can: m_can: Write transmit header and data in one transaction

Combine header and data before writing to the transmit fifo to reduce
the overhead for peripheral chips.
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/all/20240207093220.2681425-4-msp@baylibre.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -320,6 +320,12 @@ struct id_and_dlc {
 	u32 dlc;
 };
 
+struct m_can_fifo_element {
+	u32 id;
+	u32 dlc;
+	u8 data[CANFD_MAX_DLEN];
+};
+
 static inline u32 m_can_read(struct m_can_classdev *cdev, enum m_can_reg reg)
 {
 	return cdev->ops->read_reg(cdev, reg);
@@ -1637,9 +1643,10 @@ static int m_can_next_echo_skb_occupied(struct net_device *dev, int putidx)
 static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 {
 	struct canfd_frame *cf = (struct canfd_frame *)cdev->tx_skb->data;
+	u8 len_padded = DIV_ROUND_UP(cf->len, 4);
+	struct m_can_fifo_element fifo_element;
 	struct net_device *dev = cdev->net;
 	struct sk_buff *skb = cdev->tx_skb;
-	struct id_and_dlc fifo_header;
 	u32 cccr, fdflags;
 	u32 txfqs;
 	int err;
@@ -1650,27 +1657,27 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 	/* Generate ID field for TX buffer Element */
 	/* Common to all supported M_CAN versions */
 	if (cf->can_id & CAN_EFF_FLAG) {
-		fifo_header.id = cf->can_id & CAN_EFF_MASK;
-		fifo_header.id |= TX_BUF_XTD;
+		fifo_element.id = cf->can_id & CAN_EFF_MASK;
+		fifo_element.id |= TX_BUF_XTD;
 	} else {
-		fifo_header.id = ((cf->can_id & CAN_SFF_MASK) << 18);
+		fifo_element.id = ((cf->can_id & CAN_SFF_MASK) << 18);
 	}
 
 	if (cf->can_id & CAN_RTR_FLAG)
-		fifo_header.id |= TX_BUF_RTR;
+		fifo_element.id |= TX_BUF_RTR;
 
 	if (cdev->version == 30) {
 		netif_stop_queue(dev);
 
-		fifo_header.dlc = can_fd_len2dlc(cf->len) << 16;
+		fifo_element.dlc = can_fd_len2dlc(cf->len) << 16;
 
 		/* Write the frame ID, DLC, and payload to the FIFO element. */
-		err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_ID, &fifo_header, 2);
+		err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_ID, &fifo_element, 2);
 		if (err)
 			goto out_fail;
 
 		err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_DATA,
-				       cf->data, DIV_ROUND_UP(cf->len, 4));
+				       cf->data, len_padded);
 		if (err)
 			goto out_fail;
 
@@ -1732,15 +1739,15 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 				fdflags |= TX_BUF_BRS;
 		}
 
-		fifo_header.dlc = FIELD_PREP(TX_BUF_MM_MASK, putidx) |
+		fifo_element.dlc = FIELD_PREP(TX_BUF_MM_MASK, putidx) |
 			FIELD_PREP(TX_BUF_DLC_MASK, can_fd_len2dlc(cf->len)) |
 			fdflags | TX_BUF_EFC;
-		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID, &fifo_header, 2);
-		if (err)
-			goto out_fail;
 
-		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_DATA,
-				       cf->data, DIV_ROUND_UP(cf->len, 4));
+		memcpy_and_pad(fifo_element.data, CANFD_MAX_DLEN, &cf->data,
+			       cf->len, 0);
+
+		err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID,
+				       &fifo_element, 2 + len_padded);
 		if (err)
 			goto out_fail;