How many SPI ports/buses are broken out/available on SOQUARTZ?

[CounterPillow]

I looked at the schematic and datasheet to figure out whether there's any way to access SPI1/SPI2 with a different pinmux, and it doesn't seem to be the case. Seems like this module sadly won't work for your use-case.

You've almost addressed my next question. 

I'm now re-evaluating my own options to see if I can change my application code to use the same SPI bus but flip between slave devices using different CS (chip select) - it's messy, a little complex with timings, but possible.

As such, it is not clear to me how to define my two CS's inside the device tree overlay. 

Are the pin control pinmux references preset for each CS or do I still need to add inside the device tree overlay for my spi driver? If so, where do I find this pinmux table?

I also note that there are various device tree overlay templates found on the radxa github repository page (https://github.com/radxa/overlays/) which are applicable for use with RK386x chipsets and are defined as compatible with "rockchip". I assume these are suitable for use with the Pine64 SOQuartz board.

So assuming that's the case, and as SPI3 is available on the SOQuartz, am I correct to then create an overlay fragment for <&spi3> and then use the same pinctrl-0 pin references for CS0: <&spi3m0_cs0 &spi3m0_pins>;

Then what about CS1, as I noticed that Radxa's own compute module (RK3566 CM3) uses a different pin number here. Do I then assume that you have correctly linked the reference  &spi3m0_cs1 to the correct pin in the RK3566. As I don't have visibility on how this all works, it is hard to know.

I look forward to your feedback.

Thanks.

The pinctrl for the m0 pinmux is already in the base device tree of rk356x.dtsi, no overlay is needed to change the pinmuxes in this case. When you're writing a device tree overlay to enable SPI, you can simply leave out the pinctrl properties; the ones from the base tree will be used.

If you had to change some pinmuxes, you'd do it by copying the definitions of the pins from rk3568-pinctrl.dtsi to your overlay first, as they get omitted from the base tree if there's no reference. I plan on writing some example overlays myself for SPI stuff on soquartz over at https://github.com/CounterPillow/overlay-examples soon, I just haven't gotten around to it yet.

In general, I would not try to use radxa's overlays; I'm pretty sure they target their own probably downstream based kernels.