netdev - Re: [PATCH 002/002] de2104x: support for systems lacking cache coherence

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Date:	Sun, 08 Feb 2009 23:45:02 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	risto.suominen@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 002/002] de2104x: support for systems lacking cache
 coherence

From: Risto Suominen <risto.suominen@...il.com>
Date: Mon, 9 Feb 2009 09:27:49 +0200

> Add a configurable Descriptor Skip Length for systems that lack cache coherence.
> 
> Signed-off-by: Risto Suominen <Risto.Suominen@...il.com>

I really don't see why this patch could possibly be necessary.

On systems that lack cache coherence:

1) {pci,dma}_alloc_{consistent,coherent}() give kernel mappings of
   the buffer with the cache disabled.  Therefore the device and
   and cpu see the correct data.

2) {pci,dma}_{map,unmap}_{single,sg}() do the appropriate cache
   flushing.

   Explicit syncing between cpu and device can be performed
   using {pci,dma}_sync_{single,sg}() as needed.

Therefore, this patch is superfluous.
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