[PATCH v3 1/4] drm/edid: Parse AMD VSDB for FreeSync refresh range

[Alex Huang <Alex.Huang2@amd.com>]

Commit 118362a96286 ("drm/edid: Parse AMD Vendor-Specific Data Block")
added parsing of the AMD VSDB, but only for version 3 and only for the
replay/panel-type/luminance fields. Monitors that only advertise
FreeSync through a v1 or v2 AMD VSDB therefore get no variable refresh
rate range from the common EDID parser.

Restructure drm_parse_amd_vsdb() and implement parsing for the FreeSync
refresh range fields provided in the AMD VSDB. Additionally, version > 3
will be parsed as if they were version 3 (with a warning of this
occurring) as future versions will likely be backwards compatible.

Signed-off-by: Alex Huang <Alex.Huang2@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
 drivers/gpu/drm/drm_edid.c  | 147 +++++++++++++++++++++++++++++-------
 include/drm/drm_connector.h |  22 +++++-
 2 files changed, 139 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index df3c25bac761..a12b5e6905fb 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -101,20 +101,42 @@ enum drm_edid_internal_quirk {
 #define MICROSOFT_IEEE_OUI	0xca125c
 #define AMD_IEEE_OUI        0x00001A
 
+#define AMD_VSDB_V1_PAYLOAD_LEN 8
+#define AMD_VSDB_V2_PAYLOAD_LEN 13
 #define AMD_VSDB_V3_PAYLOAD_MIN_LEN 15
-#define AMD_VSDB_V3_PAYLOAD_MAX_LEN 20
+#define AMD_VSDB_V3_PAYLOAD_MAX_LEN 21
 
-struct amd_vsdb_v3_payload {
+#define AMD_VSDB_V3_MAX_VFREQ_EXT2_LEN 21
+
+struct amd_vsdb_common_payload {
 	u8 oui[3];
 	u8 version;
+} __packed;
+
+struct amd_vsdb_v1_payload {
+	struct amd_vsdb_common_payload common;
 	u8 feature_caps;
-	u8 rsvd0[3];
+	u8 min_vfreq;
+	u8 max_vfreq;
+	u8 freesync_vcp_code;
+} __packed;
+
+struct amd_vsdb_v2_payload {
+	struct amd_vsdb_v1_payload v1;
 	u8 cs_eotf_support;
 	u8 lum1_max;
 	u8 lum1_min;
 	u8 lum2_max;
 	u8 lum2_min;
-	u8 rsvd1[2];
+} __packed;
+
+struct amd_vsdb_v3_payload {
+	struct amd_vsdb_v2_payload v2;
+	u8 max_vfreq_ext_low;
+	/*
+	 * byte 14: bits 0-1 extend MSB of max refresh rate
+	 */
+	u8 max_vfreq_ext_high;
 	/*
 	 * Bytes beyond AMD_VSDB_V3_PAYLOAD_MIN_LEN are optional; a
 	 * monitor may provide a payload as short as 15 bytes.  Always
@@ -123,6 +145,12 @@ struct amd_vsdb_v3_payload {
 	u8 extra[AMD_VSDB_V3_PAYLOAD_MAX_LEN - AMD_VSDB_V3_PAYLOAD_MIN_LEN];
 } __packed;
 
+static const u8 amd_vsdb_min_len[] = {
+	[1] = AMD_VSDB_V1_PAYLOAD_LEN,
+	[2] = AMD_VSDB_V2_PAYLOAD_LEN,
+	[3] = AMD_VSDB_V3_PAYLOAD_MIN_LEN,
+};
+
 struct detailed_mode_closure {
 	struct drm_connector *connector;
 	const struct drm_edid *drm_edid;
@@ -5231,7 +5259,7 @@ static bool cea_db_is_microsoft_vsdb(const struct cea_db *db)
 static bool cea_db_is_amd_vsdb(const struct cea_db *db)
 {
 	return cea_db_is_vendor(db, AMD_IEEE_OUI) &&
-		cea_db_payload_len(db) >= AMD_VSDB_V3_PAYLOAD_MIN_LEN &&
+		cea_db_payload_len(db) >= AMD_VSDB_V1_PAYLOAD_LEN &&
 		cea_db_payload_len(db) <= AMD_VSDB_V3_PAYLOAD_MAX_LEN;
 }
 
