From e36445fa5feb4db65586186ec823a225339b8885 Mon Sep 17 00:00:00 2001
From: Keith Burzinski <kbx81x@gmail.com>
Date: Sat, 5 Sep 2026 06:00:25 -0500
Subject: [PATCH] [usb_uart] Keep the comm interface number valid when its
 claim fails (#18968)

---
 esphome/components/usb_uart/usb_uart.cpp | 12 +++++++-----
 esphome/components/usb_uart/usb_uart.h   |  3 +++
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/esphome/components/usb_uart/usb_uart.cpp b/esphome/components/usb_uart/usb_uart.cpp
index cf66e4c369..60b7fe4e9c 100644
--- a/esphome/components/usb_uart/usb_uart.cpp
+++ b/esphome/components/usb_uart/usb_uart.cpp
@@ -434,11 +434,12 @@ void USBUartTypeCdcAcm::on_connected() {
       auto err_comm = usb_host_interface_claim(this->handle_, this->device_handle_,
                                                channel->cdc_dev_.interrupt_interface_number, 0);
       if (err_comm != ESP_OK) {
+        // Continue anyway: the interface number stays valid for CDC request addressing
         ESP_LOGW(TAG, "Could not claim comm interface %d: %s", channel->cdc_dev_.interrupt_interface_number,
                  esp_err_to_name(err_comm));
-        channel->cdc_dev_.interrupt_interface_number = 0xFF;  // Mark as unavailable, but continue anyway
       } else {
         ESP_LOGD(TAG, "Claimed comm interface %d", channel->cdc_dev_.interrupt_interface_number);
+        channel->cdc_dev_.interrupt_interface_claimed = true;
       }
     }
     auto err =
@@ -465,14 +466,15 @@ void USBUartTypeCdcAcm::on_disconnected() {
       usb_host_endpoint_halt(this->device_handle_, channel->cdc_dev_.out_ep->bEndpointAddress);
       usb_host_endpoint_flush(this->device_handle_, channel->cdc_dev_.out_ep->bEndpointAddress);
     }
-    if (channel->cdc_dev_.notify_ep != nullptr) {
+    // Only tear down the notify pipe when we claimed its interface ourselves;
+    // no transfer is ever submitted on it, so there is nothing else to cancel.
+    if (channel->cdc_dev_.notify_ep != nullptr && channel->cdc_dev_.interrupt_interface_claimed) {
       usb_host_endpoint_halt(this->device_handle_, channel->cdc_dev_.notify_ep->bEndpointAddress);
       usb_host_endpoint_flush(this->device_handle_, channel->cdc_dev_.notify_ep->bEndpointAddress);
     }
-    if (channel->cdc_dev_.interrupt_interface_number != 0xFF &&
-        channel->cdc_dev_.interrupt_interface_number != channel->cdc_dev_.bulk_interface_number) {
+    if (channel->cdc_dev_.interrupt_interface_claimed) {
       usb_host_interface_release(this->handle_, this->device_handle_, channel->cdc_dev_.interrupt_interface_number);
-      channel->cdc_dev_.interrupt_interface_number = 0xFF;
+      channel->cdc_dev_.interrupt_interface_claimed = false;
     }
     usb_host_interface_release(this->handle_, this->device_handle_, channel->cdc_dev_.bulk_interface_number);
     // Reset the input and output started flags to their initial state to avoid the possibility of spurious restarts
diff --git a/esphome/components/usb_uart/usb_uart.h b/esphome/components/usb_uart/usb_uart.h
index 00b34fb942..9d87bf964c 100644
--- a/esphome/components/usb_uart/usb_uart.h
+++ b/esphome/components/usb_uart/usb_uart.h
@@ -34,7 +34,10 @@ struct CdcEps {
   const usb_ep_desc_t *in_ep;
   const usb_ep_desc_t *out_ep;
   uint8_t bulk_interface_number;
+  // Also the wIndex target for CDC class requests (SET_LINE_CODING etc.), so it
+  // must remain valid even when the interface itself is not claimed.
   uint8_t interrupt_interface_number;
+  bool interrupt_interface_claimed{false};
 };
 
 enum CH34xChipType : uint8_t {