Re: [RFC 0/7] Support in-kernel DMA with PASID and SVA

[Jason Gunthorpe]

On Thu, Oct 07, 2021 at 10:50:10AM -0700, Jacob Pan wrote:

> On platforms that are DMA snooped, this barrier is not needed. But I think
> your point is that once we convert to DMA API, the sync/barrier is covered
> by DMA APIs if !dev_is_dma_coherent(dev). Then all archs are good.

No.. my point is that a CPU store release is not necessary a DMA
visiable event on all platforms and things like dma_wmb/rmb() may
still be necessary. This all needs to be architected before anyone
starts writing drivers that assume a coherent DMA model without using
a coherent DMA allocation.

Jason