MPC83xx - previous patch to set MBAR

[Kim Phillips]

On Wed, 1 Aug 2007 15:20:22 -0500
"Keith Mund" <keith.mund at clearcube.com> wrote:

> There was a u-boot 1.1.3 patch for start.S posted on the Freescale LTIB

posts concerning u-boot should go to the u-boot-users list (cc'd).

> site:
> http://www.bitshrine.org/gpp/u-boot-1.1.3-mpc83xx-cpu-4.patch
> 
> The end result simply adds a line to set MBAR to match IMMRBAR.
> 
>         lis     r3, CFG_IMMRBAR at h
>         ori     r3, r3, CFG_IMMRBAR at l
>         stw     r3, IMMRBAR(r4)
> +       mtspr   MBAR, r3
> 
> Are these patches routinely added to the mainstream u-boot code? 
> 
> Is there any reason why this fix is not a good idea?
> 
does setting MBAR really fix anything?

MBAR doesn't live up to its name.  It's a general-purpose scratch
register - the hardware doesn't do anything with it.  So, wrt integrity
within u-boot itself, I see no point/value in setting it.  If some
piece of software needs temporary storage, it can set it and use it as
it wishes, independent of u-boot.

Kim