[U-Boot] [RFC]: always relocate u-boot before the framebuffer

[Wolfgang Denk]

Dear Tom,

In message <20130102154854.GC14738 at bill-the-cat> you wrote:
> 
> > Please see my responses.  This is definitely NOT a good idea, it will
> > break most (all?) boards that use CONFIG_FB_ADDR in the way it was
> > intended for.
> 
> I think this means we've got people not understanding what the variable
> IS for.  And at the high level, the idea of "lets transition from U-Boot
> to Linux without a flicker" is good.  So, what is the variables we
> should be using for this, today?  Or do we need to add and document
> more?  Or are we all just failing to RTFM here?

I think the key problem is insufficient documentation of what
CONFIG_FB_ADDR is intended for (i. e. graphics controllers with
external video RAM).  Eventualy a patch as attached might help?

The idea of "lets transition from U-Boot to Linux without a flicker"
is as old as PPCBoot (i. e. even predates U-Boot).  The standard
mechanism as implemented should work out of the box, assuming that
both U-Boot and Linux use the same configuration of the graphics
controller (resulting in the same size of the needed frame buffer
memory).  And if they use different configurations, you won't be able
to pass a pre-initialized frame buffer ayway.

The problem Jeroen ran into is/was caused by the fct that U-Boot and
Linux computed different sizes for the frame buffer.  I think this is
either a bug, or a difference in the configuration, but Jeroen did not
reply to my question for the reason for this difference yet.

Best regards,

Wolfgang Denk

Suggested doc patch: