serial: sh-sci: Switch to dma_map_single() for DMA transmission

Simplify the DMA transmit code by using dma_map_single() instead of
constantly modifying the single-entry scatterlist to match what's
currently being transmitted.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sh-sci.c

@@ -109,8 +109,8 @@ struct sci_port {
 	dma_cookie_t			cookie_tx;
 	dma_cookie_t			cookie_rx[2];
 	dma_cookie_t			active_rx;
-	struct scatterlist		sg_tx;
-	unsigned int			sg_len_tx;
+	dma_addr_t			tx_dma_addr;
+	unsigned int			tx_dma_len;
 	struct scatterlist		sg_rx[2];
 	size_t				buf_len_rx;
 	struct sh_dmae_slave		param_tx;
@@ -1280,10 +1280,10 @@ static void sci_dma_tx_complete(void *arg)
 
 	spin_lock_irqsave(&port->lock, flags);
 
-	xmit->tail += sg_dma_len(&s->sg_tx);
+	xmit->tail += s->tx_dma_len;
 	xmit->tail &= UART_XMIT_SIZE - 1;
 
-	port->icount.tx += sg_dma_len(&s->sg_tx);
+	port->icount.tx += s->tx_dma_len;
 
 	async_tx_ack(s->desc_tx);
 	s->desc_tx = NULL;
@@ -1494,7 +1494,7 @@ static void work_fn_tx(struct work_struct *work)
 	struct dma_chan *chan = s->chan_tx;
 	struct uart_port *port = &s->port;
 	struct circ_buf *xmit = &port->state->xmit;
-	struct scatterlist *sg = &s->sg_tx;
+	dma_addr_t buf;
 
 	/*
 	 * DMA is idle now.
@@ -1504,19 +1504,15 @@ static void work_fn_tx(struct work_struct *work)
 	 * consistent xmit buffer state.
 	 */
 	spin_lock_irq(&port->lock);
-	sg->offset = xmit->tail & (UART_XMIT_SIZE - 1);
-	sg_dma_address(sg) = (sg_dma_address(sg) & ~(UART_XMIT_SIZE - 1)) +
-		sg->offset;
-	sg_dma_len(sg) = min_t(unsigned int,
+	buf = s->tx_dma_addr + (xmit->tail & (UART_XMIT_SIZE - 1));
+	s->tx_dma_len = min_t(unsigned int,
 		CIRC_CNT(xmit->head, xmit->tail, UART_XMIT_SIZE),
 		CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE));
 	spin_unlock_irq(&port->lock);
 
-	BUG_ON(!sg_dma_len(sg));
-
-	desc = dmaengine_prep_slave_sg(chan,
-			sg, s->sg_len_tx, DMA_MEM_TO_DEV,
-			DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	desc = dmaengine_prep_slave_single(chan, buf, s->tx_dma_len,
+					   DMA_MEM_TO_DEV,
+					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!desc) {
 		dev_warn(port->dev, "Failed preparing Tx DMA descriptor\n");
 		/* switch to PIO */
@@ -1524,7 +1520,8 @@ static void work_fn_tx(struct work_struct *work)
 		return;
 	}
 
-	dma_sync_sg_for_device(chan->device->dev, sg, 1, DMA_TO_DEVICE);
+	dma_sync_single_for_device(chan->device->dev, buf, s->tx_dma_len,
+				   DMA_TO_DEVICE);
 
 	spin_lock_irq(&port->lock);
 	s->desc_tx = desc;
@@ -1680,7 +1677,6 @@ static void sci_request_dma(struct uart_port *port)
 	struct sh_dmae_slave *param;
 	struct dma_chan *chan;
 	dma_cap_mask_t mask;
-	int nent;
 
 	dev_dbg(port->dev, "%s: port %d\n", __func__, port->line);
 
@@ -1700,27 +1696,21 @@ static void sci_request_dma(struct uart_port *port)
 	dev_dbg(port->dev, "%s: TX: got channel %p\n", __func__, chan);
 	if (chan) {
 		s->chan_tx = chan;
-		sg_init_table(&s->sg_tx, 1);
 		/* UART circular tx buffer is an aligned page. */
-		BUG_ON((uintptr_t)port->state->xmit.buf & ~PAGE_MASK);
-		sg_set_page(&s->sg_tx, virt_to_page(port->state->xmit.buf),
-			    UART_XMIT_SIZE,
-			    (uintptr_t)port->state->xmit.buf & ~PAGE_MASK);
-		nent = dma_map_sg(chan->device->dev, &s->sg_tx, 1,
-				  DMA_TO_DEVICE);
-		if (!nent) {
+		s->tx_dma_addr = dma_map_single(chan->device->dev,
+						port->state->xmit.buf,
+						UART_XMIT_SIZE,
+						DMA_TO_DEVICE);
+		if (dma_mapping_error(chan->device->dev, s->tx_dma_addr)) {
 			dev_warn(port->dev, "Failed mapping Tx DMA descriptor\n");
 			dma_release_channel(chan);
 			s->chan_tx = NULL;
 		} else {
-			dev_dbg(port->dev, "%s: mapped %d@%p to %pad\n",
-				__func__,
-				sg_dma_len(&s->sg_tx), port->state->xmit.buf,
-				&sg_dma_address(&s->sg_tx));
+			dev_dbg(port->dev, "%s: mapped %lu@%p to %pad\n",
+				__func__, UART_XMIT_SIZE,
+				port->state->xmit.buf, &s->tx_dma_addr);
 		}
 
-		s->sg_len_tx = nent;
-
 		INIT_WORK(&s->work_tx, work_fn_tx);
 	}