Test 1 - EDID Spoofing for Android 4K

edid-override.nix

@@ -0,0 +1,74 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.kioskEdid;
+
+  overrideModule = types.submodule {
+    options = {
+      connector = mkOption {
+        type = types.str;
+        example = "HDMI-A-1";
+        description = ''
+          DRM connector name to apply the EDID override to.
+          Check `ls /sys/class/drm/` on target hardware to confirm the
+          exact name (e.g. HDMI-A-1, HDMI-A-2).
+        '';
+      };
+
+      edidFile = mkOption {
+        type = types.path;
+        description = ''
+          Path to the binary EDID file to force for this connector.
+        '';
+      };
+
+      forceConnected = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Also force this connector to be treated as connected
+          (video=<connector>:e), in case the real link reports
+          disconnected/garbled state through a splitter or wireless kit.
+        '';
+      };
+    };
+  };
+in
+{
+  options.services.kioskEdid = {
+    enable = mkEnableOption "forcing custom EDIDs on one or more display connectors";
+
+    overrides = mkOption {
+      type = types.listOf overrideModule;
+      default = [ ];
+      description = ''
+        List of per-connector EDID overrides to apply. Each entry gets its
+        own firmware file and its own drm.edid_firmware kernel param.
+      '';
+      example = literalExpression ''
+        [
+          { connector = "HDMI-A-1"; edidFile = ./android-4k30-edid.bin; }
+          { connector = "HDMI-A-2"; edidFile = ./android-4k30-edid.bin; }
+        ]
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    hardware.firmware = map
+      (o: pkgs.runCommand "kiosk-edid-firmware-${o.connector}" { } ''
+        mkdir -p $out/lib/firmware/edid
+        cp ${o.edidFile} $out/lib/firmware/edid/${o.connector}.bin
+      '')
+      cfg.overrides;
+
+    boot.kernelParams = flatten (map
+      (o:
+        [ "drm.edid_firmware=${o.connector}:edid/${o.connector}.bin" ]
+        ++ optional o.forceConnected "video=${o.connector}:e"
+      )
+      cfg.overrides);
+  };
+}

flake.nix

@@ -216,7 +216,18 @@
           hostName = "radiantwavekiosk-android";
           diskModule = ./disk-config.nix;
           upgradeFlakeRef = "git+https://gitea.radiantwavetech.com/RadiantWaveTech/KioskConfig.git#radiantwavekiosk-android";
-          extraModules = [./rotated_display.nix];
+          extraModules = [
+            ./rotated_display.nix
+            ./edid-override.nix
+            { services.kioskEdid = {
+                enable = true;
+                overrides = [
+                  { connector = "HDMI-A-1"; edidFile = ./android-4k30-edid.bin; }
+                  { connector = "HDMI-A-2"; edidFile = ./android-4k30-edid.bin; }
+                ];
+              };
+            }
+          ];
         };
         radiantwavekiosk-android-dev = mkKioskSystem {
           system = "x86_64-linux";
@@ -224,7 +235,18 @@
           hostName = "radiantwavekiosk-android-dev";
           diskModule = ./disk-config.nix;
           upgradeFlakeRef = "git+https://gitea.radiantwavetech.com/RadiantWaveTech/KioskConfig.git?ref=dev#radiantwavekiosk-android-dev";
-          extraModules = [./rotated_display.nix];
+          extraModules = [
+            ./rotated_display.nix
+            ./edid-override.nix
+            { services.kioskEdid = {
+                enable = true;
+                overrides = [
+                  { connector = "HDMI-A-1"; edidFile = ./android-4k30-edid.bin; }
+                  { connector = "HDMI-A-2"; edidFile = ./android-4k30-edid.bin; }
+                ];
+              };
+            }
+          ];
         };
         # Raspberry Pi 5.
         radiantwavekiosk-rpi = mkRpiKioskSystem {

