[nrf fromtree] usb: device_next: msc: Reduce memory usage

MSC BOT can work with just one buffer because buffer to receive CBW is
never queued at the same time as CSW. SCSI buffer needs to be multiple
of bulk endpoint wMaxPacketSize and therefore is suitable for handling
both CBW and CSW. Take advantage of this to reduce memory usage.

Signed-off-by: Tomasz Moń <[email protected]>
(cherry picked from commit 7e11bc5)

Author: tmon-nordic

subsys/usb/device_next/class/usbd_msc.c

@@ -62,8 +62,12 @@ struct CSW {
 
 #define MSC_NUM_BUFFERS UTIL_INC(IS_ENABLED(CONFIG_USBD_MSC_DOUBLE_BUFFERING))
 
+#if USBD_MAX_BULK_MPS > CONFIG_USBD_MSC_SCSI_BUFFER_SIZE
+#error "SCSI buffer must be at least USB bulk endpoint wMaxPacketSize"
+#endif
+
 UDC_BUF_POOL_DEFINE(msc_ep_pool, MSC_NUM_INSTANCES * (1 + MSC_NUM_BUFFERS),
-		    USBD_MAX_BULK_MPS, sizeof(struct udc_buf_info), NULL);
+		    0, sizeof(struct udc_buf_info), NULL);
 
 struct msc_event {
 	struct usbd_class_data *c_data;
@@ -125,22 +129,6 @@ struct msc_bot_ctx {
 	size_t scsi_bytes;
 };
 
-static struct net_buf *msc_buf_alloc(const uint8_t ep)
-{
-	struct net_buf *buf = NULL;
-	struct udc_buf_info *bi;
-
-	buf = net_buf_alloc(&msc_ep_pool, K_NO_WAIT);
-	if (!buf) {
-		return NULL;
-	}
-
-	bi = udc_get_buf_info(buf);
-	bi->ep = ep;
-
-	return buf;
-}
-
 static struct net_buf *msc_buf_alloc_data(const uint8_t ep, uint8_t *data, size_t len)
 {
 	struct net_buf *buf = NULL;
@@ -334,6 +322,7 @@ static void msc_queue_cbw(struct usbd_class_data *const c_data)
 {
 	struct msc_bot_ctx *ctx = usbd_class_get_private(c_data);
 	struct net_buf *buf;
+	uint8_t *scsi_buf;
 	uint8_t ep;
 	int ret;
 
@@ -342,9 +331,13 @@ static void msc_queue_cbw(struct usbd_class_data *const c_data)
 		return;
 	}
 
+	__ASSERT(ctx->scsi_bufs_used == 0,
+		 "CBW can only be queued when SCSI buffers are free");
+
 	LOG_DBG("Queuing OUT");
 	ep = msc_get_bulk_out(c_data);
-	buf = msc_buf_alloc(ep);
+	scsi_buf = msc_alloc_scsi_buf(ctx);
+	buf = msc_buf_alloc_data(ep, scsi_buf, USBD_MAX_BULK_MPS);
 
 	/* The pool is large enough to support all allocations. Failing alloc
 	 * indicates either a memory leak or logic error.
@@ -355,6 +348,7 @@ static void msc_queue_cbw(struct usbd_class_data *const c_data)
 	if (ret) {
 		LOG_ERR("Failed to enqueue net_buf for 0x%02x", ep);
 		net_buf_unref(buf);
+		msc_free_scsi_buf(ctx, scsi_buf);
 		/* 6.6.2 Internal Device Error */
 		msc_stall_and_wait_for_recovery(ctx);
 	} else {
@@ -648,6 +642,7 @@ static void msc_handle_bulk_in(struct msc_bot_ctx *ctx,
 static void msc_send_csw(struct msc_bot_ctx *ctx)
 {
 	struct net_buf *buf;
+	uint8_t *scsi_buf;
 	uint8_t ep;
 	int ret;
 
@@ -657,20 +652,25 @@ static void msc_send_csw(struct msc_bot_ctx *ctx)
 		return;
 	}
 
+	__ASSERT(ctx->scsi_bufs_used == 0,
+		 "CSW can be sent only if SCSI buffers are free");
+
 	/* Convert dCSWDataResidue to LE, other fields are already set */
 	ctx->csw.dCSWDataResidue = sys_cpu_to_le32(ctx->csw.dCSWDataResidue);
 	ep = msc_get_bulk_in(ctx->class_node);
-	buf = msc_buf_alloc(ep);
+	scsi_buf = msc_alloc_scsi_buf(ctx);
+	memcpy(scsi_buf, &ctx->csw, sizeof(ctx->csw));
+	buf = msc_buf_alloc_data(ep, scsi_buf, sizeof(ctx->csw));
 	/* The pool is large enough to support all allocations. Failing alloc
 	 * indicates either a memory leak or logic error.
 	 */
 	__ASSERT_NO_MSG(buf);
 
-	net_buf_add_mem(buf, &ctx->csw, sizeof(ctx->csw));
 	ret = usbd_ep_enqueue(ctx->class_node, buf);
 	if (ret) {
 		LOG_ERR("Failed to enqueue net_buf for 0x%02x", ep);
 		net_buf_unref(buf);
+		msc_free_scsi_buf(ctx, scsi_buf);
 		/* 6.6.2 Internal Device Error */
 		msc_stall_and_wait_for_recovery(ctx);
 	} else {