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

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Date:   Wed, 4 Aug 2021 11:45:15 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Dario Binacchi <dariobin@...ero.it>
Cc:     linux-kernel@...r.kernel.org,
        Gianluca Falavigna <gianluca.falavigna@...ind.it>,
        Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RESEND PATCH 4/4] can: c_can: cache frames to operate as a true
 FIFO

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  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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