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Au1500 hardware cache coherency

To: Pete Popov <ppopov@mvista.com>, Linux MIPS mailing list <linux-mips@linux-mips.org>
Subject: Au1500 hardware cache coherency
From: Hartvig Ekner <hartvig@ekner.info>
Date: Mon, 31 Mar 2003 14:08:24 +0200
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Hi Pete,

I am attempting to use the HW coherency feature of the AU1500 to avoid SW 
flushes and increase the performance.
In the config-shared.in file, I can see that the CONFIG_NONCOHERENT_IO define 
is always set for the AMD
eval boards, which results in SW cache flushes when dma_cache_xxx functions are 
called. If HW coherency is
working, this define should not be set.

However, in your drivers, you only call the dma_cache functions from 
au1000/common/usbdev.c, but not from e.g. the ethernet
driver or the audio driver. Is this intentional? It seems that the ethernet & 
audio driver already relies on HW
coherency to function correctly (and it also sets the MAC enable bits 
accordingly, to force all ETH DMA
accesses to be coherent), so why not USB also?

When turning off NONCOHERENT_IO, there are some bugs (not in AU1000 code) which 
prevents the code from
compiling, but I have fixed these. And the kernel boots, but during some large 
disk-copy tests, I get occasional
data errors which I'm looking in to.

So before spending more time on debugging this, and creating patches for using 
HW coherency, I wanted to hear
your input - maybe there are known problems in the Au1500 coherency 
implementation?

/Hartvig



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