On Wed, Jan 25, 2023 at 08:50:49PM +0100, Markus Schneider-Pargmann wrote:
> Combine header and data before writing to the transmit fifo to reduce
> the overhead for peripheral chips.
>
> Signed-off-by: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx>
> ---
> drivers/net/can/m_can/m_can.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index 78f6ed744c36..440bc0536951 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -1681,6 +1681,7 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
> m_can_write(cdev, M_CAN_TXBAR, 0x1);
> /* End of xmit function for version 3.0.x */
> } else {
> + char buf[TXB_ELEMENT_SIZE];
> /* Transmit routine for version >= v3.1.x */
>
> txfqs = m_can_read(cdev, M_CAN_TXFQS);
> @@ -1720,12 +1721,11 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
> 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_ID, &fifo_header, 2);
> - if (err)
> - goto out_fail;
> + memcpy(buf, &fifo_header, 8);
> + memcpy(&buf[8], &cf->data, cf->len);
>
> - err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_DATA,
> - cf->data, DIV_ROUND_UP(cf->len, 4));
> + err = m_can_fifo_write(cdev, putidx, M_CAN_FIFO_ID,
> + buf, 8 + DIV_ROUND_UP(cf->len, 4));
Perhaps I am missing something here, but my reading is that:
- 8 is a length in bytes
- the 5th argument to m_can_fifo_write is the val_count parameter,
whose unit is 4-byte long values.
By this logic, perhaps the correct value for this argument is:
DIV_ROUND_UP(8 + cf->len, 4)
Also:
- If cf->len is not a multiple of 4, is there a possibility
that uninitialised trailing data in buf will be used
indirectly by m_can_fifo_write()?
> if (err)
> goto out_fail;
>
> --
> 2.39.0
>
