drm/i915/tv: Deobfuscate preferred mode selection

Rewrite the preferred mode selection to just check
whether the TV modes is HD or SD. For SD TV modes we
favor 480 line modes, for 720p we prefer 720 line modes,
and for 1080i/p we prefer 1080 line modes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181112170000.27531-10-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/intel_tv.c

@@ -859,6 +859,14 @@ intel_tv_mode_valid(struct drm_connector *connector,
 	return MODE_CLOCK_RANGE;
 }
 
+static int
+intel_tv_mode_vdisplay(const struct tv_mode *tv_mode)
+{
+	if (tv_mode->progressive)
+		return tv_mode->nbr_end + 1;
+	else
+		return 2 * (tv_mode->nbr_end + 1);
+}
 
 static void
 intel_tv_get_config(struct intel_encoder *encoder,
@@ -1097,10 +1105,7 @@ static void intel_tv_pre_enable(struct intel_encoder *encoder,
 	/* Filter ctl must be set before TV_WIN_SIZE */
 	I915_WRITE(TV_FILTER_CTL_1, TV_AUTO_SCALE);
 	xsize = tv_mode->hblank_start - tv_mode->hblank_end;
-	if (tv_mode->progressive)
-		ysize = tv_mode->nbr_end + 1;
-	else
-		ysize = 2 * (tv_mode->nbr_end + 1);
+	ysize = intel_tv_mode_vdisplay(tv_mode);
 
 	xpos = conn_state->tv.margins.left;
 	ypos = conn_state->tv.margins.top;
@@ -1319,22 +1324,28 @@ static const struct input_res {
 	{"1920x1080", 1920, 1080},
 };
 
-/*
- * Chose preferred mode  according to line number of TV format
- */
-static void
-intel_tv_choose_preferred_modes(const struct tv_mode *tv_mode,
-			       struct drm_display_mode *mode_ptr)
+/* Choose preferred mode according to line number of TV format */
+static bool
+intel_tv_is_preferred_mode(const struct drm_display_mode *mode,
+			   const struct tv_mode *tv_mode)
 {
-	if (tv_mode->nbr_end < 480 && mode_ptr->vdisplay == 480)
-		mode_ptr->type |= DRM_MODE_TYPE_PREFERRED;
-	else if (tv_mode->nbr_end > 480) {
-		if (tv_mode->progressive == true && tv_mode->nbr_end < 720) {
-			if (mode_ptr->vdisplay == 720)
-				mode_ptr->type |= DRM_MODE_TYPE_PREFERRED;
-		} else if (mode_ptr->vdisplay == 1080)
-				mode_ptr->type |= DRM_MODE_TYPE_PREFERRED;
-	}
+	int vdisplay = intel_tv_mode_vdisplay(tv_mode);
+
+	/* prefer 480 line modes for all SD TV modes */
+	if (vdisplay <= 576)
+		vdisplay = 480;
+
+	return vdisplay == mode->vdisplay;
+}
+
+static void
+intel_tv_set_mode_type(struct drm_display_mode *mode,
+		       const struct tv_mode *tv_mode)
+{
+	mode->type = DRM_MODE_TYPE_DRIVER;
+
+	if (intel_tv_is_preferred_mode(mode, tv_mode))
+		mode->type |= DRM_MODE_TYPE_PREFERRED;
 }
 
 static int
@@ -1382,8 +1393,7 @@ intel_tv_get_modes(struct drm_connector *connector)
 		tmp = div_u64(tmp, 1000000);
 		mode_ptr->clock = (int) tmp;
 
-		mode_ptr->type = DRM_MODE_TYPE_DRIVER;
-		intel_tv_choose_preferred_modes(tv_mode, mode_ptr);
+		intel_tv_set_mode_type(mode_ptr, tv_mode);
 		drm_mode_probed_add(connector, mode_ptr);
 		count++;
 	}