr() it prints a message telling you that 
the fdt address was set on the first call.
> 
> 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.

Thanks.
> 
> -E

-- 
// Caleb (they/them)