diff --git a/drivers/gpu/drm/asahi/m3/m3_soc.rs b/drivers/gpu/drm/asahi/m3/m3_soc.rs
index 4b81475612b6fa..7500822c4124c5 100644
--- a/drivers/gpu/drm/asahi/m3/m3_soc.rs
+++ b/drivers/gpu/drm/asahi/m3/m3_soc.rs
@@ -291,6 +291,7 @@ pub(crate) static T8122: Soc = Soc {
     cores_per_cluster: 10,
     mailbox_compatibles: &[
         b"apple,t8122-agx-asc-mailbox\0",
+        b"apple,t8122-agx-asc-mailbox\0apple,asc-mailbox-v4\0",
         b"apple,t8122-asc-mailbox\0apple,asc-mailbox-v4\0",
     ],
     mailbox_interrupts: &[0, 723, 4, 0, 724, 4, 0, 725, 4, 0, 726, 4],
diff --git a/tools/asahi/test-m3-mailbox.py b/tools/asahi/test-m3-mailbox.py
new file mode 100644
index 00000000000000..2320d17f10f6f4
--- /dev/null
+++ b/tools/asahi/test-m3-mailbox.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-only OR MIT
+"""Exercise the production T8122 mailbox predicate with captured DTB properties.
+
+Usage: python3 tools/asahi/test-m3-mailbox.py [runtime.dtb daily.dtb]
+Requires dtc's fdtget. No target access or MMIO.
+"""
+import hashlib
+import os
+from pathlib import Path
+import re
+import subprocess
+import sys
+import tempfile
+
+ROOT = Path(__file__).resolve().parents[2]
+board = (ROOT / 'drivers/gpu/drm/asahi/m3/m3_board.rs').read_text()
+soc = (ROOT / 'drivers/gpu/drm/asahi/m3/m3_soc.rs').read_text()
+t8122 = soc[soc.index('pub(crate) static T8122:'):]
+compatibles = re.search(r'mailbox_compatibles: &(\[.*?\]),', t8122, re.S)[1]
+irqs = re.search(r'mailbox_interrupts: &(\[.*?\]),', t8122, re.S)[1]
+base = re.search(r'mailbox: (0x[0-9a-fA-F_]+),', t8122)[1]
+regfn = re.search(r'fn expected_mailbox_reg\(.*?\n}', board, re.S)[0]
+predicate = board[board.index('    if !soc.mailbox_compatibles'):]
+predicate = predicate[:predicate.index('\n    {')].strip()[3:]
+
+
+def prop(dtb, node, name, kind):
+    result = subprocess.check_output(['fdtget', '-t', kind, str(dtb), node, name], text=True)
+    return [int(v, 16) for v in result.split()]
+
+
+def vec(values):
+    return 'vec![' + ','.join(map(str, values)) + ']'
+
+
+fixtures = []
+for argument in sys.argv[1:]:
+    dtb = Path(argument)
+    gpu = '/soc/gpu@292400000'
+    # Both retained captures use this mailbox path; verify the phandle link,
+    # not its capture-specific numeric value.
+    mbox = '/soc/mbox@292408000'
+    if prop(dtb, gpu, 'mboxes', 'x') != prop(dtb, mbox, 'phandle', 'x'):
+        raise RuntimeError('GPU mailbox phandle mismatch')
+    values = [prop(dtb, mbox, name, kind) for name, kind in
+              [('compatible', 'bx'), ('reg', 'x'), ('interrupt-names', 'bx'),
+               ('interrupts', 'x'), ('#mbox-cells', 'x')]]
+    if len(values[4]) != 1:
+        raise RuntimeError('bad #mbox-cells length')
+    fixtures.append('check(' + ','.join(vec(v) for v in values[:4]) + ',' + str(values[4][0]) + ');')
+    print(dtb.name, hashlib.sha256(dtb.read_bytes()).hexdigest())
+if not sys.argv[1:]:
+    # Public t8122-j613-dcp-25g83.dtsi and t8122-gpu.dtsi resource contract.
