From 92122789b2d699a1e82dca502940e0dd37bf6f3b Mon Sep 17 00:00:00 2001
From: Jesse Barnes <jbarnes@virtuousgeek.org>
Date: Thu, 9 Oct 2014 12:57:42 -0700
Subject: [PATCH] drm/i915: preserve SSC if previously set v3
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Some machines may have a broken VBT or no VBT at all, but we still want
to use SSC there. So check for it and keep it enabled if we see it
already on. Based on an earlier fix from Kristian.
v2: honor modparam if set too (Daniel)
read out at init time and store for panel_use_ssc() use (Jesse)
v3: trust BIOS configuration over VBT like we do for DP (Jani)
Reported-by: Kristian Høgsberg <hoegsberg@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/i915/intel_display.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e183a26cd738..eac54c6db11f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13331,6 +13331,7 @@ void intel_modeset_setup_hw_state(struct drm_device *dev,
void intel_modeset_gem_init(struct drm_device *dev)
{
+ struct drm_i915_private *dev_priv = dev->dev_private;
struct drm_crtc *c;
struct drm_i915_gem_object *obj;
@@ -13338,6 +13339,16 @@ void intel_modeset_gem_init(struct drm_device *dev)
intel_init_gt_powersave(dev);
mutex_unlock(&dev->struct_mutex);
+ /*
+ * There may be no VBT; and if the BIOS enabled SSC we can
+ * just keep using it to avoid unnecessary flicker. Whereas if the
+ * BIOS isn't using it, don't assume it will work even if the VBT
+ * indicates as much.
+ */
+ if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
+ dev_priv->vbt.lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
+ DREF_SSC1_ENABLE);
+
intel_modeset_init_hw(dev);
intel_setup_overlay(dev);
--
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