usb: device_next: uac2: Double buffering on feedback endpoint

Enable double buffering on isochronous feedback endpoint to avoid
sending ZLP instead of feedback information.

Signed-off-by: Tomasz Moń <[email protected]>

Author: tmon-nordic

subsys/usb/device_next/class/usbd_uac2.c

@@ -29,7 +29,7 @@ LOG_MODULE_REGISTER(usbd_uac2, CONFIG_USBD_UAC2_LOG_LEVEL);
 		+ AS_HAS_ISOCHRONOUS_DATA_ENDPOINT(node) +			\
 		+ AS_IS_USB_ISO_IN(node) /* ISO IN double buffering */ +	\
 		+ AS_IS_USB_ISO_OUT(node) /* ISO OUT double buffering */ +	\
-		AS_HAS_EXPLICIT_FEEDBACK_ENDPOINT(node)))
+		2 * AS_HAS_EXPLICIT_FEEDBACK_ENDPOINT(node)))
 #define COUNT_UAC2_EP_BUFFERS(i)						\
 	+ DT_PROP(DT_DRV_INST(i), interrupt_endpoint)				\
 	DT_INST_FOREACH_CHILD(i, COUNT_UAC2_AS_ENDPOINT_BUFFERS)
@@ -88,6 +88,7 @@ struct uac2_ctx {
 	atomic_t as_queued;
 	atomic_t as_double;
 	uint32_t fb_queued;
+	uint32_t fb_double;
 };
 
 /* UAC2 device constant data */
@@ -441,7 +442,11 @@ static void write_explicit_feedback(struct usbd_class_data *const c_data,
 		LOG_ERR("Failed to enqueue net_buf for 0x%02x", ep);
 		net_buf_unref(buf);
 	} else {
-		ctx->fb_queued |= BIT(as_idx);
+		if (ctx->fb_queued & BIT(as_idx)) {
+			ctx->fb_double |= BIT(as_idx);
+		} else {
+			ctx->fb_queued |= BIT(as_idx);
+		}
 	}
 }
 
@@ -813,7 +818,17 @@ static int uac2_request(struct usbd_class_data *const c_data, struct net_buf *bu
 	terminal = cfg->as_terminals[as_idx];
 
 	if (is_feedback) {
-		ctx->fb_queued &= ~BIT(as_idx);
+		bool clear_double = buf->frags;
+
+		if (ctx->fb_queued & BIT(as_idx)) {
+			ctx->fb_queued &= ~BIT(as_idx);
+		} else {
+			clear_double = true;
+		}
+
+		if (clear_double) {
+			ctx->fb_double &= ~BIT(as_idx);
+		}
 	} else if (!atomic_test_and_clear_bit(&ctx->as_queued, as_idx) || buf->frags) {
 		atomic_clear_bit(&ctx->as_double, as_idx);
 	}
@@ -880,7 +895,7 @@ static void uac2_sof(struct usbd_class_data *const c_data)
 		 * for now to allow faster recovery (i.e. reduce workload to be
 		 * done during this frame).
 		 */
-		if (ctx->fb_queued & BIT(as_idx)) {
+		if (ctx->fb_queued & ctx->fb_double & BIT(as_idx)) {
 			continue;
 		}