netdev - RE: [PATCH] flexcan: Fix CAN_RAW_RECV_OWN_MSGS and CAN_RAW

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Message-ID: <70F6AAAFDC054F41B9994A9BCD3DF64E16FAA8E0@exch01-aklnz.MARINE.NET.INT>
Date:	Thu, 3 Nov 2011 10:31:13 +1300
From:	"Reuben Dowle" <Reuben.Dowle@...ico.com>
To:	"Oliver Hartkopp" <socketcan@...tkopp.net>
Cc:	"Kurt Van Dijck" <kurt.van.dijck@....be>, <netdev@...r.kernel.org>,
	<linux-can@...r.kernel.org>
Subject: RE: [PATCH] flexcan: Fix CAN_RAW_RECV_OWN_MSGS and CAN_RAW_LOOPBACK

> >
> > 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.

Reuben