On Wed, Jan 10, 2018 at 12:58:14PM +0000, Robin Murphy wrote:

On 10/01/18 08:09, Christoph Hellwig wrote:

quoted

arm64 uses ZONE_DMA for allocations below 32-bits.  These days we
name the zone for that ZONE_DMA32, which will allow to use the
dma-direct and generic swiotlb code as-is, so rename it.

I do wonder if we could also "upgrade" GFP_DMA to GFP_DMA32 somehow when 
!ZONE_DMA - there are almost certainly arm64 drivers out there using a 
combination of GFP_DMA and streaming mappings which will no longer get the 
guaranteed 32-bit addresses they expect after this. I'm not sure quite how 
feasible that is, though :/

I can't find anything obvious in the tree. The alternative would be
to keep ZONE_DMA and set ARCH_ZONE_DMA_BITS.

That said, I do agree that this is an appropriate change (the legacy of 
GFP_DMA is obviously horrible), so, provided we get plenty of time to find 
and fix the fallout when it lands:

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

I was hoping to get this into 4.15.  What would be proper time to
fix the fallout?