powerpc/mpc52xx_lpbfifo: optionally defer fifo transfer start

Currently fifo transfer is started when submitting a transfer
request. Add posibility to defer the fifo transfer and start it
later by calling additional function. This change is backward
compatible, the behaviour of mpc52xx_lpbfifo_submit() is the same
for previous driver users, so there is no need to adapt them.
Signed-off-by: Anatolij Gustschin <agust@denx.de>

arch/powerpc/include/asm/mpc52xx.h

@@ -307,6 +307,7 @@ struct mpc52xx_lpbfifo_request {
 	size_t size;
 	size_t pos;	/* current position of transfer */
 	int flags;
+	int defer_xfer_start;
 
 	/* What to do when finished */
 	void (*callback)(struct mpc52xx_lpbfifo_request *);
@@ -323,6 +324,7 @@ struct mpc52xx_lpbfifo_request {
 extern int mpc52xx_lpbfifo_submit(struct mpc52xx_lpbfifo_request *req);
 extern void mpc52xx_lpbfifo_abort(struct mpc52xx_lpbfifo_request *req);
 extern void mpc52xx_lpbfifo_poll(void);
+extern int mpc52xx_lpbfifo_start_xfer(struct mpc52xx_lpbfifo_request *req);
 
 /* mpc52xx_pic.c */
 extern void mpc52xx_init_irq(void);

arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c

@@ -170,6 +170,7 @@ static void mpc52xx_lpbfifo_kick(struct mpc52xx_lpbfifo_request *req)
 	out_be32(lpbfifo.regs + LPBFIFO_REG_CONTROL, bit_fields);
 
 	/* Kick it off */
+	if (!lpbfifo.req->defer_xfer_start)
 		out_8(lpbfifo.regs + LPBFIFO_REG_PACKET_SIZE, 0x01);
 	if (dma)
 		bcom_enable(lpbfifo.bcom_cur_task);
@@ -421,6 +422,38 @@ int mpc52xx_lpbfifo_submit(struct mpc52xx_lpbfifo_request *req)
 }
 EXPORT_SYMBOL(mpc52xx_lpbfifo_submit);
 
+int mpc52xx_lpbfifo_start_xfer(struct mpc52xx_lpbfifo_request *req)
+{
+	unsigned long flags;
+
+	if (!lpbfifo.regs)
+		return -ENODEV;
+
+	spin_lock_irqsave(&lpbfifo.lock, flags);
+
+	/*
+	 * If the req pointer is already set and a transfer was
+	 * started on submit, then this transfer is in progress
+	 */
+	if (lpbfifo.req && !lpbfifo.req->defer_xfer_start) {
+		spin_unlock_irqrestore(&lpbfifo.lock, flags);
+		return -EBUSY;
+	}
+
+	/*
+	 * If the req was previously submitted but not
+	 * started, start it now
+	 */
+	if (lpbfifo.req && lpbfifo.req == req &&
+	    lpbfifo.req->defer_xfer_start) {
+		out_8(lpbfifo.regs + LPBFIFO_REG_PACKET_SIZE, 0x01);
+	}
+
+	spin_unlock_irqrestore(&lpbfifo.lock, flags);
+	return 0;
+}
+EXPORT_SYMBOL(mpc52xx_lpbfifo_start_xfer);
+
 void mpc52xx_lpbfifo_abort(struct mpc52xx_lpbfifo_request *req)
 {
 	unsigned long flags;