can: m_can: Batch FIFO writes during CAN transmit

Give FIFO writes the same treatment as reads to avoid fixed costs of
individual transfers on a slow bus (e.g., tcan4x5x).

Link: https://lore.kernel.org/r/20210817050853.14875-4-matt@bitbashing.io
Signed-off-by: Matt Kline <matt@bitbashing.io>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index fbd32b4..2470c47 100644 (file)
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -279,7 +279,7 @@ enum m_can_reg {
 /* Message RAM Elements */
 #define M_CAN_FIFO_ID          0x0
 #define M_CAN_FIFO_DLC         0x4
-#define M_CAN_FIFO_DATA(n)     (0x8 + ((n) << 2))
+#define M_CAN_FIFO_DATA                0x8
 
 /* Rx Buffer Element */
 /* R0 */
@@ -514,7 +514,7 @@ static int m_can_read_fifo(struct net_device *dev, u32 rxfs)
                if (fifo_header.dlc & RX_BUF_BRS)
                        cf->flags |= CANFD_BRS;
 
-               err = m_can_fifo_read(cdev, fgi, M_CAN_FIFO_DATA(0),
+               err = m_can_fifo_read(cdev, fgi, M_CAN_FIFO_DATA,
                                      cf->data, DIV_ROUND_UP(cf->len, 4));
                if (err)
                        goto out_fail;
@@ -1588,8 +1588,9 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
        struct canfd_frame *cf = (struct canfd_frame *)cdev->tx_skb->data;
        struct net_device *dev = cdev->net;
        struct sk_buff *skb = cdev->tx_skb;
-       u32 id, dlc, cccr, fdflags;
-       int i, err;
+       struct id_and_dlc fifo_header;
+       u32 cccr, fdflags;
+       int err;
        int putidx;
 
        cdev->tx_skb = NULL;
@@ -1597,34 +1598,30 @@ 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) {
-               id = cf->can_id & CAN_EFF_MASK;
-               id |= TX_BUF_XTD;
+               fifo_header.id = cf->can_id & CAN_EFF_MASK;
+               fifo_header.id |= TX_BUF_XTD;
        } else {
-               id = ((cf->can_id & CAN_SFF_MASK) << 18);
+               fifo_header.id = ((cf->can_id & CAN_SFF_MASK) << 18);
        }
 
        if (cf->can_id & CAN_RTR_FLAG)
-               id |= TX_BUF_RTR;
+               fifo_header.id |= TX_BUF_RTR;
 
        if (cdev->version == 30) {
                netif_stop_queue(dev);
 
-               /* message ram configuration */
-               err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_ID, &id, 1);
+               fifo_header.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);
                if (err)
                        goto out_fail;
 
-               dlc = can_fd_len2dlc(cf->len) << 16;
-               err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_DLC, &dlc, 1);
+               err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_DATA,
+                                      cf->data, DIV_ROUND_UP(cf->len, 4));
                if (err)
                        goto out_fail;
 
-               for (i = 0; i < cf->len; i += 4) {
-                       err = m_can_fifo_write(cdev, 0, M_CAN_FIFO_DATA(i / 4), cf->data + i, 1);
-                       if (err)
-                               goto out_fail;
-               }
-
                can_put_echo_skb(skb, dev, 0, 0);
 
                if (cdev->can.ctrlmode & CAN_CTRLMODE_FD) {
@@ -1667,10 +1664,11 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
                /* get put index for frame */
                putidx = FIELD_GET(TXFQS_TFQPI_MASK,
                                   m_can_read(cdev, M_CAN_TXFQS));
-               /* Write ID Field to FIFO Element */
-               err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID, &id, 1);
-               if (err)
-                       goto out_fail;
+
+               /* Construct DLC Field, with CAN-FD configuration.
+                * Use the put index of the fifo as the message marker,
+                * used in the TX interrupt for sending the correct echo frame.
+                */
 
                /* get CAN FD configuration of frame */
                fdflags = 0;
@@ -1680,24 +1678,17 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
                                fdflags |= TX_BUF_BRS;
                }
 
-               /* Construct DLC Field. Also contains CAN-FD configuration
-                * use put index of fifo as message marker
-                * it is used in TX interrupt for
-                * sending the correct echo frame
-                */
-               dlc = FIELD_PREP(TX_BUF_MM_MASK, putidx) |
+               fifo_header.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_DLC, &dlc, 1);
+               err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID, &fifo_header, 2);
                if (err)
                        goto out_fail;
 
-               for (i = 0; i < cf->len; i += 4) {
-                       err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_DATA(i / 4),
-                                              cf->data + i, 1);
-                       if (err)
-                               goto out_fail;
-               }
+               err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_DATA,
+                                      cf->data, DIV_ROUND_UP(cf->len, 4));
+               if (err)
+                       goto out_fail;
 
                /* Push loopback echo.
                 * Will be looped back on TX interrupt based on message marker