dma: imx-sdma: keep the callbacks invoked in the tasklet

The current code keeps the callbacks invoked from interrupt context, this
does not conform to the Documentation/dmaengine.txt.

So add tasklet support to fix this issue.
Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

drivers/dma/imx-sdma.c

@@ -271,6 +271,7 @@ struct sdma_channel {
 	enum dma_status			status;
 	unsigned int			chn_count;
 	unsigned int			chn_real_count;
+	struct tasklet_struct		tasklet;
 };
 
 #define IMX_DMA_SG_LOOP		BIT(0)
@@ -534,8 +535,10 @@ static void mxc_sdma_handle_channel_normal(struct sdma_channel *sdmac)
 		sdmac->desc.callback(sdmac->desc.callback_param);
 }
 
-static void mxc_sdma_handle_channel(struct sdma_channel *sdmac)
+static void sdma_tasklet(unsigned long data)
 {
+	struct sdma_channel *sdmac = (struct sdma_channel *) data;
+
 	complete(&sdmac->done);
 
 	/* not interested in channel 0 interrupts */
@@ -560,7 +563,7 @@ static irqreturn_t sdma_int_handler(int irq, void *dev_id)
 		int channel = fls(stat) - 1;
 		struct sdma_channel *sdmac = &sdma->channel[channel];
 
-		mxc_sdma_handle_channel(sdmac);
+		tasklet_schedule(&sdmac->tasklet);
 
 		__clear_bit(channel, &stat);
 	}
@@ -1359,6 +1362,8 @@ static int __init sdma_probe(struct platform_device *pdev)
 		dma_cookie_init(&sdmac->chan);
 		sdmac->channel = i;
 
+		tasklet_init(&sdmac->tasklet, sdma_tasklet,
+			     (unsigned long) sdmac);
 		/*
 		 * Add the channel to the DMAC list. Do not add channel 0 though
 		 * because we need it internally in the SDMA driver. This also means