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

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Message-Id: <20091125085730S.fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 25 Nov 2009 08:57:43 +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 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.
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