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

[Marc Kleine-Budde <mkl@pengutronix.de>]

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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.

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. What about
the RX path? We can just use the new 64 byte CAN frames and have to
tweak the CAN_RAW if the read from the userspace is too small.

regards, Marc

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