drm/i915: Sanitize the enable_ppgtt module option once

Otherwise we'll end up spamming dmesg on every context creation on snb
with vt-d enabled. This regression was introduced in

commit 246cbfb5
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Fri Dec 6 14:11:14 2013 -0800

    drm/i915: Reorganize intel_enable_ppgtt

As the i915.enable_ppgtt is read-only it cannot be changed after the
module is loaded and so we can perform an early sanitization of the
values.

v2:
- Add comment and pimp commit message (Chris)
- Use the param consistently (Jani)

v3:
- Fix init sequence on pre-gen6 by moving the sanitize_ppgtt call to
  gtt_init. Fixes boot hangs on pre-gen6.
- Add a debug output for the sanitize ppgtt mode.

References: https://lkml.org/lkml/2014/4/17/599
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77916
Cc: Alessandro Suardi <alessandro.suardi@gmail.com>
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -34,25 +34,35 @@ static void gen8_setup_private_ppat(struct drm_i915_private *dev_priv);
 
 bool intel_enable_ppgtt(struct drm_device *dev, bool full)
 {
-	if (i915.enable_ppgtt == 0 || !HAS_ALIASING_PPGTT(dev))
+	if (i915.enable_ppgtt == 0)
 		return false;
 
 	if (i915.enable_ppgtt == 1 && full)
 		return false;
 
+	return true;
+}
+
+static int sanitize_enable_ppgtt(struct drm_device *dev, int enable_ppgtt)
+{
+	if (enable_ppgtt == 0 || !HAS_ALIASING_PPGTT(dev))
+		return 0;
+
+	if (enable_ppgtt == 1)
+		return 1;
+
+	if (enable_ppgtt == 2 && HAS_PPGTT(dev))
+		return 2;
+
 #ifdef CONFIG_INTEL_IOMMU
 	/* Disable ppgtt on SNB if VT-d is on. */
 	if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped) {
 		DRM_INFO("Disabling PPGTT because VT-d is on\n");
-		return false;
+		return 0;
 	}
 #endif
 
-	/* Full ppgtt disabled by default for now due to issues. */
-	if (full)
-		return HAS_PPGTT(dev) && (i915.enable_ppgtt == 2);
-	else
-		return HAS_ALIASING_PPGTT(dev);
+	return HAS_ALIASING_PPGTT(dev) ? 1 : 0;
 }
 
 #define GEN6_PPGTT_PD_ENTRIES 512
@@ -2031,6 +2041,14 @@ int i915_gem_gtt_init(struct drm_device *dev)
 		 gtt->base.total >> 20);
 	DRM_DEBUG_DRIVER("GMADR size = %ldM\n", gtt->mappable_end >> 20);
 	DRM_DEBUG_DRIVER("GTT stolen size = %zdM\n", gtt->stolen_size >> 20);
+	/*
+	 * i915.enable_ppgtt is read-only, so do an early pass to validate the
+	 * user's requested state against the hardware/driver capabilities.  We
+	 * do this now so that we can print out any log messages once rather
+	 * than every time we check intel_enable_ppgtt().
+	 */
+	i915.enable_ppgtt = sanitize_enable_ppgtt(dev, i915.enable_ppgtt);
+	DRM_DEBUG_DRIVER("ppgtt mode: %i\n", i915.enable_ppgtt);
 
 	return 0;
 }