[PATCH v2 1/2] drm/edid: support Microsoft extension for HMDs and specialized monitors

[Philipp Zabel <philipp.zabel@gmail.com>]

Add minimal support for parsing VSDBs documented in Microsoft's "EDID
extension for head-mounted and specialized monitors" [1]. The version
field and the desktop usage flag can be used to set the non_desktop
connector property.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/display/specialized-monitors-edid-extension

Tested with HPN-36C1 and LEN-B800.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
---
Changes since v1 [2]:
 - Split out quirk removal into a separate patch.
 - Set non_desktop to true instead of 1.

[2] https://lore.kernel.org/all/20211213184706.5776-1-philipp.zabel@gmail.com/
---
 drivers/gpu/drm/drm_edid.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 12893e7be89b..271b5616cfaf 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -93,6 +93,8 @@ static int oui(u8 first, u8 second, u8 third)
 /* Non desktop display (i.e. HMD) */
 #define EDID_QUIRK_NON_DESKTOP			(1 << 12)
 
+#define MICROSOFT_IEEE_OUI	0xca125c
+
 struct detailed_mode_closure {
 	struct drm_connector *connector;
 	struct edid *edid;
@@ -4222,6 +4224,17 @@ static bool cea_db_is_hdmi_forum_vsdb(const u8 *db)
 	return oui(db[3], db[2], db[1]) == HDMI_FORUM_IEEE_OUI;
 }
 
+static bool cea_db_is_microsoft_vsdb(const u8 *db)
+{
+	if (cea_db_tag(db) != VENDOR_BLOCK)
+		return false;
+
+	if (cea_db_payload_len(db) != 21)
+		return false;
+
+	return oui(db[3], db[2], db[1]) == MICROSOFT_IEEE_OUI;
+}
+
 static bool cea_db_is_vcdb(const u8 *db)
 {
 	if (cea_db_tag(db) != USE_EXTENDED_TAG)
@@ -5149,6 +5162,25 @@ drm_parse_hdmi_vsdb_video(struct drm_connector *connector, const u8 *db)
 	drm_parse_hdmi_deep_color_info(connector, db);
 }
 
+/*
+ * See EDID extension for head-mounted and specialized monitors, specified at:
+ * https://docs.microsoft.com/en-us/windows-hardware/drivers/display/specialized-monitors-edid-extension
+ */
+static void drm_parse_microsoft_vsdb(struct drm_connector *connector,
+				     const u8 *db)
+{
+	struct drm_display_info *info = &connector->display_info;
+	u8 version = db[4];
+	bool desktop_usage = db[5] & BIT(6);
+
+	/* Version 1 and 2 for HMDs, version 3 flags desktop usage explicitly */
+	if (version == 1 || version == 2 || (version == 3 && !desktop_usage))
+		info->non_desktop = true;
+
+	drm_dbg_kms(connector->dev, "HMD or specialized display VSDB version %u: 0x%02x\n",
+		    version, db[5]);
+}
+
 static void drm_parse_cea_ext(struct drm_connector *connector,
 			      const struct edid *edid)
 {
@@ -5179,6 +5211,8 @@ static void drm_parse_cea_ext(struct drm_connector *connector,
 			drm_parse_hdmi_vsdb_video(connector, db);
 		if (cea_db_is_hdmi_forum_vsdb(db))
 			drm_parse_hdmi_forum_vsdb(connector, db);
+		if (cea_db_is_microsoft_vsdb(db))
+			drm_parse_microsoft_vsdb(connector, db);
 		if (cea_db_is_y420cmdb(db))
 			drm_parse_y420cmdb_bitmap(connector, db);
 		if (cea_db_is_vcdb(db))

base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
-- 
2.34.1