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

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Date:	Mon, 28 Dec 2009 15:37:33 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mitov@...p.bas.bg
Cc:	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

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?

Thanks,

diff --git a/drivers/char/agp/amd64-agp.c b/drivers/char/agp/amd64-agp.c
index 2fb2e6c..5aa7a58 100644
--- a/drivers/char/agp/amd64-agp.c
+++ b/drivers/char/agp/amd64-agp.c
@@ -725,9 +725,14 @@ static struct pci_driver agp_amd64_pci_driver = {
 int __init agp_amd64_init(void)
 {
 	int err = 0;
+	static int done = 0;
 
 	if (agp_off)
 		return -EINVAL;
+
+	if (done++)
+		return agp_bridges_found ? 0 : -ENODEV;
+
 	err = pci_register_driver(&agp_amd64_pci_driver);
 	if (err < 0)
 		return err;
@@ -771,12 +776,8 @@ static void __exit agp_amd64_cleanup(void)
 	pci_unregister_driver(&agp_amd64_pci_driver);
 }
 
-/* On AMD64 the PCI driver needs to initialize this driver early
-   for the IOMMU, so it has to be called via a backdoor. */
-#ifndef CONFIG_GART_IOMMU
 module_init(agp_amd64_init);
 module_exit(agp_amd64_cleanup);
-#endif
 
 MODULE_AUTHOR("Dave Jones <davej@...hat.com>, Andi Kleen");
 module_param(agp_try_unsupported, bool, 0);
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