[PATCH 1/4] drm/edid: Parse AMD VSDB for FreeSync refresh range
From: Alex Huang
Date: Tue Jul 21 2026 - 14:15:03 EST
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.
Signed-off-by: Alex Huang <Alex.Huang2@xxxxxxx>
---
drivers/gpu/drm/drm_edid.c | 134 ++++++++++++++++++++++++++++--------
include/drm/drm_connector.h | 22 +++++-
2 files changed, 126 insertions(+), 30 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index df3c25bac761..c9452066b9be 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -101,20 +101,58 @@ 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
+
+#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 {
+ u8 oui[3];
+ u8 version;
+ u8 feature_caps;
+ u8 min_vfreq;
+ u8 max_vfreq;
+ u8 freesync_vcp_code;
+} __packed;
+
+struct amd_vsdb_v2_payload {
+ u8 oui[3];
+ u8 version;
+ u8 feature_caps;
+ u8 min_vfreq;
+ u8 max_vfreq;
+ u8 freesync_vcp_code;
+ u8 cs_eotf_support;
+ u8 lum1_max;
+ u8 lum1_min;
+ u8 lum2_max;
+ u8 lum2_min;
+} __packed;
struct amd_vsdb_v3_payload {
u8 oui[3];
u8 version;
u8 feature_caps;
- u8 rsvd0[3];
+ u8 min_vfreq;
+ u8 max_vfreq;
+ u8 freesync_vcp_code;
u8 cs_eotf_support;
u8 lum1_max;
u8 lum1_min;
u8 lum2_max;
u8 lum2_min;
- u8 rsvd1[2];
+ 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
@@ -5231,7 +5269,7 @@ 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 +6469,81 @@ static void drm_parse_microsoft_vsdb(struct drm_connector *connector,
connector->base.id, connector->name, version, db[5]);
}
+static void drm_parse_amd_vsdb_v1(struct drm_display_info *info,
+ const u8 *data)
+{
+ const struct amd_vsdb_v1_payload *p =
+ (const struct amd_vsdb_v1_payload *)data;
+
+ info->amd_vsdb.freesync_supported = p->feature_caps & 0x1;
+ info->amd_vsdb.min_frame_rate = p->min_vfreq;
+ info->amd_vsdb.max_frame_rate = p->max_vfreq;
+ info->amd_vsdb.freesync_vcp_code = p->freesync_vcp_code;
+}
+
+static void drm_parse_amd_vsdb_v2(struct drm_display_info *info,
+ const u8 *data)
+{
+ const struct amd_vsdb_v2_payload *p =
+ (const struct amd_vsdb_v2_payload *)data;
+
+ 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;
+}
+
+static void drm_parse_amd_vsdb_v3(struct drm_display_info *info,
+ const u8 *data, int payload_len)
+{
+ const struct amd_vsdb_v3_payload *p =
+ (const struct amd_vsdb_v3_payload *)data;
+ u16 max_frame_rate;
+
+ info->amd_vsdb.replay_mode = p->feature_caps & 0x40;
+ info->amd_vsdb.panel_type = (p->cs_eotf_support & 0xC0) >> 6;
+
+ /* vfreq is provded in a different set of fields for v3. */
+ max_frame_rate = p->max_vfreq_ext_low |
+ (p->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 p->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 |= (p->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;
-
- p = (const struct amd_vsdb_v3_payload *)data;
+ const struct amd_vsdb_common_payload *common =
+ (const struct amd_vsdb_common_payload *)data;
- if (p->version != 0x03) {
+ if (common->version < 1 || common->version > 3) {
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, common->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;
+ info->amd_vsdb.version = common->version;
- /*
- * 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];
- */
+ drm_parse_amd_vsdb_v1(info, data);
+
+ if (common->version >= 2)
+ drm_parse_amd_vsdb_v2(info, data);
+
+ if (common->version >= 3)
+ drm_parse_amd_vsdb_v3(info, data, cea_db_payload_len(db));
}
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