drm/fourcc: Add drm_format_info_bpp() helper

Add a helper to retrieve the actual number of bits per pixel for a
plane, taking into account the number of characters and pixels per
block for tiled formats.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_fourcc.c

···
 EXPORT_SYMBOL(drm_format_info_block_height);
 
 /**
+ * drm_format_info_bpp - number of bits per pixel
+ * @info: pixel format info
+ * @plane: plane index
+ *
+ * Returns:
+ * The actual number of bits per pixel, depending on the plane index.
+ */
+unsigned int drm_format_info_bpp(const struct drm_format_info *info, int plane)
+{
+	if (!info || plane < 0 || plane >= info->num_planes)
+		return 0;
+
+	return info->char_per_block[plane] * 8 /
+	       (drm_format_info_block_width(info, plane) *
+		drm_format_info_block_height(info, plane));
+}
+EXPORT_SYMBOL(drm_format_info_bpp);
+
+/**
  * drm_format_info_min_pitch - computes the minimum required pitch in bytes
  * @info: pixel format info
  * @plane: plane index

include/drm/drm_fourcc.h

···
 					 int plane);
 unsigned int drm_format_info_block_height(const struct drm_format_info *info,
 					  int plane);
+unsigned int drm_format_info_bpp(const struct drm_format_info *info, int plane);
 uint64_t drm_format_info_min_pitch(const struct drm_format_info *info,
 				   int plane, unsigned int buffer_width);