On Sun. 11 Sept. 2022 at 21:11, Oliver Hartkopp <socketcan@xxxxxxxxxxxx> wrote: > Hi Vincent, > > On 11.09.22 09:50, Vincent Mailhol wrote: > > On Thu. 8 Sep. 2022 at 16:24, Oliver Hartkopp <socketcan@xxxxxxxxxxxx> wrote: > (..) > > >>> The CAN-ID was (due to its arbitration nature) always also a priority > >>> field. > > > > The CAN-(FD) ID holds two roles: priority and ID. For CAN XL, it is > > only ID. > > Typo? It is only the priority ;-) Yes, typo ^^; > > While I agree that both have the priority attributes, my > > concerns are on the semantics. The type is canid_t, not canprio_t. I > > just want to point that it is weird to had ID in the type when that > > field doesn't have an ID property anymore. > > CAN XL moves away from the two roles combined in the CAN(FD) Identifier. > The main focus is on arbitration now (CAN XL is like CAN arbitration > with Ethernet data). > > But in the end the CAN bitstream at the beginning of the frame including > the arbitration is completely identical for all CAN variants. > > Even when this arbitration field is now named priority for CAN XL it is > still the exact mechanism of the CAN identifier (what we introduces > canid_t for). > > Therefore having canid_t for can_id and prio seems appropriate. I guess you have a better insight. Thanks for the details. > >>> So nothing changed here. There is no RTR and no 29-bit priority anymore > >>> now. The RTR flag has already been disabled for CAN FD (see presentation > >>> at the end of this mail). > >>> > >>> Therefore it makes sense to handle the SFF 11-bit prio analogue to the > >>> former CAN-ID - and also use canid_t to simply keep the entire CAN > >>> filter handling in af_can.c ! > > > > This is a good argument to keep using the canid_t. If we make it a > > u16, we lose the alignment (unless we add dirty endianness > > preprocessing macros). > > Yep. > > (..) > > >>> Btw. I uploaded a presentation which shows the way from classical CAN to > >>> CAN XL which might depict some relations of the bits in a clearer way: > >>> > >>> https://github.com/linux-can/can-doc/blob/master/presentations/CAN-XL-Intro.pdf > > > > Thanks. With the Bosch PDF now returning error 404, I suggest > > replacing the link in the cover letter with your link (or the CIA > > knowledge page). > > Ok, will do. Yours sincerely, Vincent Mailhol
