About timestamping and can-utils

[Stephane Grosjean <s.grosjean@peak-system.com>]

Hi linux-can team,

I've got one question about how timestamping is done now in linux-can, 
regarding to HW timestamps.

In the early ages (~v3.4), the CAN hardware driver could set the 
timestamp of an skb by itself and push it with the received CAN frame, 
so that the application could get it using SO_TIMESTAMP socket option, 
right?
Now, this "hardware" timestamp is to be copied into "hwstamp" field of 
the "skb_hwtstamps(skb)" area.

But how does user application manage to get this hardware timestamp on 
its side? AFAIK, the "candump" can-utils utility always reads and 
displays the "network" timestamp (that is, always uses SO_TIMESTAMP 
socket option). I had a quick look to the Kernel sources and tried to 
find the links between things but it's not very clear to me: first idea 
I tested was to set the SO_TIMESTAMPING socket option, but candump never 
received any hw timestamp in the control messages he reads from the CAN 
socket...

Any help would be appreciated.

Regards,

Stéphane
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