Linux spi driver

I am looking for help with writing a spi linux driver with two slaves via a device tree structure

I have a device tree with a controller node and 3 slave nodes

I will like to have a spi driver that can communicate with the tree slaves passing through the controller

The following questions in particular
1) How to attach the 3 slaves to the controller
2) How to specify message to each slave individually from userspace i.e. how is the chip_select for each slave specified during the communication