[WORKAROUND] modular AGP/ disabled IOMMU in 2.6.18 on amd64

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

I don't find a way to disable IOMMU in the new 2.6.18-r2 kernel on amd64 platform.

As I see, the old CONFIG_GART_IOMMU option is split into CONFIG_IOMMU and CONFIG_CALGARY_IOMMU.
menuconfig gives a handle for CONFIG_CALGARY_IOMMU but not for CONFIG_IOMMU which is always set.

Is this by design or a bug ?

Since CONFIG_IOMMU is set, kernel based AGP is forced, and, say, nvidia AGP can't be used.
My problem is however different. On my quad-opteron headless server I found (over a year ago) that without IOMMU=off and AGP=off
(there is no AGP bus at all on it) I expereienced some instabilities, so I'm a bit scared to have it enabled.

IanPo · Posted: Mon Nov 20, 2006 8:45 am Post subject:

my kernel is 2.6.18-r2, too.
I tried to set the option mentioned off manually in .config as well (was fighting with ati-drivers; according to the guide CONFIG_GART_IOMMU was to be set to "n").
Having "make" started i read something about "writing in .config" in console output.
I stopped compilation and peeped into .config - the option CONFIG_IOMMU was "y" again.
So i could've set option CALGARY_IOMMU but CONFIG_IOMMU.
My opinion: it's not a bug, it's a new feature.
In older kernels it was different: http://gentoo-wiki.com/HOWTO_ATI_on_amd64
Here's some explanations about IOMMU: http://www.linuxhq.com/kernel/v2.6/18-rc2/arch/x86_64/Kconfig

nationdemon · n00b Joined: 15 Nov 2006 Posts: 30 Location: Dresden

Got the same prob on my girls amd64 the only one with such a god damned ati... sorry but these cards are annoying. It took me 3 days to get it running with glx and than after a month without probs the new kernel hits ground. I've found the header files of both recommended modules (agpgart and amd64-agp)... If I step back to 2.6.17-r8 Iam able to start X with real good results on glxgears and fgl_glxgears (and ati instead of mesa in glxinfo) after reinstalling ati-drivers. But with 2.6.18-r2 nothing works

I've tried to edit the .config setting the options to m and funny it is still m but neither agpgart nor amd64-agp had been installed.

ps.: plz excuse my worse english

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

IanPo · Posted: Mon Nov 20, 2006 8:55 pm Post subject:

nationdemon · n00b Joined: 15 Nov 2006 Posts: 30 Location: Dresden

@ dmpogo THX, it works again... Such an easy solution :oops:

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

To summarize the workaround for those who wants/needs the ability for in-kernel AGP to be disabled or compiled as a module and/or IOMMU disabled on AMD64 under 2.6.18 kernels

In /usr/src/linux-2.6.18-gentoo-r2/arch/x86_64/Kconfig replace the line 406

IanPo · Posted: Tue Nov 21, 2006 7:37 am Post subject:

Blimey, i was doing it wrong! Value "n" is illegal in .config, should've used "is not set" instead. Those "y"s and "m"s led me the wrong way. :oops:

No matter if you deleting "if EMBEDDED" as written above, just for the record.

IanPo · Posted: Tue Nov 21, 2006 6:31 pm Post subject:

Now testing.

Before:

.config

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

IanPo,

There is one fine point. I don't know if it makes sense (or even can cause problems) to have CALGARY_IOMMU enabled while IOMMU disabled.
Kconfig does not condition CONFIG_CALGARY_IOMMU to be dependent on CONFIG_IOMMU, but this may be because they thought that IOMMU is forced anyway !

So I would be disabling CALGARY every time I disable IOMMU just in case. As you did, of course

IanPo · Posted: Wed Nov 22, 2006 12:40 pm Post subject:

I agree. For we're tweaking the option manually we also have to set all the dependent ones in accordance.

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

Aitikin · Apprentice Joined: 14 May 2005 Posts: 227

I've tried this fix myself and I can't get it to work. My make menuconfig still does not have the IOMMU option available or the agpgart option available. I wish I knew what was goingg wrong. I'm going to try putting the default to N and see what that does.
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dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

IanPo · Posted: Sun Dec 03, 2006 7:59 pm Post subject:

eNTi · Posted: Thu Dec 07, 2006 8:19 am Post subject:

sorry to ask a little offtopic here, but isn't there a reason, why it's forced into the kernel? can one really use NvAGP on amd64? if yes, that would solve my suspend2 issues, i think.
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dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3511 Location: Canada

Stolz · Posted: Tue Dec 19, 2006 4:44 pm Post subject:

Thanks for the workaround, dmpogo. I have an AMD64 with nVidia proprietary drivers. Since 2.6.18, as soon as I start X, the system starts randomly stalling/freezing, the hard disk light stays lit, and X performance becomes crappy. Disabling IOMMU with the workaround enables again Nvidia's AGP and solves the problem

eNTi · Posted: Wed Dec 20, 2006 11:50 am Post subject:

yeah it's good, to know, that there is something you can do, to use nvagp after all, but i wouldn't recommend it to any gamers out there. it's very slow on my machine.
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jonnevers · Posted: Sat Dec 23, 2006 4:21 pm Post subject:

thanks!

I tried everything to get my system to use a kernel > 2.6.17. removing 'if embedded' and then disabling IOMMU and the kernel's AGPART in 'make menuconfig' worked like a charm.

AMD64 xorg-x11 7.1, nvidia-drivers 9742, and beyond-sources 2.6.19-beyond2, fully working!

Decibels · Veteran Joined: 16 Aug 2002 Posts: 1630 Location: U.S.A.

Yes, thanks. I have always had to disable IOMMU on my amd64 to get video to work with nvidia driver. I really dislike the fact they made it embedded and not allow us the option to disable it.

I had some trouble with grub and splashutils on 2.6.18-gentoo-r2 kernel so couldn't boot. Ends up that was grub, didn't like some command always had in there for others, but just get black screen when kernel loading. So thought that had to do with the IOMMU thing. Tried the 'nv' driver to get past it, but since figured out it was grub haven't retried with IOMMU enabled and 'nv' driver since removed the embedded.

Once I got past the grub problem, would boot up fine until starting X. Then nothing. That is when removed the embedded on the IOMMU and just incase agpgart was screwed up made it modular so could use the nvagp if needed to try. BUT NO, once disabled IOMMU everything worked fine. Left agpgart as a module and didn't have to try the nvagp. IOMMU is what screwed up the whole process and it appears the kernel maintainers are not going to change it because people were choosing Y when meant N,...
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Decibels · Veteran Joined: 16 Aug 2002 Posts: 1630 Location: U.S.A.

I went back and left IOMMU enabled (embedded) and tried variouse iommu kernel options. It still appears that disabling by changing Kconfig is the best option.

passing:
iommu=off doesn't work. Still no X with nvidia binary.
Also tried size, allowed, noforce, noagp, iommu=memaper=1 & 2 couldn't get X with nvidia binary.
Only one that works is iommu=noaperture.
Then checked dmesg to see and still get aperture:

Decibels · Veteran Joined: 16 Aug 2002 Posts: 1630 Location: U.S.A.

Found out that if you have bios agp aperture set to 32Mb that the kernel will:

Shiznitz · Posted: Sat Jan 06, 2007 4:55 pm Post subject:

Would this be the only workaround you guys can find? It seems as if my Motherboard's BIOS does not let me edit the AGP aperture.

Shiznitz