spi/rockchip: fix bug that cause the failure to read data in DMA mode

In my test on RK3288-pinky board, if spi is enabled, it will begin to
read data from slave regardless of whether the DMA is ready. So we
need prepare DMA before spi is enable.
Signed-off-by: Addy Ke <addy.ke@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

drivers/spi/spi-rockchip.c

@@ -415,7 +415,7 @@ static void rockchip_spi_dma_txcb(void *data)
 	spin_unlock_irqrestore(&rs->lock, flags);
 }
 
-static int rockchip_spi_dma_transfer(struct rockchip_spi *rs)
+static void rockchip_spi_prepare_dma(struct rockchip_spi *rs)
 {
 	unsigned long flags;
 	struct dma_slave_config rxconf, txconf;
@@ -474,8 +474,6 @@ static int rockchip_spi_dma_transfer(struct rockchip_spi *rs)
 		dmaengine_submit(txdesc);
 		dma_async_issue_pending(rs->dma_tx.ch);
 	}
-
-	return 1;
 }
 
 static void rockchip_spi_config(struct rockchip_spi *rs)
@@ -556,16 +554,17 @@ static int rockchip_spi_transfer_one(
 	else if (rs->rx)
 		rs->tmode = CR0_XFM_RO;
 
-	if (master->can_dma && master->can_dma(master, spi, xfer))
+	/* we need prepare dma before spi was enabled */
+	if (master->can_dma && master->can_dma(master, spi, xfer)) {
 		rs->use_dma = 1;
-	else
+		rockchip_spi_prepare_dma(rs);
+	} else {
 		rs->use_dma = 0;
+	}
 
 	rockchip_spi_config(rs);
 
-	if (rs->use_dma)
-		ret = rockchip_spi_dma_transfer(rs);
-	else
+	if (!rs->use_dma)
 		ret = rockchip_spi_pio_transfer(rs);
 
 	return ret;