An example SPI driver using some Microchip MCP3002 ADC's as the slave devices
connected to a Gumstix Overo off the SPI1 header pins.  I have two of the ADCs
hooked up to CS0 and CS1. 

This driver probably works with Beagleboards too, with some changes for the
exposed SPI module. I haven't checked yet.

The Makefile assumes you are using the included overo-source-me.txt and have a
working OE cross-build environment set up.

You should not have the ADS7846 touchscreen driver enabled in your kernel
either as a module or built-in or you won't be able to load this device.
Can't have two devices asking for the same CS0 line.

There are some required kernel patches in order to handle the dynamic 
adding of spi devices. I submitted them to the linux-omap list, but it 
may be awhile before they show up in the gumstix kernel.  

I provided the patches in this project until then.

Update: The patches were accepted into 2.6.34 mainline

Assuming your running 2.6.32, copy the patches 1 and 2 to 

../recipes/linux/linux-omap3-2.6.32/

and then patch your 

../recipes/linux/linux-omap3_2.6.32.bb 

to look like the one in this project or just use this one.

The interface is a character device. The /dev/adc node will be created
when you load the module.

The write commands are on and off
root@overo# echo on > /dev/adc
root@overo# echo off > /dev/adc

The read command returns either
root@overo# cat /dev/adc
ADC: off
or 
root@overo# cat /dev/adc
ADC: <adc_1_val> <adc_2_val>

The omap2_mcspi module needs to be loaded before adc.ko

The driver is for playing around with Linux OMAP3 SPI stuff. It's not 
for production. There are printk's galore and they are all ALERTS of 
course.

Enjoy.