Re: Question about iommu on x86_64 and radeon driver.

[Daniel Haid]

> There had to be more than 'Map around memory hole'? Was it called
> GART or IOMMU?
I do not think that there was "IOMMU" or "GART" written there,
but I do not think that the mainboard in question has an IOMMU
(Am I correct that it would be a feature of the mainboard while
the AMD GART is a feature of the CPU?).
I will look again as soon as I have physical access to the system.

> The problem you are hitting (I think) is that the AMD GART poor-man
> IOMMU is turned off
> and the SWIOTLB is used instead. If you would like some technical
> details, take a look at:
>
> http://lists.freedesktop.org/archives/dri-devel/2011-January/006885.html
> (the point #2 is what you are hitting).

You are correct. In all the cases where the radeon card does not work
I see that SWIOTLB has been enabled in the kernel log.

So this is a bug? I suppose that all hardware should be working with
SWIOTLB? Will a patch that fixes this somewhen be included?
(The bug where your link points to was closed with WONTFIX)

> Not sure why the AMD GART IOMMU gets disabled on VIA chipsets. You 
> might
> want to use 'git gui blame arch/x86/kernel/early-quirks.c' and look
> at the code in question to figure that out.
> Well, if everything works.... but you might just want to use
> the git gui blame to take a look at the back-story of why the quirk
> was added.

Unfortunately I am getting crashes with "iommu=allowed". I will look
at git blame.

Thank you for your answers.

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