Extended functionality for SPI core

["Hegbeli, Ciprian" <Ciprian.Hegbeli@xxxxxxxxxx>]

Hi,

I am currently extending the functionality of a SPI driver for a HDL based IP core.
The new features will include QSPI functionality and DDR capabilities, for an ADC.
My question is regarding the DDR functionality; the ADC expects only the data to 
be transmitted using both edges while the register address will be on a single rate
transmission. As I am extending the feature set of the SPI core I would like to maintain 
backwards compatibility to what we already have implemented using the linux-spi
framework.

I think that the easiest way to achieve this would be to somehow pass the information
using the spi_transfer structure, using a flag in which I would specify if the particular 
transfer is DDR or not. The structure however does not support this functionality.

As this is probably not the only feature that the IP core will probably have in future 
development, I'm curious if there is a way of passing new flags/variables/structure 
attributes using the current SPI framework? Or what would be the correct way to
include the extended functionality of the SPI core if there are no mechanisms for
it in the current linux-spi framework?

Regards,
Ciprian Hegbeli