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

Marc Kleine-Budde
2021-08-04T09:45:25Z

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On 25.07.2021 18:11:50, Dario Binacchi wrote:
> 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
> @@ -200,6 +200,7 @@ struct c_can_priv {
> atomic_t sie_pending;
> unsigned long tx_dir;
> int last_status;
> + spinlock_t tx_lock;

What does the spin lock protect?

> struct c_can_tx_ring tx;
> u16 (*read_reg)(const struct c_can_priv *priv, enum reg index);
> void (*write_reg)(const struct c_can_priv *priv, enum reg index, u16 val);
> @@ -236,4 +237,9 @@ static inline u8 c_can_get_tx_tail(const struct c_can_tx_ring *ring)
> return ring->tail & (ring->obj_num - 1);
> }
>
> +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;
> -}
> -
> static bool c_can_tx_busy(const struct c_can_priv *priv,
> const struct c_can_tx_ring *tx_ring)
> {
> @@ -470,7 +456,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
> struct can_frame *frame = (struct can_frame *)skb->data;
> struct c_can_priv *priv = netdev_priv(dev);
> struct c_can_tx_ring *tx_ring = &priv->tx;
> - u32 idx, obj;
> + u32 idx, obj, cmd = IF_COMM_TX;
>
> if (can_dropped_invalid_skb(dev, skb))
> return NETDEV_TX_OK;
> @@ -483,7 +469,11 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
> if (c_can_get_tx_free(tx_ring) == 0)
> netif_stop_queue(dev);
>
> - obj = idx + priv->msg_obj_tx_first;
> + spin_lock_bh(&priv->tx_lock);

What does the spin_lock protect? The ndo_start_xmit function is properly
serialized by the networking core.

Otherwise the patch looks good!

Marc

--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
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