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SubjectRe: [PATCH 02/15] can: m_can: Wakeup net queue once tx was issued
On 16.11.2022 21:52:55, Markus Schneider-Pargmann wrote:
> Currently the driver waits to wakeup the queue until the interrupt for
> the transmit event is received and acknowledged. If we want to use the
> hardware FIFO, this is too late.
>
> Instead release the queue as soon as the transmit was transferred into
> the hardware FIFO. We are then ready for the next transmit to be
> transferred.
>
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> ---
> drivers/net/can/m_can/m_can.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
> index 2c01e3f7b23f..4adf03111782 100644
> --- a/drivers/net/can/m_can/m_can.c
> +++ b/drivers/net/can/m_can/m_can.c
> @@ -1097,10 +1097,9 @@ static irqreturn_t m_can_isr(int irq, void *dev_id)
> /* New TX FIFO Element arrived */
> if (m_can_echo_tx_event(dev) != 0)
> goto out_fail;
> -
> - if (netif_queue_stopped(dev) &&
> - !m_can_tx_fifo_full(cdev))
> + if (!cdev->tx_skb && netif_queue_stopped(dev))
> netif_wake_queue(dev);

Please don't start the queue if the FIFO is still full. Is this a
gamble, that it will take long enough until the work queue runs that the
FIFO is not full anymore?

> +

Nitpick: Please don't introduce an extra newline here.

> }
> }
>
> @@ -1705,6 +1704,8 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
> if (m_can_tx_fifo_full(cdev) ||
> m_can_next_echo_skb_occupied(dev, putidx))
> netif_stop_queue(dev);
> + else if (cdev->is_peripheral && !cdev->tx_skb && netif_queue_stopped(dev))
> + netif_wake_queue(dev);

Same question as above, what happens if the FIFO is full? e.g. in case
of a slow bus or the first CAN frame in the FIFO has a low prio...

> }
>
> return NETDEV_TX_OK;
> --
> 2.38.1
>
>

Marc

--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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