Their Sparx-5 line is supported by stock upstream Linux switchdev.

You are right, the situation is better that what I thought, the commercial smbstax SDK might not be absolutely required.

They even have some BSP stuff freely available which is really positive sign. https://github.com/microchip-ung/bsp-doc

This would be such an enticing project to jump into, there are just enough bits to make it seem doable, even if the realist in me knows its not really feasible.

Intrigued by that, I went looking. First commit of support was 2019, for Linux5.2. Yet, 5 years later, there is not one example (that i could find) of OpenWrt running on these Chips. If the platform/FW/BSP package were any good, I'd expect there to be chat about it in the forums, and/or attempts to port to such devices from SMBStaX (The Microchip BSP Linux dist).

I suspect it's not worth the effort for most people. People who want to DIY a switch are likely content to brute force it with a decent cpu, multiport network cards, and lots of PCIe lanes. While others will be happy with a used enterprise OEM unit.

Does make me wonder what asics Microtik is using under the hood though...

A lot of them are just networking SoCs with built in switching fabrics or the lower end ones have the low end router SoC from various manufacturers.

Mikrotik is one of the few brands that actually list this in the spec sheets.

That's a very cheap price for enterprise layer 3 switching chip. Thanks for the info, how this switch chip has escaped me is very perplexing.

Can you elaborate on their Linux-based package, is the package critical for the development and using the chip with embedded Linux. Can we just use it as switching fabric and use Intel CPU for example N100 as the main controller running Linux?

The sibling comment also mentioned that Sparx-5 line is supported by stock upstream Linux switchdev, and this the same chip as in your link.