@@ -6431,43 +6459,104 @@ static void drm_parse_microsoft_vsdb(struct drm_connector *connector,
 		    connector->base.id, connector->name, version, db[5]);
 }
 
+static void drm_parse_amd_vsdb_common(struct drm_display_info *info,
+				  const struct amd_vsdb_common_payload *data)
+{
+	info->amd_vsdb.version = data->version;
+}
+
+static void drm_parse_amd_vsdb_v1(struct drm_display_info *info,
+				  const struct amd_vsdb_v1_payload *data)
+{
+	info->amd_vsdb.freesync_supported = data->feature_caps & 0x1;
+	info->amd_vsdb.min_frame_rate = data->min_vfreq;
+	info->amd_vsdb.max_frame_rate = data->max_vfreq;
+	info->amd_vsdb.freesync_vcp_code = data->freesync_vcp_code;
+
+	drm_parse_amd_vsdb_common(info, &data->common);
+}
+
+static void drm_parse_amd_vsdb_v2(struct drm_display_info *info,
+				  const struct amd_vsdb_v2_payload *data)
+{
+	info->amd_vsdb.luminance_range1.max_luminance = data->lum1_max;
+	info->amd_vsdb.luminance_range1.min_luminance = data->lum1_min;
+	info->amd_vsdb.luminance_range2.max_luminance = data->lum2_max;
+	info->amd_vsdb.luminance_range2.min_luminance = data->lum2_min;
+
+	drm_parse_amd_vsdb_v1(info, &data->v1);
+}
+
+static void drm_parse_amd_vsdb_v3(struct drm_display_info *info,
+				  const struct amd_vsdb_v3_payload *data,
+				  int payload_len)
+{
+	u16 max_frame_rate;
+
+	info->amd_vsdb.replay_mode = data->v2.v1.feature_caps & 0x40;
+	info->amd_vsdb.panel_type = (data->v2.cs_eotf_support & 0xC0) >> 6;
+
+	drm_parse_amd_vsdb_v2(info, &data->v2);
+
+	/* vfreq is provided in a different set of fields for v3. */
+	max_frame_rate = data->max_vfreq_ext_low |
+			 (data->max_vfreq_ext_high & 0x3) << 8;
+
+	/*
+	 * The AMD VSDB v3 payload length is variable (15..21 bytes).
+	 * All fields through max_vfreq_ext_high (byte 14) are always
+	 * present, but data->extra[] (bytes 15+) may not be, so any access
+	 * to extra[] must be guarded with a runtime length check to
+	 * avoid out-of-bounds reads on shorter (but spec-valid) payloads.
+	 */
+	if (payload_len >= AMD_VSDB_V3_MAX_VFREQ_EXT2_LEN)
+		max_frame_rate |= (data->extra[5] & 0x3) << 10;
+
+	info->amd_vsdb.max_frame_rate = max_frame_rate;
+}
+
 static void drm_parse_amd_vsdb(struct drm_connector *connector,
 			       const struct cea_db *db)
 {
 	struct drm_display_info *info = &connector->display_info;
 	const u8 *data = cea_db_data(db);
-	const struct amd_vsdb_v3_payload *p;
+	int payload_len = cea_db_payload_len(db);
+	u8 version;
 
-	p = (const struct amd_vsdb_v3_payload *)data;
+	version = ((const struct amd_vsdb_common_payload *)data)->version;
 
