Hi Kurt, On 06/30/2017 03:09 AM, Kurt Van Dijck wrote: >> On 06/29/2017 05:36 PM, Kurt Van Dijck wrote: >>>>>> >>>>>> mcan@0 { >>>>>> ... >>>>>> fixed-transceiver { >>>>>> max-canfd-speed = <2000> >>>>>> }; >>>>>> ... >>>>>> }; >>> >>> Since when would a transceiver support different speeds for CAN & CANFD? >> >> When I say CAN I'm referring to CAN 2.0 specification which mentioned >> speeds upto 1 Mbit/s. While CAN FD supports higher bitrates. > > linux-can is not necessarily restricted to CAN 2.0B? > >> >>> No transceivers were available, but they are now. >>> I see no datalink problem applying 2MBit for regular CAN with apropriate >>> physical layer, and CAN does not predefine the physical layer >>> (advise != define). >>> >>> IMHO, >>> fixed-transceiver { >>> max-arbitration-speed = <2000000> >>> max-data-speed = <4000000> >>> }; >>> is way better to describe the hardware. >>> Regular CAN chips would not consider max-data-speed... >> >> What is arbitration speed? > > CANFD remains similar during the arbitration phase (when the CAN id is > sent on the wire), and after that allows to switch to a higher 'data' > speed because the round-trip wire restrictions during arbitration > don't apply anymore. > >> >> Also if I understand you correctly then I agree drivers for traditional >> CAN wouldn't care about this subnode. Although it may be helpful for >> max-data-speed to become max-canfd-speed or something along those lines. >> Just so the property's purpose is clear. > > Transceivers exist that don't support 1MB either. > naming the speeds max-arbitration-speed and max-data-speed makes this > OF nodes usable for that kind of CAN 2.0 restrtications too. > > Of course, CAN 2.0 chips only consider max-arbitration-speed as that > applies to the whole wire bitstream, where as CANFD considers both. > > What I understand of your proposal is that max-arbitration-speed is > 'fixed to 1MB anyway', and that assumption has been proven not > universally applicable with CAN2.0 transceivers already. > > I found the name 'max-canfd-speed' a bit dubious as CANFD relies on > 'flexible datarate'. transceivers may not necessarily support the same > speed for both arbitration and data. > So I propose to replace it with 'max-data-speed' Thanks for the explanation. Makes sense. > > Kind regards, > Kurt > >>> >>> Kind regards, >>> Kurt >>> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-can" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html