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

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Date:	Mon, 29 Oct 2007 13:12:45 -0700
From:	Jesse Barnes <jesse.barnes@...el.com>
To:	Dave Airlie <airlied@...ux.ie>
Cc:	dri-devel@...ts.sourceforge.net, keithp@...thp.com,
	linux-kernel@...r.kernel.org, dri-devel@...ts.sf.net
Subject: Re: [RFC] AGP initial support for chipset flushing..

On Monday, October 29, 2007 12:52 pm Dave Airlie wrote:
> > 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?
>
> Not that I can think off, but I don't work for the company who
> screwed up the coherency :-), and I don't have the docs, so please
> investigate for me ;-)

It *looks* like it'll be enough.  I assume Keith has talked to the 
chipset guys to confirm this.

> > 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.
>
> Again I'm trying to workaround broken BIOS.. nothing I can do.

Right, BIOSes are so much fun to deal with.  One other thing:  it looks 
like the flush mmio space has to be allocated above the top of DRAM but 
below 4G.  I wonder if there's an easy way to guarantee this with the 
pci_bus* routines...

Jesse
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