Re: [RFC] can: Introducing CANFD for af_can & can-raw

[Alexander Stein <alexander.stein@systec-electronic.com>]

Am Mittwoch, 21. März 2012, 13:32:52 schrieb Marc Kleine-Budde:
> On 03/21/2012 01:08 PM, Kurt Van Dijck wrote:
> > On Wed, Mar 21, 2012 at 12:43:31PM +0100, Marc Kleine-Budde wrote:
> >> On 03/21/2012 12:05 PM, Kurt Van Dijck wrote:
> >>> Hi Sebastian,
> >>> 
> >>> On the ICC, Bosch presentend CANFD[1].
> >>> I'll share my interpretation:
> >>> * CANFD is meant as a successor of CAN.
> >>> 
> >>> * it addressess data throughput in 2 ways:
> >>>   - higher data bitrate for data using a second
> >>>   
> >>>     set of bittimings.
> >>>   
> >>>   - longer message payload (up to 64 byte).
> >>> 
> >>> * it remains very compatible to CAN, although _NOT_
> >>> 
> >>>   bus-compatible (ie. you put it on a seperate bus).
> >> 
> >> This means:
> >> You cannot have a Bus using one (or more) of the CAN-FD features with
> >> non CAN-FD compatible nodes.
> >> 
> >> From my point of view this can be translated into a new property in
> >> "can.ctrlmode_supported". A device adds "CAN_CTRLMODE_CANFD" if it
> >> supports CAN FD mode. Then it's a global setting to put the device
> >> into
> >> CAN FD mode.
> > 
> > Yep, good idea.
> > 
> >> In the TX path the stack should refuse the new 64 byte frames at all
> >> or
> >> frames with dlc > 8 byes if the device is not in CAN FD mode.
> > 
> > I did not yet do such think since I did not implement CANFD on device
> > level yet. I think can_send() is a good place to put such tricks.
> 
> Yes, for CAN_RAW, but in the driver we must extend the
> "can_dropped_invalid_skb()" function, too: drop frames with dlc >8 if
> device is not in CAN FD mode.
> 
> Further, there are only certain dlc values allowed for CAN FD. We must
> decide if the enforce these values or simply do padding with "0" somewhere.

What I understand from the proposal is that DLCs >8 are optional. So you might 
get hardware which still supports only 8 bytes. How can/should this be 
handled?

Alexnder
-- 
Dipl.-Inf. Alexander Stein

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