drm/i915: Give names to the CCK_DISPLAY_CLOCK_CONTROL bits

Avoid using magic values for CCK frequency bits. Also the mask we were
using for the requested frequency was one bit too short. Fix it up.

Note: This also fixes the #define for a mask (spotted by Jesse in his
review).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Add note about mask change.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -584,6 +584,11 @@ enum punit_power_well {
 #define  DSI_PLL_M1_DIV_SHIFT			0
 #define  DSI_PLL_M1_DIV_MASK			(0x1ff << 0)
 #define CCK_DISPLAY_CLOCK_CONTROL		0x6b
+#define  DISPLAY_TRUNK_FORCE_ON			(1 << 17)
+#define  DISPLAY_TRUNK_FORCE_OFF		(1 << 16)
+#define  DISPLAY_FREQUENCY_STATUS		(0x1f << 8)
+#define  DISPLAY_FREQUENCY_STATUS_SHIFT		8
+#define  DISPLAY_FREQUENCY_VALUES		(0x1f << 0)
 
 /**
  * DOC: DPIO

drivers/gpu/drm/i915/intel_display.c

@@ -4516,7 +4516,7 @@ static void valleyview_set_cdclk(struct drm_device *dev, int cdclk)
 		mutex_lock(&dev_priv->dpio_lock);
 		/* adjust cdclk divider */
 		val = vlv_cck_read(dev_priv, CCK_DISPLAY_CLOCK_CONTROL);
-		val &= ~0xf;
+		val &= ~DISPLAY_FREQUENCY_VALUES;
 		val |= divider;
 		vlv_cck_write(dev_priv, CCK_DISPLAY_CLOCK_CONTROL, val);
 		mutex_unlock(&dev_priv->dpio_lock);
@@ -4553,7 +4553,7 @@ int valleyview_cur_cdclk(struct drm_i915_private *dev_priv)
 	divider = vlv_cck_read(dev_priv, CCK_DISPLAY_CLOCK_CONTROL);
 	mutex_unlock(&dev_priv->dpio_lock);
 
-	divider &= 0xf;
+	divider &= DISPLAY_FREQUENCY_VALUES;
 
 	cur_cdclk = DIV_ROUND_CLOSEST(vco << 1, divider + 1);