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

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Date:	Sun, 27 Dec 2009 17:19:39 +0200
From:	Marin Mitov <mitov@...p.bas.bg>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [BUG] agpgart-amd64 not initialized in 2.6.33-rc2

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.

Best regards

Marin Mitov

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