I have been working on applications using the SPI user space api. One of the devices I have been playing with is a PN523 NFC reader. The reader is supported by libnfc and can communicate using serial, SPI, i2c or usb depending on device support.
I wanted to get the nfc reader working over i2c, to form a baseline to compare it against SPI. I couldn't get the nfc-list to show any NFC devices connected to the Pi. I then tried to use the i2c -s command to scan the i2c bus, but instead of device detection the command threw an error.
It turns out that the iic driver for the Pi only supports one ioctl, I2CRDWR. That neuters most of the FreeBSD i2c tools as they use other ioctl's and error out on failure.
Learning that I looked at the Makefile for libnfc, this time realising that the i2c and the SPI device options are both commented out. I missed this the first time I looked at the FreeBSD port, there is still the option to use a serial device once I dig out a usb serial adapter.
It is looking a lot harder than I thought to get devices working with user space SPI on FreeBSD. It doesn't help that Linux has been the only operating system with user space SPI support for quite a long time.