netdev - Re: [PATCH] Add Support for Freescale FlexCAN CAN controller

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Message-ID: <4A6D7C7E.9050703@grandegger.com>
Date:	Mon, 27 Jul 2009 12:07:58 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
CC:	Socketcan-core@...ts.berlios.de,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] Add Support for Freescale FlexCAN CAN controller

Oliver Hartkopp wrote:
> Wolfgang Grandegger wrote:
>> Sascha Hauer wrote:
>>> On Fri, Jul 24, 2009 at 04:55:02PM +0200, Wolfgang Grandegger wrote:
> 
> 
>> [...]
>>>>> +	kfree_skb(skb);
>>>> Support for echo skb using can_put/get_echo_skb() is missing. It should
>>>> not be a big deal to add it.
>>> In fact it's not missing, but the hardware is configured to receive its
>>> own packets, so this isn't needed.
>> But the user may disable IFF_ECHO, which should be handled somehow.
> 
> Really?
> 
> IMO IFF_ECHO indicates the capability of the network driver to perform the MAC
> layer frame echo on driver level.
> 
> Only when you have a CAN driver that does not have this capability (the 'bad'
> non default case) this flag is cleared.
> 
> There is no need to provide a mode that can switch this functionality 'on' and
> 'off'. IFF_ECHO is just an indication provided by the driver.
> 
> When the FlexCAN controller can 'receive' a sent frame, so that it reflects
> the correct message order on the bus, this is perfect.
> 
> In this case Sascha should set the IFF_ECHO flag and he's done.

I thought the user can toggle the IFF_ECHO flag with the "ip" utility,
but obviously I'm wrong.

Wolfgang.
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