drm/i915: Use Graphics Base of Stolen Memory on all gen3+

So I made the mistake of missing that the desktop and mobile chipsets
have different layouts in their PCI configurations, and we were
incorrectly setting the wrong physical address for stolen memory on
mobile chipsets.

Since all gen3+ are actually consistent in the location of the GBSM
register in the PCI configuration space on device 2 (the GPU), use it.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: Drop cc: stable and fudge conflicts.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -45,45 +45,27 @@
 static unsigned long i915_stolen_to_physical(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct pci_dev *pdev = dev_priv->bridge_dev;
 	struct resource *r;
 	u32 base;
 
-	/* On the machines I have tested the Graphics Base of Stolen Memory
-	 * is unreliable, so on those compute the base by subtracting the
-	 * stolen memory from the Top of Low Usable DRAM which is where the
-	 * BIOS places the graphics stolen memory.
+	/* Almost universally we can find the Graphics Base of Stolen Memory
+	 * at offset 0x5c in the igfx configuration space. On a few (desktop)
+	 * machines this is also mirrored in the bridge device at different
+	 * locations, or in the MCHBAR. On gen2, the layout is again slightly
+	 * different with the Graphics Segment immediately following Top of
+	 * Memory (or Top of Usable DRAM). Note it appears that TOUD is only
+	 * reported by 865g, so we just use the top of memory as determined
+	 * by the e820 probe.
 	 *
-	 * On gen2, the layout is slightly different with the Graphics Segment
-	 * immediately following Top of Memory (or Top of Usable DRAM). Note
-	 * it appears that TOUD is only reported by 865g, so we just use the
-	 * top of memory as determined by the e820 probe.
-	 *
-	 * XXX gen2 requires an unavailable symbol and 945gm fails with
-	 * its value of TOLUD.
+	 * XXX However gen2 requires an unavailable symbol.
 	 */
 	base = 0;
-	if (IS_VALLEYVIEW(dev)) {
+	if (INTEL_INFO(dev)->gen >= 3) {
+		/* Read Graphics Base of Stolen Memory directly */
 		pci_read_config_dword(dev->pdev, 0x5c, &base);
 		base &= ~((1<<20) - 1);
-	} else if (INTEL_INFO(dev)->gen >= 6) {
-		/* Read Base Data of Stolen Memory Register (BDSM) directly.
-		 * Note that there is also a MCHBAR miror at 0x1080c0 or
-		 * we could use device 2:0x5c instead.
-		*/
-		pci_read_config_dword(pdev, 0xB0, &base);
-		base &= ~4095; /* lower bits used for locking register */
-	} else if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
-		/* Read Graphics Base of Stolen Memory directly */
-		pci_read_config_dword(pdev, 0xA4, &base);
+	} else { /* GEN2 */
 #if 0
-	} else if (IS_GEN3(dev)) {
-		u8 val;
-		/* Stolen is immediately below Top of Low Usable DRAM */
-		pci_read_config_byte(pdev, 0x9c, &val);
-		base = val >> 3 << 27;
-		base -= dev_priv->mm.gtt->stolen_size;
-	} else {
 		/* Stolen is immediately above Top of Memory */
 		base = max_low_pfn_mapped << PAGE_SHIFT;
 #endif