drm/i915: skip the first 4k of stolen memory on everything >= gen8

BSpec got updated and this workaround is now listed as standard
required programming for all subsequent projects. This is confirmed to
fix Skylake screen flickering issues (probably caused by the fact that
we initialized a ring in the first page of stolen, but I didn't 100%
confirm this theory).

v2: this is the patch that fixes the screen flickering, document it.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94605
Cc: stable@vger.kernel.org
Tested-by: Dominik Klementowski <dominik232@gmail.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1481727338-9901-1-git-send-email-paulo.r.zanoni@intel.com
(cherry picked from commit d43537610470d8829ebd17cd7842f47176e35ebd)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index ebaa941c83afd7843a56287f2b857d8f8fd3a9fa..abc78bbfc1dcd0fbc6373222c3801929d1dfd2d4 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -55,10 +55,9 @@ int i915_gem_stolen_insert_node_in_range(struct drm_i915_private *dev_priv,
                return -ENODEV;
 
        /* See the comment at the drm_mm_init() call for more about this check.
-        * WaSkipStolenMemoryFirstPage:bdw,chv,kbl (incomplete)
+        * WaSkipStolenMemoryFirstPage:bdw+ (incomplete)
         */
-       if (start < 4096 && (IS_GEN8(dev_priv) ||
-                            IS_KBL_REVID(dev_priv, 0, KBL_REVID_A0)))
+       if (start < 4096 && INTEL_GEN(dev_priv) >= 8)
                start = 4096;
 
        mutex_lock(&dev_priv->mm.stolen_lock);