How to add a generic multi-platform check if DMA can reach a page?

[Aguirre, Sergio]

Hi,

Sorry if I'm asking a basic platform question, but please bear with me a little bit.

I want to know what is the proper generic way of checking if, in my current running
platform, a page is reachable by DMA or not.

The reason of my question is, videobuf library for V4L2 devices is assuming all the time
That pages in Highmem region are _never_ reachable by DMA, no matter what the platform is.

I think that assumption is just not generic enough, so, that's why I want to know
If there's a generic multi-platform mechanism of knowing if a page is reachable by DMA.

I'll appreciate very much your answer/opinion.

Regards,
Sergio