On Sun, 24 Oct 2021 23:37:59 +0200, Marc Kleine-Budde wrote: > Hello, > > I'm currently working on runtime configurable RX/TX ring sizes for a the > mcp251xfd CAN driver. > > Unlike modern Ethernet cards with DMA support, most CAN IP cores come > with a fixed size on chip RAM that's used to store received CAN frames > and frames that should be sent. > > For CAN-2.0 only devices that can be directly supported via ethtools's > set/get_ringparam. A minor unaesthetic is, as the on chip RAM is usually > shared between RX and TX, the maximum values for RX and TX cannot be set > at the same time. > > The mcp251xfd chip I'm enhancing supports CAN-2.0 and CAN-FD mode. The > relevant difference of these modes is the size of the CAN frame. 8 vs 64 > bytes of payload + 12 bytes of header. This means we have different > maximum values for both RX and TX for those modes. > > How do we want to deal with the configuration of the two different > modes? As the current set/get_ringparam interface can configure the > mini- and jumbo frames for RX, but has only a single TX value. > > Hao Chen and Guangbin Huang are laying the groundwork to extend the > ringparam interface via netlink: > > | https://lore.kernel.org/all/20211014113943.16231-1-huangguangbin2@xxxxxxxxxx > > I was thinking about adding rx/tx_pending for CAN-FD. The use case would > be to configure the ring parameters independent of the current active > CAN mode. For example in systemd the RX/TX ring parameters are > configured in the .link file, while the CAN FD mode is configured in a > .network file. When switching to the other CAN mode, the previously > configured ring configuration of that CAN mode will be applied to the > hardware. > > In my proof of concept implementation I'm misusing the struct > ethtool_ringparam's mini and jumbo values to pre-configure the CAN-2.0 > and CAN-FD mode's RX ring size, but this is not mainlinable from my > point of view. > > I'm interested in your opinion and use cases. Isn't the simplest setup to stick to the current CAN mode (2.0 vs. FD). Certain values/combinations may be valid in 2.0 and not in FD. So what? This is true also for data-bittiming and what not. I see no advantage in putting your configuration in different files (.link and .network), since they influence each other. I can imaging one network operating in FD, with certain rx/tx settings, and another network operating in 2.0, with different rx/tx settings. and a 3rd network operating in FD, with also different rx/tx settings. If that is a problem for systemd, then ... fix systemd? (systemd is really out of my scope, I'm not used to it) IMHO, you try to provide different default settings (rx/tx split) for FD and 2.0 mode. > > 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 |
