passing function pointers through platform devices?

[NZG <ngustavson@emacinc.com>]

I'm developing an SPI- bus >MMC/SD block driver translation layer.
As part of this layer the write protect and card detect lines need to be read.
The method for determining the state of these lines will be board specific.

Is it appropriate to pass a function pointer through a platform device 
(declared in the mach initialization) to implement card_available and 
write_protect function calls?
Or is there a cleaner way to do it?

thank you,
NZG