Return BUS_PROBE_NOWILDCARD in probe method to make sure that spigen
attaches only to the device created in identify method.
Before this change spigen probe method used to return 0 which meant it
competed with other drivers to be attached to the devices created for
child nodes of SPI bus node in FDT.
Reported by: Daniel Braniss
MFC after: 1 week
Make st_data part of spigen_transfer optional by letting pass zero length
and NULL pointer. SPI controller drivers handle this case fine.
MFC after: 1 week
This is a simple ioctl and mmap API to issue SPI transactions from
userland. It's useful for simple devices (eg spi temperature sensors,
etc) for experimentation.
TODO:
* Write some documentation!
Submitted by: green
