i2c: rcar: wait for data empty before starting DMA

When sending with DMA, the driver transfers the first byte with PIO (as
documented). However, it started DMA right after the first byte was
written. This worked, but was not according to the datasheet which
suggests to wait until data register was empty again. Implement this.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-rcar.c

@@ -480,6 +480,10 @@ static void rcar_i2c_irq_send(struct rcar_i2c_priv *priv, u32 msr)
 	if (!(msr & MDE))
 		return;
 
+	/* Check if DMA can be enabled and take over */
+	if (priv->pos == 1 && rcar_i2c_dma(priv))
+		return;
+
 	if (priv->pos < msg->len) {
 		/*
 		 * Prepare next data to ICRXTX register.
@@ -490,13 +494,6 @@ static void rcar_i2c_irq_send(struct rcar_i2c_priv *priv, u32 msr)
 		 */
 		rcar_i2c_write(priv, ICRXTX, msg->buf[priv->pos]);
 		priv->pos++;
-
-		/*
-		 * Try to use DMA to transmit the rest of the data if
-		 * address transfer phase just finished.
-		 */
-		if (msr & MAT)
-			rcar_i2c_dma(priv);
 	} else {
 		/*
 		 * The last data was pushed to ICRXTX on _PREV_ empty irq.