Subject: Re: [PATCH 1/3] drm: Add and export function drm_gem_cma_create_noalloc

From: Daniel Vetter <[email-masked]>
Date: Thu, 1 Oct 2020 10:51:44 +0200

On Wed, Sep 30, 2020 at 07:16:42PM +0200, Paul Cercueil wrote:
> Add and export the function drm_gem_cma_create_noalloc(), which is just
> __drm_gem_cma_create() renamed.
> 
> This function can be used by drivers that need to create a GEM object
> without allocating the backing memory.
> 
> Signed-off-by: Paul Cercueil <[email-masked]>
> ---
>  drivers/gpu/drm/drm_gem_cma_helper.c | 11 ++++++-----
>  include/drm/drm_gem_cma_helper.h     |  3 +++
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 59b9ca207b42..6abc4b306832 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -34,7 +34,7 @@
>   */
>  
>  /**
> - * __drm_gem_cma_create - Create a GEM CMA object without allocating memory
> + * drm_gem_cma_create_noalloc - Create a GEM CMA object without allocating memory
>   * @drm: DRM device
>   * @size: size of the object to allocate
>   *
> @@ -45,8 +45,8 @@
>   * A struct drm_gem_cma_object * on success or an ERR_PTR()-encoded negative
>   * error code on failure.
>   */
> -static struct drm_gem_cma_object *
> -__drm_gem_cma_create(struct drm_device *drm, size_t size)
> +struct drm_gem_cma_object *
> +drm_gem_cma_create_noalloc(struct drm_device *drm, size_t size)
>  {
>  	struct drm_gem_cma_object *cma_obj;
>  	struct drm_gem_object *gem_obj;
> @@ -76,6 +76,7 @@ __drm_gem_cma_create(struct drm_device *drm, size_t size)
>  	kfree(cma_obj);
>  	return ERR_PTR(ret);
>  }
> +EXPORT_SYMBOL_GPL(drm_gem_cma_create_noalloc);

This feels a bit awkward, since for drivers who want to roll their own we
can do that already.

I think the better approach is to export a cma function which allocates
non-coherent dma memory.
-Daniel

>  
>  /**
>   * drm_gem_cma_create - allocate an object with the given size
> @@ -98,7 +99,7 @@ struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
>  
>  	size = round_up(size, PAGE_SIZE);
>  
> -	cma_obj = __drm_gem_cma_create(drm, size);
> +	cma_obj = drm_gem_cma_create_noalloc(drm, size);
>  	if (IS_ERR(cma_obj))
>  		return cma_obj;
>  
> @@ -476,7 +477,7 @@ drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
>  		return ERR_PTR(-EINVAL);
>  
>  	/* Create a CMA GEM buffer. */
> -	cma_obj = __drm_gem_cma_create(dev, attach->dmabuf->size);
> +	cma_obj = drm_gem_cma_create_noalloc(dev, attach->dmabuf->size);
>  	if (IS_ERR(cma_obj))
>  		return ERR_CAST(cma_obj);
>  
> diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
> index 2bfa2502607a..be2b8e3a8ab2 100644
> --- a/include/drm/drm_gem_cma_helper.h
> +++ b/include/drm/drm_gem_cma_helper.h
> @@ -83,6 +83,9 @@ int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma);
>  struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
>  					      size_t size);
>  
> +struct drm_gem_cma_object *
> +drm_gem_cma_create_noalloc(struct drm_device *drm, size_t size);
> +
>  extern const struct vm_operations_struct drm_gem_cma_vm_ops;
>  
>  #ifndef CONFIG_MMU
> -- 
> 2.28.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch