[U-Boot] i.MX6: mx6qsabrelite: allow use with Freescale 2.6.38 kernels

[Dirk Behme <dirk.behme@googlemail.com>]

Dear Wolfgang,

On 03.03.2012 10:38, Wolfgang Denk wrote:
> Dear Dirk,
>
> In message<4F51BBA9.4090608@googlemail.com>  you wrote:
>>
>> Having Freescale working on these quite old and unclean U-Boot and
>> Kernel versions is a pain. Kernel is an other topic, but with U-Boot,
>> thanks to the very good work of everybody, we are in a good position
>> to get rid of the old Freescale U-Boot, now. And get everybody to work
>> with mainline and create patches against it.
>
> ACK.
>
>> So if it helps to apply some backward compatibility to make it easier
>> for everybody, esp. Freescale, to switch to mainline U-Boot, I think
>> we should try it.
>
> Agreed.  If these patches were only for backward compatibility I would
> not complain much.  But they are known to introduce forward incompati-
> bilities with all this MACH_ID stuff, and this is what I would like to
> avoid.

Now I'm just trying to learn something regarding [1]:

Which changes would you accept in the category 'backward compatibility'?

And which changes 'introduce forward incompatibilities', and what are 
these incompatibilities?

Many thanks and best regards

Dirk

[1]

http://lists.denx.de/pipermail/u-boot/2012-March/119207.html

http://lists.denx.de/pipermail/u-boot/2012-March/119208.html

(assuming this will be changed to

--- a/include/configs/mx6qsabrelite.h
+++ b/include/configs/mx6qsabrelite.h
@@ -27,6 +27,7 @@
  #define CONFIG_SYS_MX6_CLK32           32768
  #define CONFIG_DISPLAY_CPUINFO
  #define CONFIG_DISPLAY_BOARDINFO
+#define CONFIG_MACH_TYPE       3769

  #include <asm/arch/imx-regs.h>

)