wip: Automatically detach ftdi_sio driver

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

Author: engdoreis

app/main.cc

@@ -21,8 +21,8 @@
 
 using Action = std::function<int()>;
 
-static std::vector<ftdi::DeviceInfo> scan() {
-  auto result = ftdi::Discovery::scan();
+static std::vector<ftdi::DeviceInfo> scan(uint16_t pid = 0x6010) {
+  auto result = ftdi::Discovery::scan(pid);
   if (!result) {
     std::cerr << "Error: Failed to communicate with FTDI driver." << std::endl;
     exit(0);

flake.nix

@@ -42,7 +42,7 @@
             ft4222
             libmpsse
           ];
-          buildInputs = [ft4222 libmpsse ftd2xx];
+          buildInputs = with pkgs; [ft4222 libmpsse ftd2xx libusb1 systemd];
           shellHook = ''
             # Setting LD_LIBRARY_PATH for libftd2xx
             export LD_LIBRARY_PATH="${ftd2xx}/lib:$LD_LIBRARY_PATH"

lib/ftdi/CMakeLists.txt

@@ -8,6 +8,7 @@ target_sources(ftdipp
     PRIVATE
         spi_host.cc
         gpio.cc
+        kernel_driver.cc
     PUBLIC
         FILE_SET HEADERS
         BASE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}
@@ -16,6 +17,7 @@ target_sources(ftdipp
             spi_host.hh
             gpio.hh
             log.hh
+            kernel_driver.hh
 )
 
 target_include_directories(ftdipp
@@ -25,7 +27,8 @@ target_include_directories(ftdipp
 )
 
 target_link_libraries(ftdipp
-    PUBLIC magic_enum::magic_enum embeddedpp mpsse ft4222 
+    PUBLIC magic_enum::magic_enum embeddedpp mpsse ft4222
+    PRIVATE usb-1.0 udev
 )
 target_compile_options(ftdipp PRIVATE "-fno-exceptions")
 

lib/ftdi/ftdi.hh

@@ -5,11 +5,11 @@
 #pragma once
 
 #include "ftd2xx.h"
-#include <cstdint>
 #include <optional>
 #include <vector>
 #include <iostream>
 #include "device_info.hh"
+#include "kernel_driver.hh"
 
 namespace ftdi {
 
@@ -19,7 +19,11 @@ class Discovery {
    * @brief Scans for all connected FTDI devices.
    * @return A vector of devices if successful, or std::nullopt if the driver call failed.
    */
-  static std::optional<std::vector<DeviceInfo>> scan() {
+
+  static std::optional<std::vector<DeviceInfo>> scan(uint16_t pid) {
+    // Detach ftdi_sio (if present) so D2XX can enumerate the device.
+    detach_ftdi_kernel_drivers(pid);
+
     DWORD num_devs = 0;
 
     // 1. Get the number of devices

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

nix/ftditool.nix

@@ -12,6 +12,8 @@
   argparse,
   magic-enum,
   picosha2,
+  libusb1,
+  systemd,
   makeWrapper,
 }:
 stdenv.mkDerivation {
@@ -33,6 +35,8 @@ stdenv.mkDerivation {
     magic-enum
     picosha2
     ftd2xx
+    libusb1
+    systemd
   ];
 
   cmakeFlags = [