On Tue, Aug 20, 2019 at 04:58:09PM +0200, Nicolas Saenz Julienne wrote:

Some architectures have platform specific DMA addressing limitations.
This will allow for hardware description code to provide the constraints
in a generic manner, so as for arch code to properly setup it's memory
zones and DMA mask.

I know this just spreads the arm code, but I still kinda hate it.

MAX_DMA_ADDRESS is such an oddly defined concepts.  We have the mm
code that uses it to start allocating after the dma zones, but
I think that would better be done using a function returning
1 << max(zone_dma_bits, 32) or so.  Then we have about a handful
of drivers using it that all seem rather bogus, and one of which
I think are usable on arm64.