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

[Wolfgang Denk]

Dear Dirk Behme,

In message <4F52015A.2080003 at googlemail.com> you wrote:
> 
> > 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'?

There are 3 commits in this series:

[PATCH 1/3] i.MX6: mx6qsabrelite: add CONFIG_REVISION_TAG
[PATCH 2/3] i.MX6: mx6qsabrelite: add MACH_TYPE_MX6Q_SABRELITE
[PATCH 3/3] i.MX6: mx6qsabrelite: add ext2 support

I dislike #1 because it uses the completely undocumented
CONFIG_REVISION_TAG, and I agree with Marek's and Stefano's comments.

The problems I mentioned are with # 2, which now would depend on
MACH_TYPE_MX6Q_SABRELITE, which may or may not exist.

Also, I think we should not need this any more at all, as we now have
DT support in Linux on ARM, too.

I see no issues with # 3.

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

See the recent problems that occurred when RMK decided to "clean up"
the machids file.

> (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

Such a change would avoid breakages as the ones mentioned above, but
is this nice?  Either we have a mach-types.h that can be used, or we
don't, in which case we should stop using any definitions from it,
especially for new boards where it's not needed due to DT support in
the kernel.

Best regards,

Wolfgang Denk

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