Re: [PATCH v4 01/14] drm/atomic: export drm_atomic_replace_property_blob

[Daniel Vetter]

On Thu, Jul 06, 2017 at 02:20:35PM +0200, Peter Rosin wrote:
> While at it, add some words in the kernel-doc about the 'replaced' arg and
> remove a faulty kernel-doc comment on the return value.
> 
> Also remove a redundant return statement.
> 
> Signed-off-by: Peter Rosin <peda@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_atomic.c | 17 +++++++++--------
>  include/drm/drm_atomic.h     |  4 ++++
>  2 files changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 09ca662..b7d9696 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -414,13 +414,15 @@ EXPORT_SYMBOL(drm_atomic_set_mode_prop_for_crtc);
>   * @new_blob: the new blob to replace with
>   * @replaced: whether the blob has been replaced
>   *
> - * RETURNS:
> - * Zero on success, error code on failure
> + * Note that you are required to initialize @replaced to false before the
> + * call, since it is only set to true when the blob property is changed and
> + * not set to false when the property is not changed. This enables a series
> + * of calls to be made where you are interested in if any property is
> + * replaced, but not care so much about exactly which of them was replaced.
>   */
> -static void
> -drm_atomic_replace_property_blob(struct drm_property_blob **blob,
> -				 struct drm_property_blob *new_blob,
> -				 bool *replaced)
> +void drm_atomic_replace_property_blob(struct drm_property_blob **blob,
> +				      struct drm_property_blob *new_blob,
> +				      bool *replaced)

Yes I know I'm super-annoying, but this function now feels misplaced. It
has nothing to do with atomic, it just replaces a pointer to a blob with
anther pointer. I think it'd be much better if we move this function to
drm_property.c, and rename it to drm_property_replace_blob.

Second, instead of typing a huge paragraph explaining how replaced works,
I think the better option would be to drop that parameter and instead
return a boolean indicating whether the blob was replaced or not.

That's a bit more work, but imo functions which are exported need to pass
a higher barrier wrt api polish.

Thanks, Daniel

>  {
>  	struct drm_property_blob *old_blob = *blob;
>  
> @@ -432,9 +434,8 @@ drm_atomic_replace_property_blob(struct drm_property_blob **blob,
>  		drm_property_blob_get(new_blob);
>  	*blob = new_blob;
>  	*replaced = true;
> -
> -	return;
>  }
> +EXPORT_SYMBOL(drm_atomic_replace_property_blob);
>  
>  static int
>  drm_atomic_replace_property_blob_from_id(struct drm_device *dev,
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index dcc8e0c..8b32ea5 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -321,6 +321,10 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
>  		struct drm_connector_state *state, struct drm_property *property,
>  		uint64_t val);
>  
> +void drm_atomic_replace_property_blob(struct drm_property_blob **blob,
> +				      struct drm_property_blob *new_blob,
> +				      bool *replaced);
> +
>  void * __must_check
>  drm_atomic_get_private_obj_state(struct drm_atomic_state *state,
>  			      void *obj,
> -- 
> 2.1.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch