drm: add helper functions for YCBCR420 handling

This patch adds helper functions for YCBCR 420 handling.
These functions do:
- check if a given video mode is YCBCR 420 only mode.
- check if a given video mode is YCBCR 420 also mode.

V2: Added YCBCR functions as helpers in DRM layer, instead of
keeping it in I915 layer.
V3: Added handling for YCBCR-420 only modes too.
V4: EXPORT_SYMBOL(drm_find_hdmi_output_type)
V5: Addressed review comments from Danvet:
- %s/drm_find_hdmi_output_type/drm_display_info_hdmi_output_type
- %s/drm_can_support_ycbcr_output/drm_display_supports_ycbcr_output
- %s/drm_can_support_this_ycbcr_output/
drm_display_supports_this_ycbcr_output
- pass drm_display_info instead of drm_connector for consistency
- For drm_get_highest_quality_ycbcr_supported doc, move the variable
description above, and then the function description.
V6: Add only YCBCR420 helpers (Ville)
V7: Addressed review comments from Ville
- Remove cea_vic_valid() check.
- Fix indentation.
- Make input parameters to helpers, const.

Cc: Ville Syrjala <[e-mail]>
Cc: Jose Abreu <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Signed-off-by: Shashank Sharma <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]
[vsyrjala: Fix sparse indentation warn]
Signed-off-by: Ville Syrjälä <[e-mail]>

drivers/gpu/drm/drm_modes.c

···
 out:
 	return ret;
 }
+
+/**
+ * drm_mode_is_420_only - if a given videomode can be only supported in YCBCR420
+ * output format
+ *
+ * @connector: drm connector under action.
+ * @mode: video mode to be tested.
+ *
+ * Returns:
+ * true if the mode can be supported in YCBCR420 format
+ * false if not.
+ */
+bool drm_mode_is_420_only(const struct drm_display_info *display,
+			  const struct drm_display_mode *mode)
+{
+	u8 vic = drm_match_cea_mode(mode);
+
+	return test_bit(vic, display->hdmi.y420_vdb_modes);
+}
+EXPORT_SYMBOL(drm_mode_is_420_only);
+
+/**
+ * drm_mode_is_420_also - if a given videomode can be supported in YCBCR420
+ * output format also (along with RGB/YCBCR444/422)
+ *
+ * @display: display under action.
+ * @mode: video mode to be tested.
+ *
+ * Returns:
+ * true if the mode can be support YCBCR420 format
+ * false if not.
+ */
+bool drm_mode_is_420_also(const struct drm_display_info *display,
+			  const struct drm_display_mode *mode)
+{
+	u8 vic = drm_match_cea_mode(mode);
+
+	return test_bit(vic, display->hdmi.y420_cmdb_modes);
+}
+EXPORT_SYMBOL(drm_mode_is_420_also);
+/**
+ * drm_mode_is_420 - if a given videomode can be supported in YCBCR420
+ * output format
+ *
+ * @display: display under action.
+ * @mode: video mode to be tested.
+ *
+ * Returns:
+ * true if the mode can be supported in YCBCR420 format
+ * false if not.
+ */
+bool drm_mode_is_420(const struct drm_display_info *display,
+		     const struct drm_display_mode *mode)
+{
+	return drm_mode_is_420_only(display, mode) ||
+		drm_mode_is_420_also(display, mode);
+}
+EXPORT_SYMBOL(drm_mode_is_420);

include/drm/drm_modes.h

···
 			   const struct drm_mode_modeinfo *in);
 void drm_mode_probed_add(struct drm_connector *connector, struct drm_display_mode *mode);
 void drm_mode_debug_printmodeline(const struct drm_display_mode *mode);
+bool drm_mode_is_420_only(const struct drm_display_info *display,
+			  const struct drm_display_mode *mode);
+bool drm_mode_is_420_also(const struct drm_display_info *display,
+			  const struct drm_display_mode *mode);
+bool drm_mode_is_420(const struct drm_display_info *display,
+		     const struct drm_display_mode *mode);
 
 struct drm_display_mode *drm_cvt_mode(struct drm_device *dev,
 				      int hdisplay, int vdisplay, int vrefresh,