[U-Boot] subcmd handling

[Frans Meulenbroeks]

It was hinted (iirc by Detlev) that I'd have a stab at subcmd handling
(at least for i2c).
As example bootm was suggested.
I've peeked at the bootm code and the code in command.c.
It seems bootm has some internal state engine, that is somewhat less
applicable for other commands.

My proposal for i2c:

have an array
static cmd_tbl_t cmd_i2c_sub[] = { };
whiich is populated/initialized  by U_BOOT_CMD_MKENT macro invocations
for the various subcommands.

The function do_i2c which now handles the subcmd parsing changes into:

int do_i2c(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
{
     cmd_tbl_t *c;

        /* Strip off leading 'i2c' command argument */
        argc--;
        argv++;

        c = find_cmd_tbl(argv[0], &cmd_i2c_sub[0], ARRAY_SIZE(cmd_i2c_sub));

    if (c) {
       return  c->cmd(cmdtp, flag, argc, argv);
    }
    else
   {
           cmd_usage(cmdtp);
           return 0;

    }
}

(and sorry for the messy layout)

A few questions before I actually implement and test this:

any comments on this proposal ?

What should be the return value in case the usage is printed? do_i2c
returns 0 in that case
however do_bootm_subcommand returns 1 in that case.

We might also consider putting the help texts in  U_BOOT_CMD_MKENT.
Then U_BOOT_CMD should probably be aware of the child commands and
should use the help of the child commands to print its help.

The first entry in  U_BOOT_CMD_MKENT is the name. This is stringified
by using a # in the macro.
Personally I would like to change it and have string quotes in the
macro invocation so that it is immediately visible when reading the
code that it is a string, not e.g. a variable.
E.g. we would get
 U_BOOT_CMD_MKENT("start", ...
instead of
 U_BOOT_CMD_MKENT(start, ...
what we have now where for the casual reader not up to date on the
definition of the macro it  might look as if a var is passed.
(btw passing a string could also allow for passing an empty string,
which could be used to add non-command assoicated help texts).

As I have no plans to implement this more than once,  I would
appreciate feedback before starting to actually code it.

Frans.