drm/edid: add helper for HDMI VSDB audio latency field length

Add a helper for skipping the HDMI VSDB audio latency fields.

There's a functional change for HDMI VSDB blocks that do not respect the
spec: "I_Latency_Fields_Present shall be zero if Latency_Fields_Present
is zero". We assume this to hold when skipping the latency fields, and
ignore non-zero I_Latency_Fields_Present if Latency_Fields_Present is
zero.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/da4293203ef2ddeb0bf66a2bfdbc129ab609c543.1672826282.git.jani.nikula@intel.com

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 847076b..93067b8 100644 (file)
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -4695,6 +4695,16 @@ static bool hdmi_vsdb_i_latency_present(const u8 *db)
        return hdmi_vsdb_latency_present(db) && db[8] & BIT(6);
 }
 
+static int hdmi_vsdb_latency_length(const u8 *db)
+{
+       if (hdmi_vsdb_i_latency_present(db))
+               return 4;
+       else if (hdmi_vsdb_latency_present(db))
+               return 2;
+       else
+               return 0;
+}
+
 /*
  * do_hdmi_vsdb_modes - Parse the HDMI Vendor Specific data block
  * @connector: connector corresponding to the HDMI sink
@@ -4720,13 +4730,7 @@ do_hdmi_vsdb_modes(struct drm_connector *connector, const u8 *db, u8 len)
        if (!(db[8] & (1 << 5)))
                goto out;
 
-       /* Latency_Fields_Present */
-       if (db[8] & (1 << 7))
-               offset += 2;
-
-       /* I_Latency_Fields_Present */
-       if (db[8] & (1 << 6))
-               offset += 2;
+       offset += hdmi_vsdb_latency_length(db);
 
        /* the declared length is not long enough for the 2 first bytes
         * of additional video format capabilities */