[U-Boot] [RFC] Add 'led' command

[Reinhard Meyer <u-boot@emk-elektronik.de>]

Dear Wolfgang Denk,
>> It is desired to have the led command on the BeagleBoard to allow for some
>> interaction in the scripts.
>>
>> This patch allows any board implementing the coloured LED API
>> to control the LEDs from the console.
>>
>> led [green | yellow | red | all ]  [ on | off ]
>>
>> or
>>
>> led [ 1 | 2 | 3 | all ]  [ on | off ]
>>
>> Adds configuration item CONFIG_CMD_LED enabling the command.
>>
>> Partially based on patch from Ulf Samuelsson:
>> http://www.mail-archive.com/u-boot at lists.denx.de/msg09593.html.
>>
>> Signed-off-by: Jason Kridner <jkridner@beagleboard.org>
>> ---
>>  common/Makefile  |    1 +
>>  common/cmd_led.c |  207 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 208 insertions(+), 0 deletions(-)
>>  create mode 100644 common/cmd_led.c
> 
> I understand the requirement, but I think it is more than time to come
> up with a common solution here instead of adding more and more copies
> of very similar code.
> 
> We already have:
> ...
> 	arch/arm/cpu/arm926ejs/at91/led.c
> 	board/atmel/at91cap9adk/led.c
> 	board/atmel/at91rm9200dk/led.c
> 	board/atmel/at91rm9200ek/led.c
> 	board/atmel/at91sam9260ek/led.c
> 	board/atmel/at91sam9261ek/led.c
> 	board/atmel/at91sam9263ek/led.c
> 	board/atmel/at91sam9m10g45ek/led.c
> 	board/atmel/at91sam9rlek/led.c

At least the atmel stuff are functions to implement the control of
the LEDs (via gpio, i2c, spi etc.) which inherently is board specific;
but not a command interface to control them from u-boot prompt/scripts.

His patch tries to add a command, not a LED implementation.
Such a command was on my mind for a while.

Best Regards,
Reinhard