usb: device_next: Document if callbacks are mandatory

Adds additional documentation to the callbacks of uac2_ops
to describe if/when they are mandatory to register.

Additionally add asserts before calling them to help debugging
if the user did not register the required ones.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>

include/zephyr/usb/class/usbd_uac2.h

@@ -47,6 +47,7 @@ struct uac2_ops {
 	 * @brief Start of Frame callback
 	 *
 	 * Notifies application about SOF event on the bus.
+	 * This callback is mandatory to register.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param user_data Opaque user data pointer
@@ -56,6 +57,7 @@ struct uac2_ops {
 	 * @brief Terminal update callback
 	 *
 	 * Notifies application that host has enabled or disabled a terminal.
+	 * This callback is mandatory to register.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param terminal Terminal ID linked to AudioStreaming interface
@@ -73,6 +75,7 @@ struct uac2_ops {
 	 * AudioStreaming interface. The buffer is owned by USB stack until
 	 * @ref data_recv_cb callback is called. The buffer must be sufficiently
 	 * aligned and otherwise suitable for use by UDC driver.
+	 * This callback is mandatory to register for devices receiving USB audio from the USB host.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param terminal Input Terminal ID linked to AudioStreaming interface
@@ -86,6 +89,7 @@ struct uac2_ops {
 	 *
 	 * This function releases buffer obtained in @ref get_recv_buf after USB
 	 * has written data to the buffer and/or no longer needs it.
+	 * This callback is mandatory to register for devices receiving USB audio from the USB host.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param terminal Input Terminal ID linked to AudioStreaming interface
@@ -100,6 +104,7 @@ struct uac2_ops {
 	 *
 	 * This function releases buffer provided in @ref usbd_uac2_send when
 	 * the class no longer needs it.
+	 * This callback is mandatory to register if calling @ref usbd_uac2_send.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param terminal Output Terminal ID linked to AudioStreaming interface
@@ -118,6 +123,9 @@ struct uac2_ops {
 	 * capable device is operating at Full-Speed (microframes was false),
 	 * the format is Q10.14 stored on 24 least significant bits (i.e. 8 most
 	 * significant bits are ignored).
+	 * This callback is mandatory to register if there is USB Audio Streaming interface linked
+	 * to Input Terminal clocked from asynchronous clock (i.e. clock source without
+	 * sof-synchronized;) and there is no implicit-feedback; on the interface.
 	 *
 	 * @param dev USB Audio 2 device
 	 * @param terminal Input Terminal ID whose feedback should be returned

subsys/usb/device_next/class/usbd_uac2.c

@@ -4,7 +4,11 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <stddef.h>
+#include <stdint.h>
+
 #include <zephyr/kernel.h>
+#include <zephyr/sys/__assert.h>
 #include <zephyr/sys/atomic.h>
 #include <zephyr/sys/byteorder.h>
 
@@ -209,9 +213,49 @@ static int terminal_to_as_interface(const struct device *dev, uint8_t terminal)
 void usbd_uac2_set_ops(const struct device *dev,
 		       const struct uac2_ops *ops, void *user_data)
 {
+	const struct uac2_cfg *cfg = dev->config;
 	struct uac2_ctx *ctx = dev->data;
 
 	__ASSERT(ops->sof_cb, "SOF callback is mandatory");
+	__ASSERT(ops->terminal_update_cb, "terminal_update_cb is mandatory");
+
+	for (uint8_t i = 0U; i < cfg->num_ifaces; i++) {
+		const uint16_t ep_idx = cfg->ep_indexes[i];
+
+		if (cfg->fb_indexes[i] != 0U) {
+			__ASSERT(ops->feedback_cb, "feedback_cb is mandatory");
+		}
+
+		if (ep_idx) {
+			const struct usb_ep_descriptor *desc = NULL;
+
+			if (cfg->fs_descriptors != NULL) {
+				/* If fs_descriptors is non-NULL and ep_idx is non-zero then
+				 * cfg->fs_descriptors[ep_idx] is non-NULL
+				 */
+				desc = (const struct usb_ep_descriptor *)
+					       cfg->fs_descriptors[ep_idx];
+			} else if (cfg->hs_descriptors != NULL) {
+				/* If hs_descriptors is non-NULL and ep_idx is non-zero then
+				 * cfg->hs_descriptors[ep_idx] is non-NULL
+				 */
+				desc = (const struct usb_ep_descriptor *)
+					       cfg->hs_descriptors[ep_idx];
+			}
+
+			if (desc != NULL) {
+				if (USB_EP_DIR_IS_OUT(desc->bEndpointAddress)) {
+					__ASSERT(ops->get_recv_buf, "get_recv_buf is mandatory");
+					__ASSERT(ops->data_recv_cb, "data_recv_cb is mandatory");
+				}
+
+				if (USB_EP_DIR_IS_IN(desc->bEndpointAddress)) {
+					__ASSERT(ops->buf_release_cb,
+						 "buf_release_cb is mandatory");
+				}
+			}
+		}
+	}
 
 	ctx->ops = ops;
 	ctx->user_data = user_data;