linux-kernel - Re: [Intel-gfx] [PATCH] intel-gtt: fix memory corruption with GM965 and >4GB RAM

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Date:	Mon, 28 Feb 2011 14:46:35 +0800
From:	Zhenyu Wang <zhenyuw@...ux.intel.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Jan Niehusmann <jan@...dor.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH] intel-gtt: fix memory corruption with
 GM965 and >4GB RAM

On 2011.02.26 00:05:27 +0100, Daniel Vetter wrote:
> On Fri, Feb 25, 2011 at 10:18:16PM +0000, Chris Wilson wrote:
> > So, I'm happy to use your patch to workaround the known erratum. I just
> > wish I had an explanation as to what is actually causing the corruption.
> > What I want to make sure is that we don't paper over a real bug by
> > thinking it is yet another silicon issue.
> 
> Actually, on style points I prefer your patch: The hw status page is
> allocated with drm_pci_alloc which calls dma_alloc_coherent, so setting
> the coherent mask is sufficient. The dma mask set in the gtt is
> essentially useless, because we call get_user_pages on everything anyway
> (in gem - iirc agp uses it). I just think it's confusing to limit the
> general dma mask and continue to happily map pages above 4G.
> 

Think about IOMMU engine, we need to set dma_mask properly for
returned dma mapping address be limited in max range that can be
handled in GTT entry. 

-- 
Open Source Technology Center, Intel ltd.

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