dmaengine: sh: rcar-dmac: Add dma_pause operation

This patch adds dma_pause operation. This patch is based on
Muhammad Hamza Farooq's patch.

After this patch applied, an issue that the sh-sci driver with
high baud rate might cause data lost disappeared because the DMAC
is possible to transmit between [1] and [2] below, and then
the residue of [1] is not true:

In rx_timer_fn() of the sh-sci.c:
	dmaengine_pause();
	...
	dmaengine_tx_status();		/* [1] */
	...
	dmaengine_terminate_all();	/* [2] */
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/sh/rcar-dmac.c

@@ -834,6 +834,17 @@ static void rcar_dmac_stop_all_chan(struct rcar_dmac *dmac)
 	}
 }
 
+static int rcar_dmac_chan_pause(struct dma_chan *chan)
+{
+	unsigned long flags;
+	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
+
+	spin_lock_irqsave(&rchan->lock, flags);
+	rcar_dmac_clear_chcr_de(rchan);
+	spin_unlock_irqrestore(&rchan->lock, flags);
+
+	return 0;
+}
 
 /* -----------------------------------------------------------------------------
  * Descriptors preparation
@@ -1864,6 +1875,7 @@ static int rcar_dmac_probe(struct platform_device *pdev)
 	engine->device_prep_slave_sg		= rcar_dmac_prep_slave_sg;
 	engine->device_prep_dma_cyclic		= rcar_dmac_prep_dma_cyclic;
 	engine->device_config			= rcar_dmac_device_config;
+	engine->device_pause			= rcar_dmac_chan_pause;
 	engine->device_terminate_all		= rcar_dmac_chan_terminate_all;
 	engine->device_tx_status		= rcar_dmac_tx_status;
 	engine->device_issue_pending		= rcar_dmac_issue_pending;