Re: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true FIFO

Marc Kleine-Budde
2021-08-04T09:34:36Z

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On 25.07.2021 18:11:50, Dario Binacchi wrote:
> As reported by a comment in the c_can_start_xmit() this was not a FIFO.
> C/D_CAN controller sends out the buffers prioritized so that the lowest
> buffer number wins.
>
> What did c_can_start_xmit() do if head was less tail in the tx ring ? It
> waited until all the frames queued in the FIFO was actually transmitted
> by the controller before accepting a new CAN frame to transmit, even if
> the FIFO was not full, to ensure that the messages were transmitted in
> the order in which they were loaded.
>
> By storing the frames in the FIFO without requiring its transmission, we
> will be able to use the full size of the FIFO even in cases such as the
> one described above. The transmission interrupt will trigger their
> transmission only when all the messages previously loaded but stored in
> less priority positions of the buffers have been transmitted.
>
> Suggested-by: Gianluca Falavigna <gianluca.falavigna@inwind.it>
> Signed-off-by: Dario Binacchi <dariobin@libero.it>
>
> ---
>
> drivers/net/can/c_can/c_can.h | 6 +++++
> drivers/net/can/c_can/c_can_main.c | 42 +++++++++++++++++-------------
> 2 files changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
> index 8fe7e2138620..fc499a70b797 100644
> --- a/drivers/net/can/c_can/c_can.h
> +++ b/drivers/net/can/c_can/c_can.h
> +static inline u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
> +{
> + return ring->obj_num - (ring->head - ring->tail);
> +}
> +
> #endif /* C_CAN_H */
> diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
> index 451ac9a9586a..4c061fef002c 100644
> --- a/drivers/net/can/c_can/c_can_main.c
> +++ b/drivers/net/can/c_can/c_can_main.c
> @@ -427,20 +427,6 @@ static void c_can_setup_receive_object(struct net_device *dev, int iface,
> c_can_object_put(dev, iface, obj, IF_COMM_RCV_SETUP);
> }
>
> -static u8 c_can_get_tx_free(const struct c_can_tx_ring *ring)
> -{
> - u8 head = c_can_get_tx_head(ring);
> - u8 tail = c_can_get_tx_tail(ring);
> -
> - /* This is not a FIFO. C/D_CAN sends out the buffers
> - * prioritized. The lowest buffer number wins.
> - */
> - if (head < tail)
> - return 0;
> -
> - return ring->obj_num - head;
> -}
> -

Can you move that change into patch 3?

Marc

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