Re: [PATCH v7 2/8] drm/ttm: Add ttm_bo_access

[Christian König <christian.koenig@xxxxxxx>]

Am 26.11.24 um 18:46 schrieb Matthew Brost:
> Non-contiguous VRAM cannot easily be mapped in TTM nor can non-visible
> VRAM easily be accessed. Add ttm_bo_access, which is similar to
> ttm_bo_vm_access, to access such memory.
>
> v4:
>   - Fix checkpatch warnings (CI)
> v5:
>   - Fix checkpatch warnings (CI)
> v6:
>   - Fix kernel doc (Auld)
> v7:
>   - Move ttm_bo_access to ttm_bo_vm.c (Christian)
>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Reported-by: Christoph Manszewski <christoph.manszewski@xxxxxxxxx>
> Suggested-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> Tested-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

> ---
>   drivers/gpu/drm/ttm/ttm_bo_vm.c | 40 ++++++++++++++++++++++++++-------
>   include/drm/ttm/ttm_bo.h        |  2 ++
>   2 files changed, 34 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 2c699ed1963a..f02d3966cc84 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -405,13 +405,25 @@ static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo,
>   	return len;
>   }
>   
> -int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
> -		     void *buf, int len, int write)
> +/**
> + * ttm_bo_access - Helper to access a buffer object
> + *
> + * @bo: ttm buffer object
> + * @offset: access offset into buffer object
> + * @buf: pointer to caller memory to read into or write from
> + * @len: length of access
> + * @write: write access
> + *
> + * Utility function to access a buffer object. Useful when buffer object cannot
> + * be easily mapped (non-contiguous, non-visible, etc...). Should not directly
> + * be exported to user space via a peak / poke interface.
> + *
> + * Returns:
> + * @len if successful, negative error code on failure.
> + */
> +int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset,
> +		  void *buf, int len, int write)
>   {
> -	struct ttm_buffer_object *bo = vma->vm_private_data;
> -	unsigned long offset = (addr) - vma->vm_start +
> -		((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
> -		 << PAGE_SHIFT);
>   	int ret;
>   
>   	if (len < 1 || (offset + len) > bo->base.size)
> @@ -429,8 +441,8 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
>   		break;
>   	default:
>   		if (bo->bdev->funcs->access_memory)
> -			ret = bo->bdev->funcs->access_memory(
> -				bo, offset, buf, len, write);
> +			ret = bo->bdev->funcs->access_memory
> +				(bo, offset, buf, len, write);
>   		else
>   			ret = -EIO;
>   	}
> @@ -439,6 +451,18 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
>   
>   	return ret;
>   }
> +EXPORT_SYMBOL(ttm_bo_access);
> +
> +int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
> +		     void *buf, int len, int write)
> +{
> +	struct ttm_buffer_object *bo = vma->vm_private_data;
> +	unsigned long offset = (addr) - vma->vm_start +
> +		((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
> +		 << PAGE_SHIFT);
> +
> +	return ttm_bo_access(bo, offset, buf, len, write);
> +}
>   EXPORT_SYMBOL(ttm_bo_vm_access);
>   
>   static const struct vm_operations_struct ttm_bo_vm_ops = {
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index 5804408815be..8ea11cd8df39 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -421,6 +421,8 @@ void ttm_bo_unpin(struct ttm_buffer_object *bo);
>   int ttm_bo_evict_first(struct ttm_device *bdev,
>   		       struct ttm_resource_manager *man,
>   		       struct ttm_operation_ctx *ctx);
> +int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset,
> +		  void *buf, int len, int write);
>   vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
>   			     struct vm_fault *vmf);
>   vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,