Re: [PATCH v5 01/16] drm/prime: Simplify life of drivers needing custom dma_buf_ops

["Christian König" <christian.koenig@amd.com>]

On 10/30/25 15:05, Boris Brezillon wrote:
> drm_gem_is_prime_exported_dma_buf() checks the dma_buf->ops against
> drm_gem_prime_dmabuf_ops, which makes it impossible to use if the
> driver implements custom dma_buf_ops. Instead of duplicating a bunch
> of helpers to work around it, let's provide a way for drivers to
> expose their custom dma_buf_ops so the core prime helpers can rely on
> that instead of hardcoding &drm_gem_prime_dmabuf_ops.

That's generally nice to have, I've re-implemented quite a number of functions in amdgpu because of this as well.

> 
> v5:
> - New patch
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> ---
>  drivers/gpu/drm/drm_prime.c | 14 +++++++++++---
>  include/drm/drm_drv.h       |  8 ++++++++
>  2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 43a10b4af43a..3796844af418 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -903,6 +903,15 @@ unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt)
>  }
>  EXPORT_SYMBOL(drm_prime_get_contiguous_size);
>  
> +static const struct dma_buf_ops *
> +drm_gem_prime_get_dma_buf_ops(struct drm_device *dev)
> +{
> +	if (dev->driver->gem_prime_get_dma_buf_ops)
> +		return dev->driver->gem_prime_get_dma_buf_ops(dev);

I have strong doubts that a driver changes their dma_buf ops during their runtime, so instead of a callback could we just have it as pointer in drm_driver?

Regards,
Christian.

> +
> +	return &drm_gem_prime_dmabuf_ops;
> +}
> +
>  /**
>   * drm_gem_prime_export - helper library implementation of the export callback
>   * @obj: GEM object to export
> @@ -919,7 +928,7 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
>  	struct dma_buf_export_info exp_info = {
>  		.exp_name = KBUILD_MODNAME, /* white lie for debug */
>  		.owner = dev->driver->fops->owner,
> -		.ops = &drm_gem_prime_dmabuf_ops,
> +		.ops = drm_gem_prime_get_dma_buf_ops(dev),
>  		.size = obj->size,
>  		.flags = flags,
>  		.priv = obj,
> @@ -930,7 +939,6 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
>  }
>  EXPORT_SYMBOL(drm_gem_prime_export);
>  
> -
>  /**
>   * drm_gem_is_prime_exported_dma_buf -
>   * checks if the DMA-BUF was exported from a GEM object belonging to @dev.
> @@ -946,7 +954,7 @@ bool drm_gem_is_prime_exported_dma_buf(struct drm_device *dev,
>  {
>  	struct drm_gem_object *obj = dma_buf->priv;
>  
> -	return (dma_buf->ops == &drm_gem_prime_dmabuf_ops) && (obj->dev == dev);
> +	return (dma_buf->ops == drm_gem_prime_get_dma_buf_ops(dev)) && (obj->dev == dev);
>  }
>  EXPORT_SYMBOL(drm_gem_is_prime_exported_dma_buf);
>  
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 42fc085f986d..f18da3c0edb8 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -326,6 +326,14 @@ struct drm_driver {
>  				struct dma_buf_attachment *attach,
>  				struct sg_table *sgt);
>  
> +	/**
> +	 * @gem_prime_get_dma_buf_ops:
> +	 *
> +	 * Optional hook used by the PRIME helpers to get the custom dma_buf_ops
> +	 * used by this driver.
> +	 */
> +	const struct dma_buf_ops *(*gem_prime_get_dma_buf_ops)(struct drm_device *dev);
> +
>  	/**
>  	 * @dumb_create:
>  	 *