+    names = list(b'send-empty\0send-not-empty\0recv-empty\0recv-not-empty\0')
+    for compat in (b'apple,t8122-agx-asc-mailbox\0apple,asc-mailbox-v4\0',
+                   b'apple,t8122-asc-mailbox\0apple,asc-mailbox-v4\0'):
+        values = [list(compat), [2, 0x92408000, 0, 0x4000], names,
+                  [0,723,4,0,724,4,0,725,4,0,726,4]]
+        fixtures.append('check(' + ','.join(vec(v) for v in values) + ',0);')
+if len(fixtures) != 2:
+    raise SystemExit('supply runtime.dtb and daily.dtb')
+
+source = '''
+struct Windows { mailbox: u64 }
+struct Soc { mailbox_compatibles: &'static [&'static [u8]], mailbox_interrupts: &'static [u32], windows: Windows }
+''' + regfn + '''
+fn accepts(soc: &Soc, compat: &Vec<u8>, mbox_reg: &Vec<u32>, irq_names: &Vec<u8>, irqs: &Vec<u32>, cells: u32) -> bool {
+    !(''' + predicate + ''')
+}
+fn check(compat: Vec<u8>, reg: Vec<u32>, names: Vec<u8>, irqs: Vec<u32>, cells: u32) {
+    let soc = Soc { mailbox_compatibles: &''' + compatibles + ''', mailbox_interrupts: &''' + irqs + ''', windows: Windows { mailbox: ''' + base + ''' } };
+    let ok = |c: &Vec<u8>, r: &Vec<u32>, n: &Vec<u8>, i: &Vec<u32>, x| accepts(&soc,c,r,n,i,x);
+    assert!(ok(&compat,&reg,&names,&irqs,cells));
+    for i in 0..reg.len() { let mut v=reg.clone(); v[i]^=1; assert!(!ok(&compat,&v,&names,&irqs,cells)); }
+    for i in 0..irqs.len() { let mut v=irqs.clone(); v[i]^=1; assert!(!ok(&compat,&reg,&names,&v,cells)); }
+    assert!(!ok(&compat,&reg,&names,&irqs,1));
+    let mut v=names.clone(); v[0]^=1; assert!(!ok(&compat,&reg,&v,&irqs,cells));
+    for v in [b"apple,asc-mailbox-v4\\0".to_vec(), b"apple,t8122-agx-asc-mailbox\\0unknown\\0".to_vec(), b"apple,t6031-agx-asc-mailbox\\0".to_vec()] { assert!(!ok(&v,&reg,&names,&irqs,cells)); }
+    for v in soc.mailbox_compatibles { assert!(ok(&v.to_vec(),&reg,&names,&irqs,cells)); }
+}
+fn main() {
+''' + '\n'.join(fixtures) + '\nprintln!("mailbox: both captures, all exact supported lists and resource/identity mutation controls PASS");\n}\n'
+with tempfile.TemporaryDirectory() as tmp:
+    path = Path(tmp)
+    (path / 'test.rs').write_text(source)
+    subprocess.run([os.environ.get('RUSTC', 'rustc'), '--edition=2021', str(path / 'test.rs'), '-o', str(path / 'test')], check=True)
+    subprocess.run([str(path / 'test')], check=True)
+print('m3_board.rs', hashlib.sha256(board.encode()).hexdigest())
+print('m3_soc.rs', hashlib.sha256(soc.encode()).hexdigest())
diff --git a/tools/aurora-ci/host-tests.json b/tools/aurora-ci/host-tests.json
index a1b93d695dfd6e..017828e7865d44 100644
--- a/tools/aurora-ci/host-tests.json
+++ b/tools/aurora-ci/host-tests.json
@@ -2282,6 +2282,14 @@
     "{output}"
    ],
    "note": "Build only the host Kconfig tool in an isolated output directory; check all built-in/module dependency combinations."
+  },
+  {
+   "name": "tools/asahi/test-m3-mailbox.py",
+   "group": "tools",
+   "argv": [
+    "python3",
+    "tools/asahi/test-m3-mailbox.py"
+   ]
   }
  ],
  "helpers": {