On Fri. 15 Jan 2021 at 23:47, Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> wrote: > On 1/15/21 2:59 PM, Vincent MAILHOL wrote: > >>>>> I would just like your opinion on one topic: the tdco is specific > >>>>> to CAN FD. If we add it, we have two choices: > >>>>> 1. put it in struct can_bittiming: that will mean that we will > >>>>> have an unused field for classical CAN (field bittiming of > >>>>> struct can_priv). > >>>>> 2. put it in struct can_priv (but outside of struct > >>>>> can_bittiming): no unused field but less pretty. > >>>> > >>>> 3. Deprecate struct can_bittiming as the user space interface > >>>> and transfer each member individually via netlink. Extend > >>>> the kernel-only can_bittiming by the tdc related > >>>> parameters, and add these to the new netlink interface. > > > > Wow, didn't see that third option coming! > > > > By "extend the kernel-only can_bittiming by the tdc related > > parameters" do you mean to still use a single struct > > can_bittiming for classical CAN and CAN FD with the tdc > > parameters in both (a bit like what I suggested in 1.)? > > Let's put it this way, we need 3. in order to implement 1. As we need a stable > userspace ABI. I was not familiar enough with the netlink interface to foresee all those dependencies but thanks to your explanations, now everything starts to make sense. > Option 4: > We can introduce a struct can_bitiming_fd with the first member being the struct > can_bitiming and add tdc related variables after that. This way we can use the > same function to calculate the bit timing on both CAN and CAN-FD. While option 3 is slightly easier, my preference will go to option 4. > What about future developments? > > Does anyone have a clue about CAN-XL? Will we ever see real HW? Recent news would suggest that CiA will release the CAN XL specification this year: https://www.can-cia.org/news/cia-in-action/view/a-bright-future-for-can/2021/1/2/ > Or will > 10Base-T1 and 100Base-T1 take the market? My guts tell me that 100Base-T1 will take the market for autonomous driving (camera, Lidar...) and that CAN(-FD) has still a bright future for safety critical domains, at least in the next decade. Will CAN XL find its place or will it meet the same destiny as flexray? I do not know. But once the specification and the first hardware are out, we would probably start to implement it in Socket CAN before knowing if it will win the market :) Nonetheless, if we follow your idea of transferring each member individually via netlink, then we will have enough flexibility to adjust the new kernel only can_bitiming structures to our liking. > There are also these new transceivers in development that should be better > suited for "special" bus setups. Do these require additional bittiming parameters? Yours sincerely, Vincent > Marc > > -- > Pengutronix e.K. | Marc Kleine-Budde | > Embedded Linux | https://www.pengutronix.de | > Vertretung West/Dortmund | Phone: +49-231-2826-924 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | >
