drm: Add mode_config .get_format_info() hook

Allow drivers to return a custom drm_format_info structure for special
fb layouts. We'll use this for the compression control surface in i915.

v2: Fix drm_get_format_info() kernel doc (Laurent)
    Don't pass 'dev' to the new hook (Laurent)
v3: s/compresssion/compression/ (Ben)

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170321181218.10042-4-ville.syrjala@linux.intel.com
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index ea169a90..579070f 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -34,6 +34,7 @@ struct drm_file;
 struct drm_device;
 struct drm_atomic_state;
 struct drm_mode_fb_cmd2;
+struct drm_format_info;
 
 /**
  * struct drm_mode_config_funcs - basic driver provided mode setting functions
@@ -70,6 +71,19 @@ struct drm_mode_config_funcs {
 					     const struct drm_mode_fb_cmd2 *mode_cmd);
 
 	/**
+	 * @get_format_info:
+	 *
+	 * Allows a driver to return custom format information for special
+	 * fb layouts (eg. ones with auxiliary compression control planes).
+	 *
+	 * RETURNS:
+	 *
+	 * The format information specific to the given fb metadata, or
+	 * NULL if none is found.
+	 */
+	const struct drm_format_info *(*get_format_info)(const struct drm_mode_fb_cmd2 *mode_cmd);
+
+	/**
 	 * @output_poll_changed:
 	 *
 	 * Callback used by helpers to inform the driver of output configuration