On 29.07.2022 08:52:07, Dario Binacchi wrote: > Hello Marc and Max, > > On Thu, Jul 28, 2022 at 12:57 PM Max Staudt <max@xxxxxxxxx> wrote: > > > > On Thu, 28 Jul 2022 12:50:49 +0200 > > Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> wrote: > > > > > On 28.07.2022 12:23:04, Dario Binacchi wrote: > > > > > > Does it make sense to use the device tree > > > > > > > > > > The driver doesn't support DT and DT only works for static serial > > > > > interfaces. > > > > > > Have you seen my remarks about Device Tree? > > > > Dario, there seems to be a misunderstanding about the Device Tree. > > > > It is used *only* for hardware that is permanently attached, present at > > boot, and forever after. Not for dyamically added stuff, and definitely > > not for ldiscs that have to be attached manually by the user. > > > > > > The only exception to this is if you have an embedded device with an > > slcan adapter permanently attached to one of its UARTs. Then you can > > use the serdev ldisc adapter to attach the ldisc automatically at boot. > > It is evident that I am lacking some skills (I will try to fix it :)). We're all here to learn something! > I think it is equally clear that it is not worth going down this path. If you have a static attached serial devices serdev is the way to go. But slcan has so many drawbacks compared to "real" CAN adapters that I hope the no one uses them in such a scenario. > > If you are actively developing for such a use case, please let us know, > > so we know what you're after and can help you better :) > > I don't have a use case, other than to try, if possible, to make the driver > autonomous from slcand / slcan_attach for the CAN bus setup. From my point of view your job is done! > Returning to Marc's previous analysis: > "... Some USB CAN drivers query the bit timing const from the USB device." > > Can we think of taking the gs_usb driver as inspiration for getting/setting the > bit timings? > > https://elixir.bootlin.com/linux/latest/source/drivers/net/can/usb/gs_usb.c#L951 > https://elixir.bootlin.com/linux/latest/source/drivers/net/can/usb/gs_usb.c#L510 > > and, as done with patches: > > can: slcan: extend the protocol with CAN state info > can: slcan: extend the protocol with error info You can define a way to query bit timing constants and CAN clock rate, but you have to get this into the "official" firmware. You have to roll out a firmware update to all devices. What about non official firmware? > further extend the protocol to get/set the bit timing from / to the adapter ? > In the case of non-standard bit rates, the driver would try, depending on the > firmware of the adapter, to calculate and set the bit timings autonomously. If an adapter follows 100% the official firmware doc the BTR registers are interpreted as SJA1000 with 8 MHz CAN clock. See | https://lore.kernel.org/all/20220728105049.43gbjuctezxzmm4j@xxxxxxxxxxxxxx where I compare the 125 Kbit/s BTR config of the documentation with the bit timing calculated by the kernel algorithm. regards, 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 |
Attachment:
signature.asc
Description: PGP signature
