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Date: Wed, 5 Sep 2007 17:23:10 -0500
From: Scott Wood <scottwood@freescale.com>
To: Dan Malek <dan@embeddedalley.com>
Subject: Re: [PATCH 1/9] 8xx: Fix CONFIG_PIN_TLB.
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On Wed, Sep 05, 2007 at 03:08:28PM -0700, Dan Malek wrote:
> All of this worked in 2.4, many changes were part
> of the evolution in 2.6...  configurable pinned entries,
> large page sizes, variations, I didn't keep track of
> all of this.  I just assumed I'd have to fix it all if I
> ever needed to use it, which I haven't.  The original
> version of 8xx could wire exactly three entries for
> 8M text, 8M data, and 8M IMMR plus upper device
> addresses.  We would set the IMMR to ff800000,
> cover the CPM, some other devices and the flash
> at the top of memory.

The IMMRs I've seen from the bootloader are ff000000 (Freescale boards)
and fa200000 (Embedded Planet).  AFAICT, the number of fixed TLB entries
is fixed at 4 on these chips, so using the fourth for flash wouldn't take
away any general-purpose TLB entries.

> >I didn't change it on a whim, I changed it because ioremap() wasn't
> >working the way it currently is.
> 
> This processor is severely resource limited.  It's
> far better to fix ioremap and take advantage of this
> performance enhancement than to further
> cripple it.  Just like other processors test for
> mapping by BATs or CAMs, the 8xx and
> probably 4xx should test for wired mapping.

I certainly agree that it would be nice to check -- my immediate goal is
to get things working, though.

-Scott