netdev - Re: [PATCH RESEND] net: can: Introduce MEN 16Z192-00 CAN controller driver

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Date:	Thu, 11 Aug 2016 10:58:26 +0200
From:	Andreas Werner <andreas.werner@....de>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
CC:	Andreas Werner <andreas.werner@....de>,
	Wolfgang Grandegger <wg@...ndegger.com>, <mkl@...gutronix.de>,
	<linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <davem@...emloft.net>,
	<jthumshirn@...e.de>, <andy@...nerandy.de>,
	<michael.miehling@....de>
Subject: Re: [PATCH RESEND] net: can: Introduce MEN 16Z192-00 CAN controller
 driver

On Thu, Aug 11, 2016 at 10:45:00AM +0200, Oliver Hartkopp wrote:
> On 08/11/2016 09:14 AM, Andreas Werner wrote:
> >On Wed, Aug 10, 2016 at 10:28:45PM +0200, Oliver Hartkopp wrote:
> 
> >>Just check 'git grep IFF_ECHO'. Even grcan.c and janz-ican3.c have IFF_ECHO
> >>set - but implement it in a different way without using the provided
> >>machanism from dev.c .
> >>
> >
> >Ok I am with you.
> 
> Great :-)
> 
> >>A local loopback inside the CAN controller which is generated after
> >>successful transmit is an excellent implementation with excellent
> >>timestamps. The only problem for you is to detect the looped CAN frames and
> >>match them to the skb pointer of the outgoing frame to 'receive' the correct
> >>echo skb.
> >>
> >
> >At the moment, i think there is no way to detect those looped frames.
> >I will talk to our IC designer and discuss this issue with him. Maybe we
> >have the possibility to get a local loopback inside the CAN controller.
> >This seems to be the best way to do it.
> 
> When you still have the possibility to change the IP core I would suggest to
> create some kind of 16/32 bit value which you can pass to the CAN controller
> along with the CAN frame to be sent.
> 
> And when this frame comes back due to the loopback you can use this non-zero
> 16/32 bit value to match into a list of tx skb pointers for IFF_ECHO.
> 
> E.g. when this 16/32 bit value is zero this CAN frame obviously was received
> from another CAN node.
> 
> Just an idea.
> 

I am not sure if we have a way to change the IP but i will try to talk with
my IC designer. He will be available next week.

Your idea sounds good. I will check a few more driver to get more information
how they did the implementation.

> Regards,
> Oliver

Thanks your comments and explanations Oliver.

Regards
Andy