drm/i915/gen8: Flip the 48b switch

Use 48b addresses if hw supports it (i915.enable_ppgtt=3).
Update the sanitize_enable_ppgtt for 48 bit PPGTT mode.

Note, aliasing PPGTT remains 32b only.

v2: s/full_64b/full_48b/. (Akash)
v3: Add sanitize_enable_ppgtt changes until here. (Akash)
v4: Update param description (Chris)

Cc: Akash Goel <akash.goel@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -104,9 +104,11 @@ static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
 {
 	bool has_aliasing_ppgtt;
 	bool has_full_ppgtt;
+	bool has_full_48bit_ppgtt;
 
 	has_aliasing_ppgtt = INTEL_INFO(dev)->gen >= 6;
 	has_full_ppgtt = INTEL_INFO(dev)->gen >= 7;
+	has_full_48bit_ppgtt = IS_BROADWELL(dev) || INTEL_INFO(dev)->gen >= 9;
 
 	if (intel_vgpu_active(dev))
 		has_full_ppgtt = false; /* emulation is too hard */
@@ -125,6 +127,9 @@ static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
 	if (enable_ppgtt == 2 && has_full_ppgtt)
 		return 2;
 
+	if (enable_ppgtt == 3 && has_full_48bit_ppgtt)
+		return 3;
+
 #ifdef CONFIG_INTEL_IOMMU
 	/* Disable ppgtt on SNB if VT-d is on. */
 	if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped) {
@@ -141,7 +146,7 @@ static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
 	}
 
 	if (INTEL_INFO(dev)->gen >= 8 && i915.enable_execlists)
-		return 2;
+		return has_full_48bit_ppgtt ? 3 : 2;
 	else
 		return has_aliasing_ppgtt ? 1 : 0;
 }

drivers/gpu/drm/i915/i915_params.c

@@ -111,7 +111,7 @@ MODULE_PARM_DESC(enable_hangcheck,
 module_param_named_unsafe(enable_ppgtt, i915.enable_ppgtt, int, 0400);
 MODULE_PARM_DESC(enable_ppgtt,
 	"Override PPGTT usage. "
-	"(-1=auto [default], 0=disabled, 1=aliasing, 2=full)");
+	"(-1=auto [default], 0=disabled, 1=aliasing, 2=full, 3=full with extended address space)");
 
 module_param_named_unsafe(enable_execlists, i915.enable_execlists, int, 0400);
 MODULE_PARM_DESC(enable_execlists,