linux-kernel - Re: [PATCH] x86: fix gart iommu using for amd 64 bit system

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Message-Id: <20091125165601R.fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 25 Nov 2009 16:56:32 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mingo@...e.hu
Cc:	fujita.tomonori@....ntt.co.jp, yinghai@...nel.org, hpa@...or.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix gart iommu using for amd 64 bit system

On Wed, 25 Nov 2009 08:25:04 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
> 
> > On Tue, 24 Nov 2009 16:26:45 +0100
> > Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > 
> > > * FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
> > > 
> > > > > don't think user will like to use SWIOTLB instead of swiotlb.
> > > > 
> > > > I doubt that users care about a way to fix their problems.
> > > 
> > > As far as swiotlb vs. GART goes, arguably a non-bouncing hw based 
> > > solution (GART) is superior to a bouncing one (swiotlb), right?
> > 
> > Yeah, but GART is not a real IOMMU that always does address 
> > translation. If users want performance, they need 64bit DMA capable 
> > devices to skip GART. With such devices, GART and SWIOTLB are same.
> > 
> > So this hacky GART workaround is useful for only people who use non 
> > 64bit DMA devices and broken BIOS with GART. IMO, it's not worth 
> > having the workaround.
> 
> Well, what Yinghai is saying that for that (nonzero) subset of people 
> this change is a regression, and his patch fixes that. We dont do 
> regressions so this needs to be addressed.

OK, I guess that I have to wait until nobody cares about GART.

Anyway, my patch fixes his issue without any regression:

http://marc.info/?l=linux-kernel&m=125907069703595&w=2

I'll post the second version of it after you merge the following fix:

http://marc.info/?l=linux-kernel&m=125910650500523&w=2


Thanks,
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