drm/i915: fix to setup display reference clock control on Ironlake

For new stepping of PCH, the display reference clock
is fully under driver's control. This one trys to setup
all needed reference clock for different outputs. Older
stepping of PCH chipset should be ignoring this.

This fixes output failure issue on newer PCH which requires
driver to take control of reference clock enabling.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -2158,11 +2158,11 @@
 #define  DREF_CPU_SOURCE_OUTPUT_MASK		(3<<13)
 #define  DREF_SSC_SOURCE_DISABLE                (0<<11)
 #define  DREF_SSC_SOURCE_ENABLE                 (2<<11)
-#define  DREF_SSC_SOURCE_MASK			(2<<11)
+#define  DREF_SSC_SOURCE_MASK			(3<<11)
 #define  DREF_NONSPREAD_SOURCE_DISABLE          (0<<9)
 #define  DREF_NONSPREAD_CK505_ENABLE		(1<<9)
 #define  DREF_NONSPREAD_SOURCE_ENABLE           (2<<9)
-#define  DREF_NONSPREAD_SOURCE_MASK		(2<<9)
+#define  DREF_NONSPREAD_SOURCE_MASK		(3<<9)
 #define  DREF_SUPERSPREAD_SOURCE_DISABLE        (0<<7)
 #define  DREF_SUPERSPREAD_SOURCE_ENABLE         (2<<7)
 #define  DREF_SSC4_DOWNSPREAD                   (0<<6)

drivers/gpu/drm/i915/intel_display.c

@@ -2814,6 +2814,46 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 				  link_bw, &m_n);
 	}
 
+	/* Ironlake: try to setup display ref clock before DPLL
+	 * enabling. This is only under driver's control after
+	 * PCH B stepping, previous chipset stepping should be
+	 * ignoring this setting.
+	 */
+	if (IS_IGDNG(dev)) {
+		temp = I915_READ(PCH_DREF_CONTROL);
+		/* Always enable nonspread source */
+		temp &= ~DREF_NONSPREAD_SOURCE_MASK;
+		temp |= DREF_NONSPREAD_SOURCE_ENABLE;
+		I915_WRITE(PCH_DREF_CONTROL, temp);
+		POSTING_READ(PCH_DREF_CONTROL);
+
+		temp &= ~DREF_SSC_SOURCE_MASK;
+		temp |= DREF_SSC_SOURCE_ENABLE;
+		I915_WRITE(PCH_DREF_CONTROL, temp);
+		POSTING_READ(PCH_DREF_CONTROL);
+
+		udelay(200);
+
+		if (is_edp) {
+			if (dev_priv->lvds_use_ssc) {
+				temp |= DREF_SSC1_ENABLE;
+				I915_WRITE(PCH_DREF_CONTROL, temp);
+				POSTING_READ(PCH_DREF_CONTROL);
+
+				udelay(200);
+
+				temp &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
+				temp |= DREF_CPU_SOURCE_OUTPUT_DOWNSPREAD;
+				I915_WRITE(PCH_DREF_CONTROL, temp);
+				POSTING_READ(PCH_DREF_CONTROL);
+			} else {
+				temp |= DREF_CPU_SOURCE_OUTPUT_NONSPREAD;
+				I915_WRITE(PCH_DREF_CONTROL, temp);
+				POSTING_READ(PCH_DREF_CONTROL);
+			}
+		}
+	}
+
 	if (IS_IGD(dev)) {
 		fp = (1 << clock.n) << 16 | clock.m1 << 8 | clock.m2;
 		if (has_reduced_clock)