Re: [PATCH 21/22] arm64: replace ZONE_DMA with ZONE_DMA32

Robin Murphy
2018-01-10T17:10:09Z

On 10/01/18 15:55, Christoph Hellwig wrote:
> On Wed, Jan 10, 2018 at 04:55:17PM +0100, Christoph Hellwig wrote:
>> On Wed, Jan 10, 2018 at 12:58:14PM +0000, Robin Murphy wrote:
>>> On 10/01/18 08:09, Christoph Hellwig wrote:
>>>> 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?
>
> Err, 4.16 of course.

Hee hee - cramming it into 4.15 is exactly what I wouldn't want to do,
even if Linus would accept it :)

Landing it this merge window for 4.16-rc1 sounds good if we can manage that.

Robin.