Re: [PATCH 1/1] drm/vc4: hdmi: Replace drm_detect_hdmi_monitor() with is_hdmi

Hi Jose,

On Wed, Apr 06, 2022 at 06:55:14PM +0200, José Expósito wrote:

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, which is less efficient.

Avoid calling drm_detect_hdmi_monitor() and use drm_display_info.is_hdmi instead.

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:

How do you use ftrace to generate that?

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();
          cea_db_offsets.part.0();
          cea_db_is_hdmi_vsdb.part.0();
          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();
          cea_db_offsets.part.0();
          cea_db_is_hdmi_vsdb.part.0();
          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

I think what you're hinting at in the cover letter would be best though: we should just remove that caching entirely and use is_hdmi everywhere

Maxime