linux-kernel - Re: [RFC] AGP initial support for chipset flushing..

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Date:	Mon, 29 Oct 2007 12:47:23 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	dri-devel@...ts.sourceforge.net
Cc:	Dave Airlie <airlied@...net.ie>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sf.net, keithp@...thp.com
Subject: Re: [RFC] AGP initial support for chipset flushing..

On Monday, October 29, 2007 1:15 am Dave Airlie wrote:
> Hi,
>
> We've uncovered a need when using the new memory manager to flush the
> chipset global write buffers on certain intel chipset due to a lack
> of coherency..
>
> The attached patches add a new AGP interface  for this purpose and
> implements this in the Intel AGP driver. This stuff is based of some
> guesswork in the 915 case from comments in the documentation :).

In this case, we're performing basically a dma_sync*(...DMA_TO_DEVICE) 
right?  Can we be sure that a single flush is sufficient?  Is there any 
window between when we flush and when we start accessing memory with 
the device that we could get into more caching trouble?

> Unfortuantely the 965 BIOS doesn't set this stuff up properly and it
> doesn't use a standard BAR address, so I have to do it by hand, I'd
> appreciate any commentary particularly in the setting up of the
> resource stuff.

Looks reasonable, I'm not sure we can do much better.  The only concern 
I have is that allocating some more PCI space like that may end up 
clobbering some *other* hidden BIOS mapping, but there's not a whole 
lot we can do about that.

Jesse
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