Re: [PATCH v2 5/8] dma-direct: prevent SWIOTLB path when DMA_ATTR_REQUIRE_COHERENT is set

Jason Gunthorpe
2026-03-12T12:21:04Z

On Wed, Mar 11, 2026 at 09:08:48PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
>
> DMA_ATTR_REQUIRE_COHERENT indicates that SWIOTLB must not be used.
> Ensure the SWIOTLB path is declined whenever the DMA direct path is
> selected.
>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
> kernel/dma/direct.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
> index e89f175e9c2d0..6184ff303f080 100644
> --- a/kernel/dma/direct.h
> +++ b/kernel/dma/direct.h
> @@ -84,7 +84,7 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
> dma_addr_t dma_addr;
>
> if (is_swiotlb_force_bounce(dev)) {
> - if (attrs & DMA_ATTR_MMIO)
> + if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
> return DMA_MAPPING_ERROR;
>
> return swiotlb_map(dev, phys, size, dir, attrs);

Oh here it is, still maybe it is better to put it in swiotlb_map() ?

Jason