From 30c850db3f5f8c78c0c95a28ee9c5aa8788fbcd8 Mon Sep 17 00:00:00 2001
From: Comma Device <device@comma.ai>
Date: Sun, 18 Oct 2026 14:07:40 +0800
Subject: [PATCH] fix: release chestnut USB handle while modeld loads

---
 openpilot/system/hardware/chestnut/monitoring.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/openpilot/system/hardware/chestnut/monitoring.py b/openpilot/system/hardware/chestnut/monitoring.py
index 3a8b21f61..dae2b99ba 100644
--- a/openpilot/system/hardware/chestnut/monitoring.py
+++ b/openpilot/system/hardware/chestnut/monitoring.py
@@ -5,6 +5,7 @@ import usb1
 import openpilot.cereal.messaging as messaging
 from openpilot.cereal.services import SERVICE_LIST
 from openpilot.common.hardware.usb import CHESTNUT_USB_PRODUCT, get_usb_state, is_chestnut_usb_id
+from openpilot.common.params import Params
 
 
 def read_chestnut_state(handle, gpu_state=None):
@@ -26,11 +27,18 @@ def read_chestnut_state(handle, gpu_state=None):
 def chestnut_state_thread(end_event):
   pm = messaging.PubMaster(['chestnutState'])
   sm = messaging.SubMaster(['chestnutGpuState'])
+  params = Params()
   with usb1.USBContext() as context:
     handle = None
     try:
       while not end_event.is_set():
-        if handle is None:
+        # modeld owns the chestnut USB interface while loading/running the big model.
+        # Do not hold a second libusb handle: libusb_set_configuration returns EBUSY.
+        modeld_owns_usb = params.get_bool("ChestnutLoading") or params.get_bool("ChestnutActive")
+        if handle is not None and modeld_owns_usb:
+          handle.close()
+          handle = None
+        if handle is None and not modeld_owns_usb:
           devices = [d for d in get_usb_state() if is_chestnut_usb_id(d['vendorId'], d['productId']) and
                      d['product'] == CHESTNUT_USB_PRODUCT]
           if len(devices) == 1: