drm/i915: set up PIPECONF explicitly for i9xx/vlv platforms

Same reasons as for the previous patch, just no bug report about
anything going wrong yet: We only support exactly the mode we program,
so don't leave any stale BIOS state behind.

Again this will be fun to properly track for fastboot.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -4736,7 +4736,7 @@ static void i9xx_set_pipeconf(struct intel_crtc *intel_crtc)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	uint32_t pipeconf;
 
-	pipeconf = I915_READ(PIPECONF(intel_crtc->pipe));
+	pipeconf = 0;
 
 	if (intel_crtc->pipe == 0 && INTEL_INFO(dev)->gen < 4) {
 		/* Enable pixel doubling when the dot clock is > 90% of the (display)
@@ -4748,15 +4748,10 @@ static void i9xx_set_pipeconf(struct intel_crtc *intel_crtc)
 		if (intel_crtc->config.requested_mode.clock >
 		    dev_priv->display.get_display_clock_speed(dev) * 9 / 10)
 			pipeconf |= PIPECONF_DOUBLE_WIDE;
-		else
-			pipeconf &= ~PIPECONF_DOUBLE_WIDE;
 	}
 
 	/* only g4x and later have fancy bpc/dither controls */
 	if (IS_G4X(dev) || IS_VALLEYVIEW(dev)) {
-		pipeconf &= ~(PIPECONF_BPC_MASK |
-			      PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_MASK);
-
 		/* Bspec claims that we can't use dithering for 30bpp pipes. */
 		if (intel_crtc->config.dither && intel_crtc->config.pipe_bpp != 30)
 			pipeconf |= PIPECONF_DITHER_EN |
@@ -4784,23 +4779,17 @@ static void i9xx_set_pipeconf(struct intel_crtc *intel_crtc)
 			pipeconf |= PIPECONF_CXSR_DOWNCLOCK;
 		} else {
 			DRM_DEBUG_KMS("disabling CxSR downclocking\n");
-			pipeconf &= ~PIPECONF_CXSR_DOWNCLOCK;
 		}
 	}
 
-	pipeconf &= ~PIPECONF_INTERLACE_MASK;
 	if (!IS_GEN2(dev) &&
 	    intel_crtc->config.adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE)
 		pipeconf |= PIPECONF_INTERLACE_W_FIELD_INDICATION;
 	else
 		pipeconf |= PIPECONF_PROGRESSIVE;
 
-	if (IS_VALLEYVIEW(dev)) {
-		if (intel_crtc->config.limited_color_range)
-			pipeconf |= PIPECONF_COLOR_RANGE_SELECT;
-		else
-			pipeconf &= ~PIPECONF_COLOR_RANGE_SELECT;
-	}
+	if (IS_VALLEYVIEW(dev) && intel_crtc->config.limited_color_range)
+		pipeconf |= PIPECONF_COLOR_RANGE_SELECT;
 
 	I915_WRITE(PIPECONF(intel_crtc->pipe), pipeconf);
 	POSTING_READ(PIPECONF(intel_crtc->pipe));