I am on the hunt for the same thing. There has to be a way to kick this up. I ran into this the other day it may be of help.
http://hertaville.com/2013/07/24/interfacing-an-spi-adc-mcp3008-chip-to-the-raspberry-pi-using-c/
lower on the page he says this:
- Write your own custom/optimized ADC device driver. Have a look at the24th (June 2014) edition of the MagPi Magazine. The first article explains how to write a Linux driver for a 6-bit 10MSPS ADC and use it in conjunction with GNUplot to plot the waveforms.
In the magazine article shows things in more detail. He even turns off IRQ's before and then back on after the read.
I have not gotten that far yet. I tried the code in the first link and the Edison does not output the 3 bytes but only one. Yet the same code i tried on 3 other linux boards and they did output 3 bytes. Strange.... So until i figure that out i am stuck.