Re: [PATCH v2 7/7] pmem, dax: have direct_access use __pmem annotation

From: Dan Williams
Date: Sat Aug 15 2015 - 14:05:36 EST

On Sat, Aug 15, 2015 at 9:00 AM, Christoph Hellwig <hch@xxxxxx> wrote:
> On Sat, Aug 15, 2015 at 08:44:27AM -0700, Dan Williams wrote:
>> That said, while we don't need special accessors we do need guarantees
>> that anything that has written to a persistent memory address has done
>> so in a way that wmb_pmem() is able to flush it. It's more of a "I've
>> audited this code path for wmb_pmem() compatibility so use this api to
>> write to pmem."
> I'm more worried about things where don't just do plain loads and stores
> to a pmem region but DMA, which will end up as a nightmare of casts.
> But we can wait and see how that evolves in the end..

It's already not possible to do something like dma_map_single() on an
ioremap()'d address, so there currently are't any __iomem/DMA
collisions. As long as DMA setup is relative to a physical address
resource I think we're ok.

Making sure a DMA is both complete and persistent though is a different problem.
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