On 02.11.2011 22:31, Reuben Dowle wrote:

quoted

quoted

If we change the behaviour of flexcan, I think at91 and slcan should

be changed too, because this should be handled consistently across all
drivers I would think.


At least the slcan driver does not support the correct echo of CAN
frames on
driver level at all. The slcan driver adapts CAN frames to a serial
line CAN
adapter where the feedback of successful transmission is not
guaranteed/checked within the serial data stream. Therefore the
interface flag
IFF_ECHO is not set in the slcan driver and the local echo is performed
in
af_can.c (as a workaround).

Regards,
Oliver

Thats fine for the echo behaviour, but does not really answer why the slcan
(and flexcan) driver is setting the stats for tx_packets and tx_bytes at 
different points in the transmission logic. To my mind, either we think the
packet has transmitted (along with its bytes) so we should increment both,
or we should increment neither.

In slcan.c the points of incrementing tx_bytes and tx_packets have been
adopted from slip.c where slcan.c heavily bases on.

Indeed one could argument that tx_packets could be incremented in slc_encaps
together with tx_bytes. This means that the packet is sent.

But the packet is surely sent in slcan_write_wakeup(), when tx_packets is
incremented. Unfortunately we do not have the can_dlc available at this point
anymore.

If you think it's worth the effort tx_packets++ could be integrated into
slc_encaps() to have a consistent statistic update (but you don't know whether
the packet hit the serial line entirely).

Additionally slip.c does it the same (inconsistent) way for the reasons above
and therefore i tend not to change it to stay on the current serial netdevices
behaviour (for slcan as only CAN netdevice).

Regards,
Oliver