Re: [PATCH] swiotlb: Fix inversed DMA_ATTR_NO_WARN test

[Christoph Hellwig]

On Wed, May 02, 2018 at 02:18:56PM +0200, Daniel Vetter wrote:
> Other dma-api backends like cma just shut up when __GFP_NOWARN is
> passed. And afaiui Christoph Hellwig has plans to nuke the DMA_ATTR
> stuff (or at least clean it up) - should we just remove
> DMA_ATTR_NO_WARN and instead only look at __GFP_NOWARN?

No.  __GFP_NOWARN (and gfp_t flags in general) are the wrong interface
for dma allocations and just cause problems.  I actually plan to
get rid of the gfp_t argument in dma_alloc_attrs sooner, and only
allow either GFP_KERNEL or GFP_DMA passed in dma_alloc_coherent.

> Or maybe we should at least enforce that both or none are set, for
> consistency for now?

The interface should be DMA_ATTR_NO_WARN.  __GFP_NOWARN in this
context was never documented, and just slipped in.