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Date: Fri, 30 Sep 2005 14:42:30 +0100
From: Alex Zeffertt <ajz@cambridgebroadband.com>
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Cc: linuxppc-embedded@ozlabs.org
Subject: Re: CPM2 early console
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On Fri, 30 Sep 2005 14:22:18 +0100
Alex Zeffertt <ajz@cambridgebroadband.com> wrote:

> Till now I have worked around this problem by calling
> dcache_invalidate_range() and dcache_flush_range() before and after
> accesses to these areas.  I'm now considering changing to Kalle's
> way of doing it.
> 
> Are there any drawbacks to this approach?


To answer my own question: yes there is a drawback.

I've just done some performance tests on my driver.  In the first
test the driver uses invalidate/flush calls to keep the cache
coherent. In the second test I just use Kalle's mod to setbat().

In the second test the perfomance of the driver is roughly 1/3 of the
performance in the first test.

What I really want is a way of asserting GBL whenever the CPM accesses
ANY memory area other than DPRAM.  Hm.

Alex