A valid CAN dataframe can have a data length code (DLC) of 0 .. 8 data bytes.

When reading the CAN controllers register the 4-bit value may contain values
from 0 .. 15 which may exceed the reserved space in the socket buffer!

The ISO 11898-1 Chapter 8.4.2.3 (DLC field) says that register values > 8
should be reduced to 8 without any error reporting or frame drop.

This patch introduces a new helper macro to cast a given 4-bit data length
code (dlc) to __u8 and ensure the DLC value to be max. 8 bytes.

The different handlings in the rx path of the CAN netdevice drivers are fixed.
Signed-off-by: NOliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: NWolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch makes the private functions alloc_can_skb() and
alloc_can_err_skb() of the at91_can driver public and adapts all
drivers to use these. While making the patch I realized, that
the skb's are *not* setup consistently. It's now done as shown
below:

  skb->protocol = htons(ETH_P_CAN);
  skb->pkt_type = PACKET_BROADCAST;
  skb->ip_summed = CHECKSUM_UNNECESSARY;
  *cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
  memset(*cf, 0, sizeof(struct can_frame));

The frame is zeroed out to avoid uninitialized data to be passed to
user space. Some drivers or library code did not set "pkt_type" or
"ip_summed". Also,  "__constant_htons()" should not be used for
runtime invocations, as pointed out by David Miller.
Signed-off-by: NWolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch allows the CAN controller driver to define the number of echo
skb's used for the local loopback (echo), as suggested by Kurt Van
Dijck, with the function:

  struct net_device *alloc_candev(int sizeof_priv,
                                  unsigned int echo_skb_max);

The CAN drivers have been adapted accordingly. For the ems_usb driver,
as suggested by Sebastian Haas, the number of echo skb's has been
increased to 10, which improves the transmission performance a lot.
Signed-off-by: NWolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NKurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch adds the function can_free_echo_skb to the CAN
device interface to allow upcoming drivers to release echo
skb's in case of error.
Signed-off-by: NWolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The CAN network device driver interface provides a generic interface to
setup, configure and monitor CAN network devices. It exports a set of
common data structures and functions, which all real CAN network device
drivers should use. Please have a look to the SJA1000 or MSCAN driver
to understand how to use them. The name of the module is can-dev.ko.

Furthermore, it adds a Netlink interface allowing to configure the CAN
device using the program "ip" from the iproute2 utility suite.

For further information please check "Documentation/networking/can.txt"
Signed-off-by: NWolfgang Grandegger <wg@grandegger.com>
Signed-off-by: NOliver Hartkopp <oliver.hartkopp@volkswagen.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>