* [PATCH v4l-utils 2/2] edid-decode: correct and complete AMD VSDB
2026-09-25 13:46 [PATCH 0/2] edid-decode: correct and complete AMD VSDB Julian Orth
2026-09-25 13:46 ` [PATCH v4l-utils 1/2] edid-decode: fix incorrect shift Julian Orth
@ 2026-09-25 13:46 ` Julian Orth
2026-09-28 8:24 ` [PATCH 0/2] " Hans Verkuil
2 siblings, 0 replies; 4+ messages in thread
From: Julian Orth @ 2026-09-25 13:46 UTC (permalink / raw)
To: linux-media, Julian Orth
This completes the work from 07632801b9d39d4fdb41a3346e74f88b16519fa2.
Sources:
- Reverse engineering of the AMD windows kernel driver.
- Patent US10706812B2 describes FreeSync 2 HDR and contains VSDB
examples.
- Various panel manufacturers have published or leaked data sheets that
contain annotated EDIDs. For example [1].
Changes:
- The bits in the flags bytes are now properly labeled and printed.
- Global backlight control is no longer advertised in version 3.
- x[12..=14] contain the maximum FSFT speed.
- x[4] is the MCCS VCP code.
- 3 of the flags from x[5] are no longer used in version 3.
- 1 of the flags from x[5] indicates SmartPower OLED support in version
3.
- x[5]&0x4 was previously labeled to indicate PQ support, but that was
incorrect and an artifact of how the windows driver converts these
bits.
- The meaning of PQ-Interim is now documented.
- x[5]&0x20 indicates HDR10 support in version 3.
- x[15] contains another DPCD offset that can be used by the source to
load information about the sink product and firmware checksum.
[1]: https://www.panelook.cn/upload/202601/NS160QDM-NZ1_Rev.P0_20241125_202601266620.pdf
Signed-off-by: Julian Orth <ju.orth@gmail.com>
---
utils/edid-decode/parse-cta-block.cpp | 291 ++++++++++++++++++----------------
1 file changed, 150 insertions(+), 141 deletions(-)
diff --git a/utils/edid-decode/parse-cta-block.cpp b/utils/edid-decode/parse-cta-block.cpp
index a52bc115..e083d968 100644
--- a/utils/edid-decode/parse-cta-block.cpp
+++ b/utils/edid-decode/parse-cta-block.cpp
@@ -1586,151 +1586,160 @@ static void cta_hf_sbtmdb(const unsigned char *x, unsigned length)
static void cta_amd(const unsigned char *x, unsigned length)
{
- // x[00] - major version
- // x[01] & 0x01 - unknown, set in almost all EDIDs
- // x[01] & 0x02 - set if x[05..=09] are valid
- // x[01] & 0x04 - global backlight control support
- // x[01] & 0x08 - local dimming support
- // x[01] & 0x10 - FreeSync Panel Replay/PSR switch support
- // x[01] & 0x20 - called the SPRS bit by AMD, related to Replay
- // x[01] & 0x40 - FreeSync Panel Replay support
- // x[01] & 0x80 - set if x[12..=14] are valid
- // x[02] - min refresh rate
- // x[03] - max refresh rate in versions < 3
- // x[04] - MCCS flags
- // -- start of version 2 fields
- // x[05] & 0x01 - unknown
- // x[05] & 0x02 - unknown
- // x[05] & 0x04 - PQ EOTF support
- // x[05] & 0x08 - unknown
- // x[05] & 0x10 - PQ-Interim EOTF support (unknown what that is but enumerated in ADL)
- // x[05] & 0x20 - unknown but see the calculation of supported_tf below
- // x[05] & 0xc0 - set to 1 if the display is Mini LED
- // set to 2 if the display is OLED
- // x[06] - max luminance
- // x[07] - min luminance
- // x[08] - if x[01] & 0x08 or display is OLED: max luminance without local dimming
- // else if x[01] & 0x04 : max luminance at min backlight
