[ftdi] Add function to detach ftdi_sio driver

This function was written with the help of claude code.

Signed-off-by: Douglas Reis <doreis@lowrisc.org>

Author: engdoreis

lib/ftdi/kernel_driver.cc

@@ -0,0 +1,61 @@
+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "kernel_driver.hh"
+
+#include <libudev.h>
+#include <libusb-1.0/libusb.h>
+
+#include <iostream>
+
+namespace ftdi {
+
+enum { kFtdiVid = 0x0403 };
+
+// Use libusb to temporarily detach ftdi_sio from every interface of
+// every FTDI USB device.  The kernel driver is re-attached automatically when
+// the D2XX / libft4222 handle is closed.
+void detach_ftdi_kernel_drivers(uint16_t pid) {
+  libusb_context* ctx = nullptr;
+  if (libusb_init(&ctx) != LIBUSB_SUCCESS) {
+    std::cerr << "libusb_init failed\n";
+    return;
+  }
+
+  libusb_device** devs = nullptr;
+  ssize_t cnt          = libusb_get_device_list(ctx, &devs);
+  if (cnt < 0) {
+    libusb_exit(ctx);
+    return;
+  }
+
+  for (ssize_t i = 0; i < cnt; i++) {
+    libusb_device_descriptor desc{};
+    if (libusb_get_device_descriptor(devs[i], &desc) != LIBUSB_SUCCESS) continue;
+    if (desc.idVendor != kFtdiVid || desc.idProduct != pid) continue;
+
+    libusb_device_handle* handle = nullptr;
+    if (libusb_open(devs[i], &handle) != LIBUSB_SUCCESS) continue;
+
+    libusb_config_descriptor* config = nullptr;
+    if (libusb_get_active_config_descriptor(devs[i], &config) == LIBUSB_SUCCESS) {
+      for (uint8_t j = 0; j < config->bNumInterfaces; j++) {
+        if (libusb_kernel_driver_active(handle, j) != 1) continue;
+        int ret = libusb_detach_kernel_driver(handle, j);
+        if (ret != LIBUSB_SUCCESS) {
+          std::cerr << "Failed to detach kernel driver on interface " << (int)j << ": "
+                    << libusb_error_name(ret) << "\n";
+        }
+      }
+      libusb_free_config_descriptor(config);
+    }
+
+    libusb_close(handle);
+  }
+
+  libusb_free_device_list(devs, 1);
+  libusb_exit(ctx);
+}
+
+}  // namespace ftdi

lib/ftdi/kernel_driver.hh

@@ -0,0 +1,19 @@
+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include <cstdint>
+#include <format>
+#include <string>
+#include <vector>
+
+namespace ftdi {
+
+// Option A: Detach ftdi_sio (or any kernel driver) from all FTDI USB interfaces
+// using libusb. This allows the D2XX library to claim the device afterwards.
+// Requires write access to the USB device files — install 99-ftditool.rules.
+void detach_ftdi_kernel_drivers(uint16_t pid);
+
+}  // namespace ftdi