How to use SPI

[Gergely Czuczy]

Hello,

I've just got a Raspberry PI3, and I would like to use a couple of 
Adaruit MAX31856 breakout boards with it, which are using the SPI bus. 
I've noticed that it apparently has kernel level spi drivers:

# kldstat -v | grep spi
                 259 simplebus/bcm2835_spi
                 109 spi/spibus
                 108 spi/ofw_spibus

However, I wasn't able to find anything in the userland which would 
explain how to use it.

Currently I'm using a raspbsd image:

FreeBSD rpi3 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r313109M: Thu Feb  2 
16:16:39 MST 2017 
raspberry at hive.raspbsd.org:/usr/home/brd/rpi3/crochet/work/obj/arm64.aarch64/usr/src/sys/GENERIC 
arm64

Could you guys please give me a hand on starting using the SPI bus? I've 
tried googling around a bit, but unfortunately not much came up.

Best regards,
Gergely