can: c_can: Fix tx_bytes accounting

The current SocketCAN implementation for the Bosch c_can cell doesn't
account the TX bytes correctly, because it calls
c_can_inval_msg_object() (which clears the msg ctrl register) before
reading the DLC value:

for (/* nix */; (priv->tx_next - priv->tx_echo) > 0; priv->tx_echo++) {
        msg_obj_no = get_tx_echo_msg_obj(priv);
        c_can_inval_msg_object(dev, 0, msg_obj_no);
        val = c_can_read_reg32(priv, &priv->regs->txrqst1);
        if (!(val & (1 << msg_obj_no))) {
                can_get_echo_skb(dev,
                                msg_obj_no - C_CAN_MSG_OBJ_TX_FIRST);
                stats->tx_bytes += priv->read_reg(priv,
                                &priv->regs->ifregs[0].msg_cntrl)
                                & IF_MCONT_DLC_MASK;
                stats->tx_packets++;
        }
}

So, we will always read 0 for the DLC value and "ifconfig" will report
*0* TX Bytes.

The fix is quite easy: Just move c_can_inval_msg_object() to the end of
the if() statement. So:
      * We only call c_can_inval_msg_object() if the message was
        actually transmitted
      * We read out the DLC value _before_ clearing the msg ctrl
        register

Signed-off-by: Jan Altenberg <jan@linutronix.de>
Acked-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
index d0bffb08aef5c8d65bb1478702361fd7cc3641b8..31552959aed7baa4895ac386d390b0a331abde6e 100644 (file)
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -699,7 +699,6 @@ static void c_can_do_tx(struct net_device *dev)
 
        for (/* nix */; (priv->tx_next - priv->tx_echo) > 0; priv->tx_echo++) {
                msg_obj_no = get_tx_echo_msg_obj(priv);
-               c_can_inval_msg_object(dev, 0, msg_obj_no);
                val = c_can_read_reg32(priv, &priv->regs->txrqst1);
                if (!(val & (1 << msg_obj_no))) {
                        can_get_echo_skb(dev,
@@ -708,6 +707,7 @@ static void c_can_do_tx(struct net_device *dev)
                                        &priv->regs->ifregs[0].msg_cntrl)
                                        & IF_MCONT_DLC_MASK;
                        stats->tx_packets++;
+                       c_can_inval_msg_object(dev, 0, msg_obj_no);
                }
        }