speedup chestnut probe (#38596)

use link-up in scons

openpilot/selfdrive/modeld/SConscript

@@ -1,7 +1,6 @@
 import glob
 import json
 import os
-import sys, subprocess
 import time
 from SCons.Script import Action, Value
 from openpilot.common.file_chunker import chunk_file, get_chunk_targets, get_existing_chunks
@@ -88,18 +87,13 @@ for usbgpu in [False, True] if USBGPU else [False]:
   onnx_sizes_sum = sum(os.path.getsize(f) for f in driving_onnx_deps)
   chunk_targets = get_chunk_targets(target_pkl_path, estimate_pickle_max_size(onnx_sizes_sum))
   def do_compile(target, source, env, command=cmd, pkl=target_pkl_path, chunks=chunk_targets):
+    from openpilot.system.hardware.chestnut.flash import link_up
     # chestnut can enumerate before its PCIe link is up due to varying 12V power behavior across cars
-    probe_cmd = [sys.executable, '-c', 'from openpilot.selfdrive.modeld.compile_modeld import Device; Device[Device.DEFAULT]']
-    probe_env = {**env['ENV'], 'DEV': 'USB+AMD'}
-    ready = False
-    for attempt in range(3):
-      if attempt: time.sleep(1)
-      try:
-        ready = subprocess.run(probe_cmd, env=probe_env, capture_output=True, timeout=10).returncode == 0
-      except subprocess.TimeoutExpired:
-        pass
-      if ready: break
-    if not ready:
+    for _ in range(10):
+      if link_up():
+        break
+      time.sleep(1)
+    else:
       print("Chestnut not ready, skipping big model build")
       return
     if ret := env.Execute(command):

openpilot/system/hardware/chestnut/flash.py

@@ -104,6 +104,26 @@ def open_device(path):
   return os.open(f"/dev/bus/usb/{bus:03d}/{dev:03d}", os.O_RDWR)
 
 
+def link_up() -> bool:
+  # asm enumerates on USB-C alone, gpu is only usable once pcie link is up
+  try:
+    path, _, _ = find_chestnut()
+    if path is None:
+      return False
+    fd = open_device(path)
+  except (OSError, RuntimeError):
+    return False
+  try:
+    fcntl.ioctl(fd, USBDEVFS_CONTROL, Ctrl(0x40, 0xF3, 1, 0, 0, 2000, None))
+    buf = (ctypes.c_ubyte * 1)()
+    fcntl.ioctl(fd, USBDEVFS_CONTROL, Ctrl(0xC0, 0xE4, 0xB450, 0, 1, 1000, ctypes.cast(buf, ctypes.c_void_p)))
+    return buf[0] == 0x78  # LTSSM L0
+  except OSError:
+    return False
+  finally:
+    os.close(fd)
+
+
 def claim_interface(path, setup=False):
   # unbind usb-storage, which binds to the ROM bootloader
   disable_runtime_pm(path)