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Commit 07c7b6f6 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Marc Kleine-Budde
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can: c_can: Fix the lost message handling 



The lost message handling is broken in several ways.

1) Clearing the message lost flag is done by writing 0 to the
   message control register of the object.

   #define IF_MCONT_CLR_MSGLST    (0 << 14)

   That clears the object buffer configuration in the worst case,
   which results in a loss of the EOB flag. That leaves the FIFO chain
   without a limit and causes a complete lockup of the HW

2) In case that the error skb allocation fails, the code happily
   claims that it handed down a packet. Just an accounting bug, but ....

3) The code adds a lot of pointless overhead to that error case, where
   we need to get stuff done as fast as possible to avoid more packet
   loss.

   - printk an annoying error message
   - reread the object buffer for nothing

Fix is simple again:

  - Use the already known MSGCTRL content and only clear the MSGLST bit
  - Fix the buffer accounting by adding a proper return code
  - Remove the pointless operations

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 64f08f2f

drivers/net/can/c_can/c_can.c

+15 −16
Original line number Diff line number Diff line
@@ -122,7 +122,6 @@ 
/* IFx message control */

#define IF_MCONT_NEWDAT		BIT(15)

#define IF_MCONT_MSGLST		BIT(14)

#define IF_MCONT_CLR_MSGLST	(0 << 14)

#define IF_MCONT_INTPND		BIT(13)

#define IF_MCONT_UMASK		BIT(12)

#define IF_MCONT_TXIE		BIT(11)
@@ -411,27 +410,22 @@ static inline void c_can_activate_rx_msg_obj(struct net_device *dev, 
	c_can_object_put(dev, iface, obj, IF_COMM_CONTROL);

}



static void c_can_handle_lost_msg_obj(struct net_device *dev,

					int iface, int objno)

static int c_can_handle_lost_msg_obj(struct net_device *dev,

				     int iface, int objno, u32 ctrl)

{

	struct c_can_priv *priv = netdev_priv(dev);

	struct net_device_stats *stats = &dev->stats;

	struct sk_buff *skb;

	struct c_can_priv *priv = netdev_priv(dev);

	struct can_frame *frame;

	struct sk_buff *skb;



	netdev_err(dev, "msg lost in buffer %d\n", objno);



	c_can_object_get(dev, iface, objno, IF_COMM_ALL & ~IF_COMM_TXRQST);



	priv->write_reg(priv, C_CAN_IFACE(MSGCTRL_REG, iface),

			IF_MCONT_CLR_MSGLST);



	ctrl &= ~(IF_MCONT_MSGLST | IF_MCONT_INTPND | IF_MCONT_NEWDAT);

	priv->write_reg(priv, C_CAN_IFACE(MSGCTRL_REG, iface), ctrl);

	c_can_object_put(dev, iface, objno, IF_COMM_CONTROL);



	/* create an error msg */

	skb = alloc_can_err_skb(dev, &frame);

	if (unlikely(!skb))

		return;

		return 0;



	frame->can_id |= CAN_ERR_CRTL;

	frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
@@ -439,6 +433,7 @@ static void c_can_handle_lost_msg_obj(struct net_device *dev, 
	stats->rx_over_errors++;



	netif_receive_skb(skb);

	return 1;

}



static int c_can_read_msg_object(struct net_device *dev, int iface, int ctrl)
@@ -910,9 +905,13 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota) 
					C_CAN_IFACE(MSGCTRL_REG, IF_RX));



			if (msg_ctrl_save & IF_MCONT_MSGLST) {

				c_can_handle_lost_msg_obj(dev, IF_RX, msg_obj);

				num_rx_pkts++;

				quota--;

				int n;



				n = c_can_handle_lost_msg_obj(dev, IF_RX,

							      msg_obj,

							      msg_ctrl_save);

				num_rx_pkts += n;

				quota -=n;

				continue;

			}