drm/i915: explicitly set up PIPECONF (and gamma table) on haswell

Again we don't really support different settings, so don't let the
BIOS sneak stuff through.

Since the motivation for this patch series is to ensure we have the
correct gamma table mode selected also add the required write to the
GAMMA_MODE register to select the 8bit legacy table.

And since I find lowercase letters in #defines offensive, also
bikeshed those.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
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

@@ -3672,9 +3672,9 @@
 #define _GAMMA_MODE_B		0x4ac80
 #define GAMMA_MODE(pipe) _PIPE(pipe, _GAMMA_MODE_A, _GAMMA_MODE_B)
 #define GAMMA_MODE_MODE_MASK	(3 << 0)
-#define GAMMA_MODE_MODE_8bit	(0 << 0)
-#define GAMMA_MODE_MODE_10bit	(1 << 0)
-#define GAMMA_MODE_MODE_12bit	(2 << 0)
+#define GAMMA_MODE_MODE_8BIT	(0 << 0)
+#define GAMMA_MODE_MODE_10BIT	(1 << 0)
+#define GAMMA_MODE_MODE_12BIT	(2 << 0)
 #define GAMMA_MODE_MODE_SPLIT	(3 << 0)
 
 /* interrupts */

drivers/gpu/drm/i915/intel_display.c

@@ -5437,13 +5437,11 @@ static void haswell_set_pipeconf(struct drm_crtc *crtc)
 	enum transcoder cpu_transcoder = intel_crtc->config.cpu_transcoder;
 	uint32_t val;
 
-	val = I915_READ(PIPECONF(cpu_transcoder));
+	val = 0;
 
-	val &= ~(PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_MASK);
 	if (intel_crtc->config.dither)
 		val |= (PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_SP);
 
-	val &= ~PIPECONF_INTERLACE_MASK_HSW;
 	if (intel_crtc->config.adjusted_mode.flags & DRM_MODE_FLAG_INTERLACE)
 		val |= PIPECONF_INTERLACED_ILK;
 	else
@@ -5451,6 +5449,9 @@ static void haswell_set_pipeconf(struct drm_crtc *crtc)
 
 	I915_WRITE(PIPECONF(cpu_transcoder), val);
 	POSTING_READ(PIPECONF(cpu_transcoder));
+
+	I915_WRITE(GAMMA_MODE(intel_crtc->pipe), GAMMA_MODE_MODE_8BIT);
+	POSTING_READ(GAMMA_MODE(intel_crtc->pipe));
 }
 
 static bool ironlake_compute_clocks(struct drm_crtc *crtc,