usb: device: remove loopback function in favor of new device stack

This function is used for testing purposes only, there is no real use
for it in a user application. Remove in favor of implementation in new
device stack.
Also remove the part of the documentation that depends on loopback.
Documentation on how to implement your own USB device function using the
new USB device support will follow during the documentation rework.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>

Author: jfischer-no

doc/connectivity/usb/device/usb_device.rst

@@ -389,61 +389,6 @@ BOS descriptor and handled by the stack.
 
 See :zephyr:code-sample:`legacy-webusb` sample for reference.
 
-Implementing a non-standard USB class
-*************************************
-
-The configuration of USB device is done in the stack layer.
-
-The following structures and callbacks need to be defined:
-
-* Part of USB Descriptor table
-* USB Endpoint configuration table
-* USB Device configuration structure
-* Endpoint callbacks
-* Optionally class, vendor and custom handlers
-
-For example, for the USB loopback application:
-
-.. literalinclude:: ../../../../subsys/usb/device/class/loopback.c
-   :language: c
-   :start-after: usb.rst config structure start
-   :end-before: usb.rst config structure end
-   :linenos:
-
-Endpoint configuration:
-
-.. literalinclude:: ../../../../subsys/usb/device/class/loopback.c
-   :language: c
-   :start-after: usb.rst endpoint configuration start
-   :end-before: usb.rst endpoint configuration end
-   :linenos:
-
-USB Device configuration structure:
-
-.. literalinclude:: ../../../../subsys/usb/device/class/loopback.c
-   :language: c
-   :start-after: usb.rst device config data start
-   :end-before: usb.rst device config data end
-   :linenos:
-
-
-The vendor device requests are forwarded by the USB stack core driver to the
-class driver through the registered vendor handler.
-
-For the loopback class driver, :c:func:`loopback_vendor_handler` processes
-the vendor requests:
-
-.. literalinclude:: ../../../../subsys/usb/device/class/loopback.c
-   :language: c
-   :start-after: usb.rst vendor handler start
-   :end-before:  usb.rst vendor handler end
-   :linenos:
-
-The class driver waits for the :makevar:`USB_DC_CONFIGURED` device status code
-before transmitting any data.
-
-.. _testing_USB_native_sim:
-
 Interface number and endpoint address assignment
 ************************************************
 
@@ -508,6 +453,8 @@ prevent you from implementing a hardware-clone firmware. Instead, if possible,
 the host driver implementation should be fixed to use values from the interface
 and endpoint descriptor.
 
+.. _testing_USB_native_sim:
+
 Testing over USBIP in native_sim
 ********************************
 

subsys/usb/device/Kconfig

@@ -95,7 +95,6 @@ config USB_REQUEST_BUFFER_SIZE
 	range 8 65536
 	default 256 if USB_DEVICE_NETWORK_RNDIS
 	default 266 if (USB_DEVICE_BLUETOOTH && USB_DEVICE_BLUETOOTH_BIG_BUF)
-	default 1024 if USB_DEVICE_LOOPBACK
 	default 128
 
 config USB_MAX_ALT_SETTING

subsys/usb/device/class/CMakeLists.txt

@@ -3,7 +3,6 @@
 zephyr_sources_ifdef(CONFIG_USB_CDC_ACM cdc_acm.c)
 zephyr_sources_ifdef(CONFIG_USB_MASS_STORAGE msc.c)
 zephyr_sources_ifdef(CONFIG_USB_DEVICE_BLUETOOTH bluetooth.c)
-zephyr_sources_ifdef(CONFIG_USB_DEVICE_LOOPBACK loopback.c)
 
 add_subdirectory_ifdef(CONFIG_USB_DEVICE_AUDIO audio)
 add_subdirectory_ifdef(CONFIG_USB_DEVICE_NETWORK netusb)

subsys/usb/device/class/Kconfig

@@ -9,8 +9,6 @@ source "subsys/usb/device/class/Kconfig.msc"
 
 source "subsys/usb/device/class/Kconfig.bt"
 
-source "subsys/usb/device/class/Kconfig.test"
-
 source "subsys/usb/device/class/netusb/Kconfig"
 
 source "subsys/usb/device/class/hid/Kconfig"