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);
@@ -98,7 +98,8 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
 		dma_addr = phys_to_dma(dev, phys);
 		if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
 		    dma_kmalloc_needs_bounce(dev, size, dir)) {
-			if (is_swiotlb_active(dev))
+			if (is_swiotlb_active(dev) &&
+			    !(attrs & DMA_ATTR_REQUIRE_COHERENT))
 				return swiotlb_map(dev, phys, size, dir, attrs);
 
 			goto err_overflow;
@@ -123,7 +124,7 @@ static inline void dma_direct_unmap_phys(struct device *dev, dma_addr_t addr,
 {
 	phys_addr_t phys;
 
-	if (attrs & DMA_ATTR_MMIO)
+	if (attrs & (DMA_ATTR_MMIO | DMA_ATTR_REQUIRE_COHERENT))
 		/* nothing to do: uncached and no swiotlb */
 		return;
 

-- 
2.53.0

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

On Thu, Mar 12, 2026 at 09:20:58AM -0300, Jason Gunthorpe wrote:
> 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() ?

It is better do not call function which is not going to work. We have
same flow for DMA_ATTR_REQUIRE_COHERENT and DMA_ATTR_MMIO, which both
don't work with SWIOTLB.

Thanks

> 
> Jason
>