[Intel-gfx] [PATCH 5/8] drm/i915: preserve SSC if previously set

[Jesse Barnes]

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.

Reported-by: Kristian Høgsberg <hoegsberg at gmail.com>
Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
---
 drivers/gpu/drm/i915/intel_display.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 479de3b..d450ab6 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5806,6 +5806,10 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
 	 */
 	val = I915_READ(PCH_DREF_CONTROL);
 
+	/* Preserve SSC if the BIOS set it */
+	if (val & DREF_SSC1_ENABLE)
+		i915.panel_use_ssc = 1;
+
 	/* As we must carefully and slowly disable/enable each source in turn,
 	 * compute the final state we want first and check if we need to
 	 * make any changes at all.
-- 
1.8.4.2