x86/agp: Fix agp_amd64_init regression

This fixes the regression introduced by commit
42590a75019a50012f25a962246498dead428433 ("x86/agp: Fix
agp_amd64_init and agp_amd64_cleanup").

The above commit changes agp_amd64_init() not to do anything if
gart_iommu_aperture is not zero.

If GART iommu calls agp_amd64_init(), we need to skip
agp_amd64_init() when it's called later via module_init.

The problem is that gart_iommu_init() calls agp_amd64_init()
with not zero gart_iommu_aperture so agp_amd64_init() is never
initialized.

When gart_iommu_init() calls agp_amd64_init(), agp should be
always initialized.

Reported-by: Marin Mitov <mitov@issp.bas.bg>
Reported-by: Johannes Hirte <johannes.hirte@fem.tu-ilmenau.de>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Tested-by: Marin Mitov <mitov@issp.bas.bg>
Tested-by: Kevin Winchester <kjwinchester@gmail.com>
Cc: davej@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20100125141006O.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

drivers/char/agp/amd64-agp.c

@@ -729,9 +729,6 @@ int __init agp_amd64_init(void)
 	if (agp_off)
 		return -EINVAL;
 
-	if (gart_iommu_aperture)
-		return agp_bridges_found ? 0 : -ENODEV;
-
 	err = pci_register_driver(&agp_amd64_pci_driver);
 	if (err < 0)
 		return err;
@@ -768,6 +765,14 @@ int __init agp_amd64_init(void)
 	return err;
 }
 
+static int __init agp_amd64_mod_init(void)
+{
+	if (gart_iommu_aperture)
+		return agp_bridges_found ? 0 : -ENODEV;
+
+	return agp_amd64_init();
+}
+
 static void __exit agp_amd64_cleanup(void)
 {
 	if (gart_iommu_aperture)
@@ -777,7 +782,7 @@ static void __exit agp_amd64_cleanup(void)
 	pci_unregister_driver(&agp_amd64_pci_driver);
 }
 
-module_init(agp_amd64_init);
+module_init(agp_amd64_mod_init);
 module_exit(agp_amd64_cleanup);
 
 MODULE_AUTHOR("Dave Jones <davej@redhat.com>, Andi Kleen");