From: Gary Wang <gary.c.wang@intel.com>
Date: Fri, 28 Aug 2015 16:40:34 +0800
Subject: drm/i915: set CDCLK if DPLL0 enabled during resuming from S3
Git-commit: 39d9b85a4d4fa1642663ca0d208b5c246a3d6f50
Patch-mainline: 4.3-rc1
References: boo#960021

Since BIOS RC 1.4 it would enable CDCLK PLL during BIOS S3 resume, then
driver needs to set CDCLK to avoid display corruption if DPLL0 enabled.

References: https://bugs.freedesktop.org/show_bug.cgi?id=91697
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Cooper Chiou <cooper.chiou@intel.com>
Reviewed-by: Wei Shun Chang <wei.shun.chang@intel.com>
Tested-by: Gary Wang <gary.c.wang@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gavin Hindman <gavin.hindman@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Xiong Y Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Gary Wang <gary.c.wang@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/intel_display.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5723,16 +5723,13 @@ void skl_init_cdclk(struct drm_i915_priv
 	/* enable PG1 and Misc I/O */
 	intel_display_power_get(dev_priv, POWER_DOMAIN_PLLS);
 
-	/* DPLL0 already enabed !? */
-	if (I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE) {
-		DRM_DEBUG_DRIVER("DPLL0 already running\n");
-		return;
+	/* DPLL0 not enabled (happens on early BIOS versions) */
+	if (!(I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE)) {
+		/* enable DPLL0 */
+		required_vco = skl_cdclk_get_vco(dev_priv->skl_boot_cdclk);
+		skl_dpll0_enable(dev_priv, required_vco);
 	}
 
-	/* enable DPLL0 */
-	required_vco = skl_cdclk_get_vco(dev_priv->skl_boot_cdclk);
-	skl_dpll0_enable(dev_priv, required_vco);
-
 	/* set CDCLK to the frequency the BIOS chose */
 	skl_set_cdclk(dev_priv, dev_priv->skl_boot_cdclk);
 