-	if (p->version != 0x03) {
+	if (version < 1) {
 		drm_dbg_kms(connector->dev,
 			    "[CONNECTOR:%d:%s] Unsupported AMD VSDB version %u\n",
-			    connector->base.id, connector->name, p->version);
+			    connector->base.id, connector->name, version);
 		return;
 	}
 
-	info->amd_vsdb.version = p->version;
-	info->amd_vsdb.replay_mode = p->feature_caps & 0x40;
-	info->amd_vsdb.panel_type = (p->cs_eotf_support & 0xC0) >> 6;
-	info->amd_vsdb.luminance_range1.max_luminance = p->lum1_max;
-	info->amd_vsdb.luminance_range1.min_luminance = p->lum1_min;
-	info->amd_vsdb.luminance_range2.max_luminance = p->lum2_max;
-	info->amd_vsdb.luminance_range2.min_luminance = p->lum2_min;
+	if ((version <= 3 && payload_len < amd_vsdb_min_len[version]) ||
+		(version > 3 && payload_len < AMD_VSDB_V3_PAYLOAD_MIN_LEN)) {
+		drm_dbg_kms(connector->dev,
+			    "[CONNECTOR:%d:%s] AMD VSDB v%u payload too short (%d bytes)\n",
+			    connector->base.id, connector->name, version, payload_len);
+		return;
+	}
 
-	/*
-	 * The AMD VSDB v3 payload length is variable (15..20 bytes).
-	 * All fields through p->rsvd1 (byte 14) are always present,
-	 * but p->extra[] (bytes 15+) may not be.  Any future access to
-	 * extra[] must be guarded with a runtime length check to avoid
-	 * out-of-bounds reads on shorter (but spec-valid) payloads.
-	 * For example:
-	 *
-	 *   int len = cea_db_payload_len(db);
-	 *
-	 *   if (len > AMD_VSDB_V3_PAYLOAD_MIN_LEN)
-	 *       info->amd_vsdb.foo = p->extra[0];
-	 */
+	switch (version) {
+	default:
+		drm_dbg_kms(connector->dev,
+				"[CONNECTOR:%d:%s] AMD VSDB v%u is unsupported, VSDB will be parsed as v3.\n",
+				connector->base.id, connector->name, version);
+		fallthrough;
+	case 3:
+		drm_parse_amd_vsdb_v3(info, (const struct amd_vsdb_v3_payload *)data,
+				      payload_len);
+		break;
+	case 2:
+		drm_parse_amd_vsdb_v2(info, (const struct amd_vsdb_v2_payload *)data);
+		break;
+	case 1:
+		drm_parse_amd_vsdb_v1(info, (const struct amd_vsdb_v1_payload *)data);
+		break;
+	}
 }
 
 static void drm_parse_cea_ext(struct drm_connector *connector,
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 5f5ca023cd65..0914a2bd8ef1 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -697,7 +697,7 @@ enum drm_bus_flags {
  * struct drm_amd_vsdb_info - AMD-specific VSDB information
  *
  * This structure holds information parsed from the AMD Vendor-Specific Data
- * Block (VSDB) version 3.
+ * Block (VSDB) versions 1 to 3.
  */
 struct drm_amd_vsdb_info {
 	/**
@@ -705,6 +705,26 @@ struct drm_amd_vsdb_info {
 	 */
 	u8 version;
 
+	/**
+	 * @freesync_supported: FreeSync (variable refresh rate) supported by panel
+	 */
+	bool freesync_supported;
+
+	/**
+	 * @min_frame_rate: FreeSync minimum refresh rate in Hz
+	 */
+	u16 min_frame_rate;
+
+	/**
+	 * @max_frame_rate: FreeSync maximum refresh rate in Hz
+	 */
+	u16 max_frame_rate;
+
+	/**
+	 * @freesync_vcp_code: MCCS VCP code for FreeSync
+	 */
+	u8 freesync_vcp_code;
+
 	/**
 	 * @replay_mode: Panel Replay supported
 	 */
-- 
2.34.1