dmaengine: freescale: add and export fsl_dma_external_start()

The freescale driver uses custom device control FSLDMA_EXTERNAL_START to
put the controller in external start mode.
Since we are planning to deprecate the device control, move this to exported
API. Subsequent patches will remove the FSLDMA_EXTERNAL_START

Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/fsldma.c

@@ -36,7 +36,7 @@
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
-
+#include <linux/fsldma.h>
 #include "dmaengine.h"
 #include "fsldma.h"
 
@@ -367,6 +367,20 @@ static void fsl_chan_toggle_ext_start(struct fsldma_chan *chan, int enable)
 		chan->feature &= ~FSL_DMA_CHAN_START_EXT;
 }
 
+int fsl_dma_external_start(struct dma_chan *dchan, int enable)
+{
+	struct fsldma_chan *chan;
+
+	if (!dchan)
+		return -EINVAL;
+
+	chan = to_fsl_chan(dchan);
+
+	fsl_chan_toggle_ext_start(chan, enable);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fsl_dma_external_start);
+
 static void append_ld_queue(struct fsldma_chan *chan, struct fsl_desc_sw *desc)
 {
 	struct fsl_desc_sw *tail = to_fsl_desc(chan->ld_pending.prev);

include/linux/fsldma.h

@@ -0,0 +1,13 @@
+/*
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef FSL_DMA_H
+#define FSL_DMA_H
+/* fsl dma API for enxternal start */
+int fsl_dma_external_start(struct dma_chan *dchan, int enable);
+
+#endif