- // x[09] - if x[01] & 0x08 or display is OLED: min luminance without local dimming
- // else if x[01] & 0x04 : min luminance at min backlight
- // -- start of version 3 fields
- // x[10] - max refresh rate lower 8 bits in version >= 3
- // x[11] & 0x03 - max refresh rate upper 2 bits in version >= 3
- // x[11] & 0xfc - unused
- // -- end of version 3 mandatory fields, fields below will be parsed only if the VSDB
- // block is large enough
- // x[12] - unknown
- // x[13] - unknown
- // x[14] - unknown
- // x[15] & 0x80 - x[15] & 0x7f is valid
- // x[15] & 0x7f - unknown
- // x[16] & 0x80 - x[16] & 0x7f is valid
- // x[16] & 0x7f - DPCD (DisplayPort configuration data) register offset for
- // proprietary AMD settings
-
- if (length < 5) {
- printf(" Data block is truncated (length = %d)\n", length);
- return;
- }
-
- unsigned version = x[0];
+ // x[00] - major version
+ // x[01] & 0x01 - FreeSync support
+ // x[01] & 0x02 - FreeSync 2 HDR support, x[05..=09] are valid
+ // x[01] & 0x04 - In version 2: Global Backlight Control support
+ // In version 3: Reserved
+ // x[01] & 0x08 - Local Dimming Control support
+ // x[01] & 0x10 - In version 3: FreeSync Panel Replay/PSR switch support
+ // x[01] & 0x20 - In version 3: Dynamic Link Rate Control support
+ // x[01] & 0x40 - In version 3: FreeSync Panel Replay support
+ // x[01] & 0x80 - In version 3: FreeSync Fast Transport (FSFT) support, x[12..=14] are valid
+ // x[02] - min refresh rate
+ // x[03] - max refresh rate in versions < 3
+ // x[04] - MCCS VCP code
+ // -- start of version 2 fields
+ // x[05] & 0x01 - In version 2: sRGB EOTF support
+ // In version 3: Reserved
+ // x[05] & 0x02 - In version 2: BT.709 EOTF support
+ // In version 3: Reserved
+ // x[05] & 0x04 - Gamma 2.2 EOTF support
+ // x[05] & 0x08 - In version 2: Gamma 2.6 EOTF support
+ // In version 3: Reserved
+ // NOTE:
+ // The 4 EOTFs above use the native gamut and scale the input
+ // of the inverse EOTF such that output 0 maps to 0 luminance
+ // and output 1 maps to the max luminance.
+ // x[05] & 0x10 - In version 2:
+ // PQ-Interim EOTF support
+ // This uses the native gamut and an affine function is
+ // applied to the inverse EOTF output such that output 0 maps
+ // to the min luminance and output 1 maps to the max luminance.
+ // In version 3:
+ // SmartPower OLED support
+ // x[05] & 0x20 - In version 2: Reserved
+ // In version 3: HDR10 support
+ // x[05] & 0xc0 - In version 2: Reserved
+ // In version 3: set to 1 if the display is Mini LED
+ // set to 2 if the display is OLED
+ // value 3 is reserved
+ // x[06] - max luminance
+ // x[07] - min luminance
+ // x[08] - if x[01] & 0x08 or display is OLED: max luminance without local dimming
+ // else if x[01] & 0x04 : max luminance at min backlight
+ // x[09] - if x[01] & 0x08 or display is OLED: min luminance without local dimming
+ // else if x[01] & 0x04 : min luminance at min backlight
+ // -- start of version 3 fields
+ // x[10] - max refresh rate lower 8 bits in version >= 3
+ // x[11] & 0x03 - max refresh rate upper 2 bits in version >= 3
+ // x[11] & 0xfc - unused
+ // -- end of version 3 mandatory fields, fields below will be parsed only if the VSDB
+ // block is large enough
+ // x[12..=14] - FSFT maximum pixel clock in little-endian kHz.
