Adding decoded Chip Select capability to the kernel SPI driver

["Tim Barr" <tbarr@xxxxxxxxxxxxx>]

I am looking at how to add decoded chip select capability to my
AT91SAM9G20 design at the kernel level. I wanted to throw out an
approach to this to see if it makes sense from the kernel level. 
 
The first item would be a control bit to set up the driver to operate in
either a decoded or straight chip select mode. In the spi_device struct
there is a u8 variable called 'mode' defined. Of the eight bits in the
word, 6 bits are assigned and 2 are undefined. I am not sure if I should
one of these undefined bits as a "encode_CS" bit, or if I should add an
additional variable to the end of the struct.
 
Since the Atmel SPI driver controls the CS pins as GPIOs, instead of
using the SPI engine, I assume that it will not be too difficult to
modify the code to allow either straight or encoded chip select
operation. Looking at the code, I am thinking of adding the CS encoding
code to the cs_activate and cs_deactivate processes. Does that make
sense? 
 
Thanks!


Timothy Barr
Hardware Development Engineer
for Multi-Tech Systems, Inc.
 <mailto:tbarr@xxxxxxxxxxxxx> tbarr@xxxxxxxxxxxxx 

 
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