Re: [PATCH v3 2/5] can: kvaser_usb: do not increase tx statistics when sending error message frames

[Jimmy Assarsson <extja@kvaser.com>]

On 2021-11-28 13:37, Vincent Mailhol wrote:
> The CAN error message frames (i.e. error skb) are an interface
> specific to socket CAN. The payload of the CAN error message frames
> does not correspond to any actual data sent on the wire. Only an error
> flag and a delimiter are transmitted when an error occurs (c.f. ISO
> 11898-1 section 10.4.4.2 "Error flag").
> 
> For this reason, it makes no sense to increment the tx_packets and
> tx_bytes fields of struct net_device_stats when sending an error
> message frame because no actual payload will be transmitted on the
> wire.
> 
> N.B. Sending error message frames is a very specific feature which, at
> the moment, is only supported by the Kvaser Hydra hardware. Please
> refer to [1] for more details on the topic.
> 
> [1] https://lore.kernel.org/linux-can/CAMZ6RqK0rTNg3u3mBpZOoY51jLZ-et-J01tY6-+mWsM4meVw-A@mail.gmail.com/t/#u
> 
> CC: Jimmy Assarsson <extja@kvaser.com>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

Hi Vincent!

Thanks for the patch.
There are flags in the TX ACK package, which makes it possible to
determine if it was an error frame or not. So we don't need to get
the original CAN frame to determine this.
I suggest the following change:

---
  .../net/can/usb/kvaser_usb/kvaser_usb_hydra.c | 25 ++++++++++++-------
  1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c 
b/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
index 3398da323126..01b076f04e26 100644
--- a/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
+++ b/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
@@ -295,6 +295,7 @@ struct kvaser_cmd {
  #define KVASER_USB_HYDRA_CF_FLAG_OVERRUN	BIT(1)
  #define KVASER_USB_HYDRA_CF_FLAG_REMOTE_FRAME	BIT(4)
  #define KVASER_USB_HYDRA_CF_FLAG_EXTENDED_ID	BIT(5)
+#define KVASER_USB_HYDRA_CF_FLAG_TX_ACK 	BIT(6)
  /* CAN frame flags. Used in ext_rx_can and ext_tx_can */
  #define KVASER_USB_HYDRA_CF_FLAG_OSM_NACK	BIT(12)
  #define KVASER_USB_HYDRA_CF_FLAG_ABL		BIT(13)
@@ -1112,7 +1113,9 @@ static void kvaser_usb_hydra_tx_acknowledge(const 
struct kvaser_usb *dev,
  	struct kvaser_usb_tx_urb_context *context;
  	struct kvaser_usb_net_priv *priv;
  	unsigned long irq_flags;
+	unsigned int len;
  	bool one_shot_fail = false;
+	bool is_err_frame = false;
  	u16 transid = kvaser_usb_hydra_get_cmd_transid(cmd);

  	priv = kvaser_usb_hydra_net_priv_from_cmd(dev, cmd);
@@ -1131,24 +1134,28 @@ static void 
kvaser_usb_hydra_tx_acknowledge(const struct kvaser_usb *dev,
  			kvaser_usb_hydra_one_shot_fail(priv, cmd_ext);
  			one_shot_fail = true;
  		}
-	}
-
-	context = &priv->tx_contexts[transid % dev->max_tx_urbs];
-	if (!one_shot_fail) {
-		struct net_device_stats *stats = &priv->netdev->stats;
-
-		stats->tx_packets++;
-		stats->tx_bytes += can_fd_dlc2len(context->dlc);
+		if (flags & KVASER_USB_HYDRA_CF_FLAG_TX_ACK &&
+		    flags & KVASER_USB_HYDRA_CF_FLAG_ERROR_FRAME)
+			 is_err_frame = true;
  	}

  	spin_lock_irqsave(&priv->tx_contexts_lock, irq_flags);

-	can_get_echo_skb(priv->netdev, context->echo_index, NULL);
+	context = &priv->tx_contexts[transid % dev->max_tx_urbs];
+	len = can_get_echo_skb(priv->netdev, context->echo_index, NULL);
+
  	context->echo_index = dev->max_tx_urbs;
  	--priv->active_tx_contexts;
  	netif_wake_queue(priv->netdev);

  	spin_unlock_irqrestore(&priv->tx_contexts_lock, irq_flags);
+
+	if (!one_shot_fail && !is_err_frame) {
+		struct net_device_stats *stats = &priv->netdev->stats;
+
+		stats->tx_packets++;
+		stats->tx_bytes += len;
+	}
  }

  static void kvaser_usb_hydra_rx_msg_std(const struct kvaser_usb *dev,
-- 
2.31.1

Best regards,
jimmy


> ---
>   .../net/can/usb/kvaser_usb/kvaser_usb_hydra.c | 22 +++++++++++++------
>   1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c b/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
> index 3398da323126..32fe352dabeb 100644
> --- a/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
> +++ b/drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c
> @@ -1111,8 +1111,10 @@ static void kvaser_usb_hydra_tx_acknowledge(const struct kvaser_usb *dev,
>   {
>   	struct kvaser_usb_tx_urb_context *context;
>   	struct kvaser_usb_net_priv *priv;
> +	struct can_frame *cf;
>   	unsigned long irq_flags;
> -	bool one_shot_fail = false;
> +	int len;
> +	bool one_shot_fail = false, is_err_frame = false;
>   	u16 transid = kvaser_usb_hydra_get_cmd_transid(cmd);
>   
>   	priv = kvaser_usb_hydra_net_priv_from_cmd(dev, cmd);
> @@ -1134,21 +1136,27 @@ static void kvaser_usb_hydra_tx_acknowledge(const struct kvaser_usb *dev,
>   	}
>   
>   	context = &priv->tx_contexts[transid % dev->max_tx_urbs];
> -	if (!one_shot_fail) {
> -		struct net_device_stats *stats = &priv->netdev->stats;
> -
> -		stats->tx_packets++;
> -		stats->tx_bytes += can_fd_dlc2len(context->dlc);
> -	}
> +	len = context->dlc;
>   
>   	spin_lock_irqsave(&priv->tx_contexts_lock, irq_flags);
>   
> +	cf = (struct can_frame *)priv->can.echo_skb[context->echo_index]->data;
> +	if (cf)
> +		is_err_frame = !!(cf->can_id & CAN_RTR_FLAG);
> +
>   	can_get_echo_skb(priv->netdev, context->echo_index, NULL);
>   	context->echo_index = dev->max_tx_urbs;
>   	--priv->active_tx_contexts;
>   	netif_wake_queue(priv->netdev);
>   
>   	spin_unlock_irqrestore(&priv->tx_contexts_lock, irq_flags);
> +
> +	if (!one_shot_fail && !is_err_frame) {
> +		struct net_device_stats *stats = &priv->netdev->stats;
> +
> +		stats->tx_packets++;
> +		stats->tx_bytes += len;
> +	}
>   }
>   
>   static void kvaser_usb_hydra_rx_msg_std(const struct kvaser_usb *dev,
>