Name
spi_w8r8 — 
     SPI synchronous 8 bit write followed by 8 bit read
 
Arguments
- spi
- 
     device with which data will be exchanged
     
- cmd
- 
     command to be written before data is read back
     
Description
   Callable only from contexts that can sleep.
Return
   the (unsigned) eight bit number returned by the
   device, or else a negative error code.