agp/intel: Support 64-bit GMADR

Per the Intel 915G/915GV/... Chipset spec (document number 301467-005),
GMADR is a standard PCI BAR.

The PCI core reads GMADR at enumeration-time.  Use pci_bus_address()
instead of reading it again in the driver.  This works correctly for both
32-bit and 64-bit BARs.  The spec above only mentions 32-bit GMADR, but
Yinghai's patch (link below) indicates some devices have a 64-bit GMADR.

[bhelgaas: reworked starting from http://lkml.kernel.org/r/1385851238-21085-13-git-send-email-yinghai@kernel.org]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/char/agp/intel-agp.h

@@ -55,7 +55,7 @@
 #define INTEL_I860_ERRSTS	0xc8
 
 /* Intel i810 registers */
-#define I810_GMADDR		0x10
+#define I810_GMADR_BAR		0
 #define I810_MMADDR		0x14
 #define I810_PTE_BASE		0x10000
 #define I810_PTE_MAIN_UNCACHED	0x00000000
@@ -113,7 +113,7 @@
 #define INTEL_I850_ERRSTS	0xc8
 
 /* intel 915G registers */
-#define I915_GMADDR	0x18
+#define I915_GMADR_BAR	2
 #define I915_MMADDR	0x10
 #define I915_PTEADDR	0x1C
 #define I915_GMCH_GMS_STOLEN_48M	(0x6 << 4)

drivers/char/agp/intel-gtt.c

@@ -608,9 +608,8 @@ static bool intel_gtt_can_wc(void)
 
 static int intel_gtt_init(void)
 {
-	u32 gma_addr;
 	u32 gtt_map_size;
-	int ret;
+	int ret, bar;
 
 	ret = intel_private.driver->setup();
 	if (ret != 0)
@@ -660,14 +659,11 @@ static int intel_gtt_init(void)
 	}
 
 	if (INTEL_GTT_GEN <= 2)
-		pci_read_config_dword(intel_private.pcidev, I810_GMADDR,
-				      &gma_addr);
+		bar = I810_GMADR_BAR;
 	else
-		pci_read_config_dword(intel_private.pcidev, I915_GMADDR,
-				      &gma_addr);
-
-	intel_private.gma_bus_addr = (gma_addr & PCI_BASE_ADDRESS_MEM_MASK);
+		bar = I915_GMADR_BAR;
 
+	intel_private.gma_bus_addr = pci_bus_address(intel_private.pcidev, bar);
 	return 0;
 }