[PATCH 4.9 115/116] drm/i915: skip the first 4k of stolen memory on everything >= gen8

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>

commit 6ba0566cf2afcdb17bff882e3a95cbbcb22c4a83 upstream.

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
Tested-by: Dominik Klementowski <dominik232@xxxxxxxxx>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
Acked-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/1481727338-9901-1-git-send-email-paulo.r.zanoni@xxxxxxxxx
(cherry picked from commit d43537610470d8829ebd17cd7842f47176e35ebd)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/i915_gem_stolen.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- 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
 		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);