Once EDID is parsed, the monitor HDMI support information is cached in
drm_display_info.is_hdmi by drm_parse_hdmi_vsdb_video().

This driver calls drm_detect_hdmi_monitor() to receive the same
information and stores its own cached value in
vc4_hdmi_encoder.hdmi_monitor, which is less efficient.

Avoid calling drm_detect_hdmi_monitor() and use drm_display_info.is_hdmi
instead. This also allows to remove vc4_hdmi_encoder.hdmi_monitor.

drm_detect_hdmi_monitor() is called in vc4_hdmi_connector_detect() and
vc4_hdmi_connector_get_modes(). In both cases it is safe to rely on
drm_display_info.is_hdmi as shown by ftrace:

$ sudo trace-cmd record -p function_graph -l "vc4_hdmi_*" -l "drm_*"

vc4_hdmi_connector_detect:

    vc4_hdmi_connector_detect() {
      drm_get_edid() {
        drm_connector_update_edid_property() {
          drm_add_display_info() {
            drm_reset_display_info();
            drm_for_each_detailed_block.part.0();
            drm_parse_cea_ext() {
              drm_find_cea_extension();
              drm_parse_hdmi_vsdb_video();
              /* drm_display_info.is_hdmi is cached here */
            }
          }
        }
      }
      /* drm_display_info.is_hdmi is used here */
    }

vc4_hdmi_connector_get_modes:

    vc4_hdmi_connector_get_modes() {
      drm_get_edid() {
        drm_connector_update_edid_property() {
          drm_add_display_info() {
            drm_reset_display_info();
            drm_for_each_detailed_block.part.0();
            drm_parse_cea_ext() {
              drm_find_cea_extension();
              drm_parse_hdmi_vsdb_video();
              /* drm_display_info.is_hdmi is cached here */
            }
          }
        }
      }
      /* drm_display_info.is_hdmi is used here */
      drm_connector_update_edid_property();
    }
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420114500.187664-2-jose.exposito89@gmail.com