Subject: Re: [PATCH] PowerPC: Remove hardcoded BAT configuration of IMMR in CPM early debug console

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sat, 29 May 2010 13:37:13 +1000

On Fri, 2010-05-28 at 11:18 -0500, Scott Wood wrote:
> Only the physical address should depend on where IMMR is.  We should
> use 
> fixmap instead of an arbitrary address for the effective address. 
> There's a existing FIX_EARLY_DEBUG_BASE, but it's only 128 KiB so
> we'll 
> have to either grow it, or map only a subset of IMMR.
> 
> Plus, CONFIG_PPC_EARLY_DEBUG_CPM_ADDR points to the TX descriptor,
> not 
> to the beginning of IMMR, so you should mask off the lower 20 bits
> (the 
> offset is probably less than 64K, and the BAT might just ignore the 
> extra bits anyway, but why take chances?). 

BAT has other advantages such as limiting TLB usage for things that are
used often. I think we might want to revive Grant work on early ioremap
here :-)

Cheers,
Ben.