force_4k30_portrait_only.py

@@ -0,0 +1,128 @@
+#!/usr/bin/env python3
+"""
+Forces 2160x3840 portrait @ 30Hz as the ONLY Detailed Timing Descriptor
+(DTD slot 1 / preferred timing) and strips the Video Data Block from the
+CTA-861 extension so no other video mode is advertised in any way.
+
+Usage:
+  python3 force_4k30_portrait_only.py donor.bin fixed.bin
+"""
+
+import sys
+
+
+def build_dtd(pixel_clock_khz, h_active, h_blank, h_sync_offset, h_sync_width,
+              v_active, v_blank, v_sync_offset, v_sync_width,
+              h_size_mm=0, v_size_mm=0, h_border=0, v_border=0,
+              interlaced=False, hsync_pos=True, vsync_pos=True):
+    pc = round(pixel_clock_khz / 10)  # EDID stores pixel clock in 10kHz units
+    dtd = bytearray(18)
+    dtd[0] = pc & 0xFF
+    dtd[1] = (pc >> 8) & 0xFF
+
+    dtd[2] = h_active & 0xFF
+    dtd[3] = h_blank & 0xFF
+    dtd[4] = ((h_active >> 8) << 4) | (h_blank >> 8)
+
+    dtd[5] = v_active & 0xFF
+    dtd[6] = v_blank & 0xFF
+    dtd[7] = ((v_active >> 8) << 4) | (v_blank >> 8)
+
+    dtd[8] = h_sync_offset & 0xFF
+    dtd[9] = h_sync_width & 0xFF
+    dtd[10] = ((v_sync_offset & 0xF) << 4) | (v_sync_width & 0xF)
+    dtd[11] = (((h_sync_offset >> 8) & 0x3) << 6) | \
+              (((h_sync_width >> 8) & 0x3) << 4) | \
+              (((v_sync_offset >> 4) & 0x3) << 2) | \
+              ((v_sync_width >> 4) & 0x3)
+
+    dtd[12] = h_size_mm & 0xFF
+    dtd[13] = v_size_mm & 0xFF
+    dtd[14] = ((h_size_mm >> 8) << 4) | (v_size_mm >> 8)
+
+    dtd[15] = h_border
+    dtd[16] = v_border
+
+    flags = 0x18  # digital separate sync
+    if interlaced:
+        flags |= 0x80
+    if hsync_pos:
+        flags |= 0x02
+    if vsync_pos:
+        flags |= 0x04
+    dtd[17] = flags
+
+    return dtd
+
+
+TAG_VIDEO = 2
+
+
+def strip_video_data_block(ext):
+    """Remove all Video Data Blocks from a CTA-861 extension block."""
+    dtd_offset = ext[2]
+    pos = 4  # skip 4-byte CTA header
+    blocks = []
+    while pos < dtd_offset:
+        tag = (ext[pos] >> 5) & 0x07
+        length = ext[pos] & 0x1F
+        block_data = bytes(ext[pos + 1:pos + 1 + length])
+        blocks.append((tag, length, block_data))
+        pos += 1 + length
+
+    blocks = [(t, l, d) for t, l, d in blocks if t != TAG_VIDEO]
+
+    new_db = bytearray()
+    for tag, length, data in blocks:
+        new_db.append((tag << 5) | length)
+        new_db.extend(data)
+
+    new_ext = bytearray(128)
+    new_ext[0] = ext[0]  # CTA tag
+    new_ext[1] = ext[1]  # revision
+    new_ext[2] = 4 + len(new_db)  # new DTD offset
+    new_ext[3] = ext[3]  # flags (audio, YCbCr, etc.)
+    new_ext[4:4 + len(new_db)] = new_db
+
+    new_ext[0x7F] = 0
+    new_ext[0x7F] = (-sum(new_ext)) % 256
+    return new_ext
+
+
+if __name__ == "__main__":
+    infile, outfile = sys.argv[1], sys.argv[2]
+    data = bytearray(open(infile, "rb").read())
+
+    # --- 2160x3840 portrait @ 30Hz ---
+    # H blanking uses CVT-RB-style fixed values (front 48 / sync 32 / back 80)
+    # V blanking computed to satisfy CVT-RB min vertical blank time (~460us)
+    # Pixel clock ~= htotal * vtotal * refresh
+    dtd_4k30 = build_dtd(
+        pixel_clock_khz=271020,
+        h_active=2160, h_blank=160, h_sync_offset=48, h_sync_width=32,
+        v_active=3840, v_blank=54, v_sync_offset=3, v_sync_width=5,
+        h_size_mm=685, v_size_mm=1218,  # swapped panel physical size for portrait
+    )
+
+    # Slot 1 = bytes 54-71 (was 1920x1080@60, the preferred timing)
+    data[54:72] = dtd_4k30
+
+    # Slot 2 = bytes 72-89 (was 1280x720@60) - blank out to a dummy
+    # descriptor so no second timing is advertised at all.
+    # Dummy Descriptor format: 00 00 00 10 00, then 13 zero-padding bytes.
+    dummy = bytearray(18)
+    dummy[3] = 0x10  # tag byte for "Dummy Descriptor"
+    data[72:90] = dummy
+
+    # Unknown Display Descriptor slot and Product Name descriptor are
+    # left as-is.
+
+    # Recompute base block checksum (byte 127)
+    data[127] = (256 - sum(data[0:127]) % 256) % 256
+
+    # Strip Video Data Block from CTA-861 extension (bytes 128-255)
+    data[128:256] = strip_video_data_block(data[128:256])
+
+    open(outfile, "wb").write(data)
+    print(f"Wrote {outfile}")
+    print("Run `edid-decode` on the output to verify before flashing.")