Hi Oliver, Thanks for the comments. > On 03/07/2016 09:32 AM, Ramesh Shanmugasundaram wrote: > > >>>>> + /* Ensure channel starts in FD mode */ > >>>>> + if (!(priv->can.ctrlmode & CAN_CTRLMODE_FD)) { > >>>>> + netdev_err(ndev, "enable can fd mode for channel %d\n", > ch); > >>>>> + goto fail_mode; > >>>>> + } > >>>> > >>>> What's the reason behind this check? > >>>> > >>>> A CAN FD capable CAN controller can be either configured to run as > >>>> CAN 2.0 (Classic CAN) or as CAN FD controller. > >>>> > >>>> So why are to throwing an error here and produce an initialization > >>>> failure? > >>> > >>> When this controller is configured in FD mode and used only with CAN > >>> 2.0 nodes, it still expects a DTSEG (data bitrate) configuration > >>> same as NTSEG (nominal bitrate). This check, specifically in > >>> ndo_open, ensures both are configured and will work fine with CAN > >>> 2.0 nodes > >>> (e.g.) > >>> > >>> "ip link set can0 up type can bitrate 1000000 dbitrate 1000000 fd on" > >>> > >>> If I don't have this check, a configuration like this > >>> > >>> "ip link set can0 up type can bitrate 1000000" > >>> > >>> will bring up the controller without DTSEG configured. > > What about spending some status flag or setting the data bitrate equal to > the nominal bitrate unless a data bitrate is provided? As you mentioned further down, when a user does this "ip link set can0 up type can bitrate 1000000" the intention is to put the controller in CAN 2.0 mode. Even if we use a status flag or copy the data bitrate equal to the nominal bitrate, what would it achieve? It still cannot be a CAN 2.0 node - it is a CAN FD node configured with same nominal & data bitrate. This is why I have this check in ndo_open, so that the user is aware it is a CAN FD node always and avoid misconfiguration like above with EOPNOTSUPP. > > >> > >> That should bring up the controller in CAN 2.0 mode. > > > > Yes, that's the user's intention but the manual states DTSEG still need > to be configured. In the above configuration, it will not be. > > Besides, this will not be a "pure" CAN 2.0 node (i.e.) if a frame with > length > 8 bytes is received the controller will "ACK" because in FD mode > it can receive up to 64 bytes frame. > > Oh. We probably mix something up here (CAN frame formats & bitrates). > > A CAN2.0 frame and a CAN FD frame have very different representations on > the wire! So if you see a FDF (former EDL) bit this is a CAN FD frame, > which requires two bitrates (nominal/data bitrate) where the data bitrate > has to be greater or equal the nominal bitrate. > > The fact that the data bitrate is equal the nominal/arbitration bitrate > has nothing to do with CAN2.0 then. Regarding your answer this is not even > "a pure CAN2.0" node - it still looks like a CAN FD node with equal > data/nominal bitrates. I agree. May be I mixed up my wordings but my intention is same - the controller is still an FD node & not pure CAN 2.0 node. This is why I have the check. > > The fact that a CAN FD frame has a size of 8 bytes doesn't make it a > CAN2.0 frame :-) > > > > > The controller does support a "pure" classical CAN mode with a different > set of register map itself. > > Is this a can_rcar controller register mapping then? Nope. This is a different IP compared to can_rcar. It has a different set of register map within the IP to act as a pure classical CAN 2.0 node. When I say "pure", it will pass CAN 2.0 conformance tests :-). It is worth adding this support? Do you think of a strong use case? > > > Do you think a pure CAN 2.0 mode support would be beneficial? I can > submit this in coming days on top of current submission. > > > > The current submission status is: > > - Controller operates in CAN FD mode only. > > - If needed to interoperate with CAN 2.0 nodes, data bitrate still need > to be configured and it will work perfectly. However, it is not a "pure" > CAN 2.0 node as mentioned above. > > When you have a CAN FD /capable/ controller the idea is: > > "ip link set can0 up type can bitrate 1000000" > > The controller is in CAN2.0 mode: > > 1. It can send and receive CAN2.0 frames @1MBit/s. > 2. The MTU is set to 16 (sizeof(struct can_frame)) ; CAN_CTRLMODE_FD is > unset. > 3. The CAN controller is not CAN FD tolerant (will produce error frames) > > "ip link set can0 up type can bitrate 1000000 dbitrate 1000000 fd on" > > 1. It can send and receive CAN2.0 frames @1MBit/s. > 2. It can send and receive CAN FD frames @1MBit/s (arbitration&data > bitrate). > 3. The MTU is set to 72 (sizeof(struct canfd_frame)) ; CAN_CTRLMODE_FD is > set. > > For CAN FD frames the data bitrate can be increased like: > "ip link set can0 up type can bitrate 1000000 dbitrate 4000000 fd on" > > So when CAN_CTRLMODE_FD is unset the controller should act like a "pure > CAN2.0" node. Yes & I am glad you clarified this expectation. I think we both agree on this. With my current submission status, the controller can act as a CAN FD node only. Do you agree that the check I had in ndo_open makes sense now? Thanks, Ramesh ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f