linux-kernel - Re: IOMMU and graphics cards

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Date:	Fri, 8 May 2009 11:35:27 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	David Miller <davem@...emloft.net>
Cc:	dwmw2@...radead.org, airlied@...ux.ie,
	linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp,
	iommu@...ts.linux-foundation.org, mingo@...hat.com
Subject: Re: IOMMU and graphics cards

On Thu, May 07, 2009 at 11:36:32AM -0700, David Miller wrote:
> From: David Woodhouse <dwmw2@...radead.org>
> Date: Thu, 07 May 2009 11:22:01 +0100
> 
> > On Thu, 2009-05-07 at 12:01 +0200, Joerg Roedel wrote:
> >> > Looks like the DRM code uses the DMA API.
> >> 
> >> The proprietary drivers make problems so far. For the ATI one I am in
> >> contact with the developers to try to fix it. But I can't do anything
> >> about the other proprietary driver I am aware of :-(
> > 
> > I see no harm in "breaking" code which was already broken. If that's the
> > only reason we're enabling the graphics workaround, let's turn it off.
> 
> Seriously, this is an enormous price to pay just for one bad apple
> proprietary driver.
> 
> I can't believe the level of concessions some people are suggesting.

This concession is already in the VT-d code. And this concession is
_enabled_ in enterprise distribtions supporting VT-d. I don't like the
way it is implemented there and I definitly will not implement a similar
way for the AMD IOMMU. What I try to achieve is a consistent solution
for both IOMMUs. Having the broken drivers work on VT-d but not on
AMD IOMMU is clearly a bad solution.

The other way to achieve consistency is to remove the workaround from
VT-d code which significantly increases the chance to get the broken
stuff fixed. David?

> Let's not make IOMMU's basically useless by working around one broken
> driver.

Agreed.

> Proper interfaces for what this driver is trying to do have existed in
> the kernel for 10+ years.  There are no excuses, and it's time for
> Nvidia to get with the game plan.

Agreed.

Joerg

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