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. 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 |
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