linux-kernel - Re: [BUG] agpgart-amd64 not initialized in 2.6.33-rc2

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Message-ID: <20091228081021.GD28652@elte.hu>
Date:	Mon, 28 Dec 2009 09:10:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Marin Mitov <mitov@...p.bas.bg>, Dave Jones <davej@...hat.com>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com
Subject: Re: [BUG] agpgart-amd64 not initialized in 2.6.33-rc2


* Marin Mitov <mitov@...p.bas.bg> wrote:

> On Monday 28 December 2009 08:37:33 am FUJITA Tomonori wrote:
> > On Sun, 27 Dec 2009 17:19:39 +0200
> > Marin Mitov <mitov@...p.bas.bg> wrote:
> > 
> > > Hi all,
> > > 
> > > Recently (2.6.33-rc2 kernel, x86_64, 4GB RAM) I found (in dmesg):
> > > 
> > > [drm:mga_do_agp_dma_bootstrap] *ERROR* Unable to acquire AGP: -19
> > > 
> > > and there is no /dev/agpgart device on the machine while all is OK 
> > > if booting 2.6.32.2. 
> > > 
> > > In both kernels I have:
> > > 
> > > CONFIG_AGP=y
> > > CONFIG_AGP_AMD64=y
> > > 
> > > CONFIG_GART_IOMMU=y
> > > 
> > > but nevertheless dmesg shows:
> > > 
> > > PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> > > 
> > > due to quirks in via K8T800Pro host bridge.
> > > 
> > > Looking for the reason I found that agp_amd64_init() appears in:
> > > 
> > > #ifndef CONFIG_GART_IOMMU
> > > module_init(agp_amd64_init);
> > > module_exit(agp_amd64_cleanup);
> > > #endif
> > > 
> > >  /*  so it is not invoked here due to CONFIG_GART_IOMMU=y   */
> > > 
> > > and also appears in:
> > >  
> > > arch/x86/kernel/pci-gart_64.c, function: gart_iommu_init()
> > > 
> > > The last one is part of the struct x86_init_ops(struct x86_init_iommu, as a function pointer) 
> > > only if gart-iommu is successfully detected, which is not the case here due to the quirk, 
> > > so agp_amd64_init() is not invoked here neither. 
> > > 
> > > Sure, configuring the kernel without CONFIG_GART_IOMMU=y (which is not user selectable)
> > > 
> > > should solve the problem, but usually users do not know about quirks, so it should
> > > work even as set here (and it works up to 2.6.32.2). I believe the bug is introduced
> > > with the changes in the order iommu detect/init works for 2.6.33.
> > > 
> > > I am here for additional info/tests.
> > 
> > Sorry about the regression. Does this works?
> 
> Yes, it works for me, thank you.

Great! Fujita-san, mind sending a fully changelogged version of the patch with 
Tested-by and your Signed-off-by?

Dave, do you want to push this fix to Linus, or should we do it via 
x86/urgent?

Thanks,

	Ingo
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