migrate from req_ctx to msgb

We now generalize the USB communiction and abandon the 'req_ctx'
structure inherited from openpcd.  Instead we use the libosmocore 'msgb'
structure to handle incoming and outgoing USB tranfers.  We also use
linuxlist-based msgb-queues for each endpoint.

firmware/libcommon/source/usb_buf.c

@@ -0,0 +1,76 @@
+#include "board.h"
+#include "trace.h"
+#include "usb_buf.h"
+
+#include "osmocom/core/linuxlist.h"
+#include "osmocom/core/msgb.h"
+#include <errno.h>
+
+#define USB_ALLOC_SIZE	280
+
+static struct usb_buffered_ep usb_buffered_ep[BOARD_USB_NUMENDPOINTS];
+
+struct usb_buffered_ep *usb_get_buf_ep(uint8_t ep)
+{
+	if (ep >= ARRAY_SIZE(usb_buffered_ep))
+		return NULL;
+	return &usb_buffered_ep[ep];
+}
+
+
+/***********************************************************************
+ * User API
+ ***********************************************************************/
+
+struct llist_head *usb_get_queue(uint8_t ep)
+{
+	struct usb_buffered_ep *bep = usb_get_buf_ep(ep);
+	if (!bep)
+		return NULL;
+	return &bep->queue;
+}
+
+/* allocate a USB buffer for use with given end-point */
+struct msgb *usb_buf_alloc(uint8_t ep)
+{
+	struct msgb *msg;
+
+	msg = msgb_alloc(USB_ALLOC_SIZE, "USB");
+	if (!msg)
+		return NULL;
+	msg->dst = usb_get_buf_ep(ep);
+	return msg;
+}
+
+/* release/return the USB buffer to the pool */
+void usb_buf_free(struct msgb *msg)
+{
+	msgb_free(msg);
+}
+
+/* submit a USB buffer for transmission to host */
+int usb_buf_submit(struct msgb *msg)
+{
+	struct usb_buffered_ep *ep = msg->dst;
+
+	if (!msg->dst) {
+		TRACE_ERROR("%s: msg without dst\r\n", __func__);
+		usb_buf_free(msg);
+		return -EINVAL;
+	}
+
+	/* no need for irqsafe operation, as the usb_tx_queue is
+	 * processed only by the main loop context */
+	msgb_enqueue(&ep->queue, msg);
+	return 0;
+}
+
+void usb_buf_init(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(usb_buffered_ep); i++) {
+		struct usb_buffered_ep *ep = &usb_buffered_ep[i];
+		INIT_LLIST_HEAD(&ep->queue);
+	}
+}