linux-kernel - Re: Question about iommu on x86

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Message-ID: <21491fcfb013e21177140326efc0ee66@admin.gogi.tv>
Date:	Wed, 01 Jun 2011 17:10:44 +0100
From:	Daniel Haid <d.haid@...i.tv>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	<linux-kernel@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>
Subject: Re: Question about iommu on x86_64 and radeon driver.

> Look in the source code. I somehow assumed it would activate it
> but maybe it isn't. And the problem you have is related to
> something else?

 If I have read the code correctly the only way to get
 swiotlb_force=1 in lib/swiotlb.c is to add the "swiotlb=force"
 argument to the kernel parameters.

 Without it on VIA chipsets swiotlb gets activated, but with
 swiotlb_force=0. In this case DMA to addresses below 4GB should be
 direct.

 But since I still get the error the radeon driver must (incorrectly)
 allocate memory above 4GB somewhere, but where?

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