+ // x[15] & 0x80 - x[15] & 0x7f is valid
+ // x[15] & 0x7f - DPCD (DisplayPort configuration data) register offset for
+ // additional display information. (Base = 0x403)
+ // x[16] & 0x80 - x[16] & 0x7f is valid
+ // x[16] & 0x7f - DPCD (DisplayPort configuration data) register offset for
+ // eDP display features handshake. (Base = 0x380)
+
+ if (length < 5) {
+ printf(" Data block is truncated (length = %d)\n", length);
+ return;
+ }
+
+ unsigned version = x[0];
printf(" Version: %u\n", version);
- printf(" Feature Caps: 0x%02x\n", x[1]);
- bool hdr_fields_valid = false;
- bool supports_local_dimming = false;
- bool has_global_backlight_control = false;
- if (version > 1) {
- hdr_fields_valid = x[1] & 0x02;
- has_global_backlight_control = x[1] & 0x04;
- supports_local_dimming = x[1] & 0x08;
- if (has_global_backlight_control)
- printf(" Global Backlight Control Supported\n");
- if (supports_local_dimming)
- printf(" Local Dimming Supported\n");
- if (version > 2) {
- // Obtained from:
- // https://github.com/torvalds/linux/commit/ec8e59cb4e0c1a52d5a541fff9dcec398b48f7b4
- if (x[1] & 0x40)
- printf(" FreeSync Panel Replay Supported\n");
- }
- }
-
- unsigned short max_refresh_rate;
- if (version > 2 && length > 0xb) {
- max_refresh_rate = (x[0xb] & 3) << 8 | x[0xa];
- } else {
- max_refresh_rate = x[3];
- }
+ printf(" Flags 1: 0x%02x\n", x[1]);
+ if (x[1] & 0x01)
+ printf(" FreeSync Supported\n");
+ if (x[1] & 0x02 && version > 1)
+ printf(" FreeSync 2 HDR Supported\n");
+ if (x[1] & 0x04 && version == 2)
+ printf(" Global Backlight Control Supported\n");
+ if (x[1] & 0x08 && version > 1)
+ printf(" Local Dimming Supported\n");
+ if (x[1] & 0x10 && version > 2)
+ printf(" Panel Replay/PSR Switch Supported\n");
+ if (x[1] & 0x20 && version > 2)
+ printf(" Dynamic Link Rate Control Supported\n");
+ if (x[1] & 0x40 && version > 2)
+ printf(" Panel Replay Supported\n");
+ if (x[1] & 0x80 && version > 2)
+ printf(" FreeSync Fast Transport Supported\n");
+
+ unsigned short max_refresh_rate;
+ if (version > 2 && length > 11) {
+ max_refresh_rate = (x[11] & 3) << 8 | x[10];
+ } else {
+ max_refresh_rate = x[3];
+ }
printf(" Minimum Refresh Rate: %u Hz\n", x[2]);
printf(" Maximum Refresh Rate: %u Hz\n", max_refresh_rate);
- // Freesync 1.x flags
- // One or more of the 0xe6 bits signal that the VESA MCCS
- // protocol is used to switch the Freesync range
- printf(" Flags 1.x: 0x%02x%s\n", x[4],
- (x[4] & 0xe6) ? " (MCCS)" : "");
-
- if (version < 2)
- return;
- if (length < 10) {
- printf(" Data block is truncated (length = %d)\n", length);
- return;
- }
-
- printf(" Flags 2.x: 0x%02x\n", x[5]);
-
- if (!hdr_fields_valid)
- return;
-
- const unsigned TF_PQ2084 = 0x0004;
- const unsigned TF_LINEAR_0_125 = 0x0020;
- const unsigned TF_GAMMA_22 = 0x0080;
-
- const unsigned CS_BT2020 = 0x0008;
-
- // the calculation of supported_tf is a bit weird because it doesn't correspond to
- // the description in the comment at the start of the function. but this is what ADL
- // (AMD Display Library) reports
- unsigned supported_tf = 0;
- unsigned supported_cs = 0;
- bool supports_hdr10 = x[5] & 0x34;
- if (supports_hdr10) {
- supported_tf |= TF_LINEAR_0_125 | TF_PQ2084;
- supported_cs |= CS_BT2020;
- }
- if (x[5] & 0x04)
- supported_tf |= TF_GAMMA_22;
-
- if (supported_tf & TF_PQ2084)
- printf(" ST 2084 (PQ) EOTF Supported\n");
- if (supported_tf & TF_LINEAR_0_125)
- printf(" Linear EOTF (Windows scRGB, 0.0 - 125.0) Supported\n");
- if (supported_tf & TF_GAMMA_22)
- printf(" Gamma 2.2 EOTF Supported\n");
-
- if (supported_cs & CS_BT2020)
- printf(" BT.2020 Gamut Supported\n");
-
- bool is_mini_led = x[5] >> 6 == 1;
- bool is_oled = x[5] >> 6 == 2;
- if (is_mini_led)
- printf(" Display is Mini LED\n");
- if (is_oled)
- printf(" Display is OLED\n");
-
- printf(" Maximum luminance: %u (%.3f cd/m^2)\n",
- x[6], 50.0 * pow(2, x[6] / 32.0));
- printf(" Minimum luminance: %u (%.3f cd/m^2)\n",
- x[7], (50.0 * pow(2, x[6] / 32.0)) * pow(x[7] / 255.0, 2) / 100.0);
- if (supports_local_dimming || is_oled || has_global_backlight_control) {
- const char *type = "minimum backlight";
- if (supports_local_dimming || is_oled)
- type = "without local dimming";
- printf(" Maximum luminance (%s): %u (%.3f cd/m^2)\n",
- type, x[8], 50.0 * pow(2, x[8] / 32.0));
- printf(" Minimum luminance (%s): %u (%.3f cd/m^2)\n",
- type, x[9], (50.0 * pow(2, x[8] / 32.0)) * pow(x[9] / 255.0, 2) / 100.0);
- }
+
+ if (x[4] != 0)
+ printf(" MCCS VCP Code: 0x%02x\n", x[4]);
+
+ if (version < 2)
+ return;
+ if (length < 10) {
+ printf(" Data block is truncated (length = %d)\n", length);
+ return;
+ }
+
+ printf(" Flags 5: 0x%02x\n", x[5]);
+ if (version >= 3) {
+ if (x[5] >> 6 == 1)
+ printf(" Display is Mini LED\n");
+ if (x[5] >> 6 == 2)
+ printf(" Display is OLED\n");
+ if (x[5] & 0x10)
+ printf(" SmartPower OLED Supported\n");
+ }
+ if (x[1] & 0x02) {
+ if (x[5] & 0x01 && version < 3)
+ printf(" sRGB EOTF Supported\n");
+ if (x[5] & 0x02 && version < 3)
+ printf(" BT.709 EOTF Supported\n");
+ if (x[5] & 0x04)
+ printf(" Gamma 2.2 EOTF Supported\n");
+ if (x[5] & 0x08 && version < 3)
+ printf(" Gamma 2.6 EOTF Supported\n");
+ if (x[5] & 0x10 && version < 3)
+ printf(" PQ-Interim EOTF Supported\n");
+ if (x[5] & 0x20 && version >= 3)
+ printf(" ST 2084 (PQ) EOTF Supported\n");
+
+ printf(" Maximum luminance: %u (%.3f cd/m^2)\n",
+ x[6], 50.0 * pow(2, x[6] / 32.0));
+ printf(" Minimum luminance: %u (%.3f cd/m^2)\n",
+ x[7], (50.0 * pow(2, x[6] / 32.0)) * pow(x[7] / 255.0, 2) / 100.0);
+ if (x[1] & 0x08 || (x[5] >> 6 == 2 && version > 2) || (x[1] & 0x04 && version == 2)) {
+ const char *type = "minimum backlight";
+ if (x[1] & 0x08 || (x[5] >> 6 == 2 && version > 2))
+ type = "without local dimming";
+ printf(" Maximum luminance (%s): %u (%.3f cd/m^2)\n",
+ type, x[8], 50.0 * pow(2, x[8] / 32.0));
+ printf(" Minimum luminance (%s): %u (%.3f cd/m^2)\n",
+ type, x[9], (50.0 * pow(2, x[8] / 32.0)) * pow(x[9] / 255.0, 2) / 100.0);
+ }
+ }
+
+ if (version < 3)
+ return;
+
+ if (length > 14 && x[1] & 0x80) {
+ unsigned khz = (unsigned)x[12] | ((unsigned)x[13] << 8) | ((unsigned)x[14] << 16);
+ printf(" FreeSync Fast Transport maximum pixel clock: %u kHz\n", khz);
+ }
+
+ if (length > 15 && x[15] & 0x80)
+ printf(" Additional Sink Information Address: 0x%x\n", 0x403 + (x[15] & 0x7f));
+
+ if (length > 16 && x[16] & 0x80)
+ printf(" eDP Display Features Handshake Address: 0x%x\n", 0x380 + (x[16] & 0x7f));
}
static std::string display_use_case(unsigned char x)
--
2.55.0
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