drm/i915/bdw: Broadwell has PIPEMISC

And it inherits some bits from the previous TRANS_CONF (aka PIPE_CONF
on previous gens).

v2: Rebase on to of the pipe config bpp handling rework.

v3: Rebased on top of the pipe_config->dither refactoring.

v4: Drop the read-modify-write cycle for PIPEMISC, similarly to how we
now also build up PIPECONF completely ourselves - keeping around
random stuff set by the BIOS just isn't a good idea. I've checked BDW
BSpec and we already set all relevant bits.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> (v1)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -3237,6 +3237,18 @@
 #define PIPEFRAMEPIXEL(pipe)  _PIPE(pipe, _PIPEAFRAMEPIXEL, _PIPEBFRAMEPIXEL)
 #define PIPESTAT(pipe) _PIPE(pipe, _PIPEASTAT, _PIPEBSTAT)
 
+#define _PIPE_MISC_A			0x70030
+#define _PIPE_MISC_B			0x71030
+#define   PIPEMISC_DITHER_BPC_MASK	(7<<5)
+#define   PIPEMISC_DITHER_8_BPC		(0<<5)
+#define   PIPEMISC_DITHER_10_BPC	(1<<5)
+#define   PIPEMISC_DITHER_6_BPC		(2<<5)
+#define   PIPEMISC_DITHER_12_BPC	(3<<5)
+#define   PIPEMISC_DITHER_ENABLE	(1<<4)
+#define   PIPEMISC_DITHER_TYPE_MASK	(3<<2)
+#define   PIPEMISC_DITHER_TYPE_SP	(0<<2)
+#define PIPEMISC(pipe) _PIPE(pipe, _PIPE_MISC_A, _PIPE_MISC_B)
+
 #define VLV_DPFLIPSTAT				(VLV_DISPLAY_BASE + 0x70028)
 #define   PIPEB_LINE_COMPARE_INT_EN		(1<<29)
 #define   PIPEB_HLINE_INT_EN			(1<<28)

drivers/gpu/drm/i915/intel_display.c

@@ -5818,14 +5818,16 @@ static void intel_set_pipe_csc(struct drm_crtc *crtc)
 
 static void haswell_set_pipeconf(struct drm_crtc *crtc)
 {
-	struct drm_i915_private *dev_priv = crtc->dev->dev_private;
+	struct drm_device *dev = crtc->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	enum pipe pipe = intel_crtc->pipe;
 	enum transcoder cpu_transcoder = intel_crtc->config.cpu_transcoder;
 	uint32_t val;
 
 	val = 0;
 
-	if (intel_crtc->config.dither)
+	if (IS_HASWELL(dev) && intel_crtc->config.dither)
 		val |= (PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_SP);
 
 	if (intel_crtc->config.adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE)
@@ -5838,6 +5840,33 @@ static void haswell_set_pipeconf(struct drm_crtc *crtc)
 
 	I915_WRITE(GAMMA_MODE(intel_crtc->pipe), GAMMA_MODE_MODE_8BIT);
 	POSTING_READ(GAMMA_MODE(intel_crtc->pipe));
+
+	if (IS_BROADWELL(dev)) {
+		val = 0;
+
+		switch (intel_crtc->config.pipe_bpp) {
+		case 18:
+			val |= PIPEMISC_DITHER_6_BPC;
+			break;
+		case 24:
+			val |= PIPEMISC_DITHER_8_BPC;
+			break;
+		case 30:
+			val |= PIPEMISC_DITHER_10_BPC;
+			break;
+		case 36:
+			val |= PIPEMISC_DITHER_12_BPC;
+			break;
+		default:
+			/* Case prevented by pipe_config_set_bpp. */
+			BUG();
+		}
+
+		if (intel_crtc->config.dither)
+			val |= PIPEMISC_DITHER_ENABLE | PIPEMISC_DITHER_TYPE_SP;
+
+		I915_WRITE(PIPEMISC(pipe), val);
+	}
 }
 
 static bool ironlake_compute_clocks(struct drm_crtc *crtc,