Re: [PATCH 2/7] drm/gpusvm: use more selective dma dir in get_pages()

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Thu, 2025-03-20 at 17:29 +0000, Matthew Auld wrote:
> If we are only reading the memory then from the device pov the
> direction
> can be DMA_TO_DEVICE. This aligns with the xe-userptr code. Using the
> most restrictive data direction to represent the access is normally a
> good idea.
> 
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

> ---
>  drivers/gpu/drm/drm_gpusvm.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c
> b/drivers/gpu/drm/drm_gpusvm.c
> index 48993cef4a74..7f1cf5492bba 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -1355,6 +1355,8 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
>  	int err = 0;
>  	struct dev_pagemap *pagemap;
>  	struct drm_pagemap *dpagemap;
> +	enum dma_data_direction dma_dir = ctx->read_only ?
> DMA_TO_DEVICE :
> +							  
> DMA_BIDIRECTIONAL;
>  
>  retry:
>  	hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
> @@ -1459,7 +1461,7 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
>  				dpagemap->ops->device_map(dpagemap,
>  							  gpusvm-
> >drm->dev,
>  							  page,
> order,
> -							 
> DMA_BIDIRECTIONAL);
> +							  dma_dir);
>  			if (dma_mapping_error(gpusvm->drm->dev,
>  					      range-
> >dma_addr[j].addr)) {
>  				err = -EFAULT;
> @@ -1478,7 +1480,7 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
>  			addr = dma_map_page(gpusvm->drm->dev,
>  					    page, 0,
>  					    PAGE_SIZE << order,
> -					    DMA_BIDIRECTIONAL);
> +					    dma_dir);
>  			if (dma_mapping_error(gpusvm->drm->dev,
> addr)) {
>  				err = -EFAULT;
>  				goto err_unmap;
> @@ -1486,7 +1488,7 @@ int drm_gpusvm_range_get_pages(struct
> drm_gpusvm *gpusvm,
>  
>  			range->dma_addr[j] =
> drm_pagemap_device_addr_encode
>  				(addr, DRM_INTERCONNECT_SYSTEM,
> order,
> -				 DMA_BIDIRECTIONAL);
> +				 dma_dir);
>  		}
>  		i += 1 << order;
>  		num_dma_mapped = i;