Re: [PATCH v3 1/4] drm: rework description of primary and cursor planes

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Fri, 11 Dec 2020 13:06:10 +0000
Simon Ser <contact@emersion.fr> wrote:

> The previous wording could be understood by user-space evelopers as "a
> primary/cursor plane is only compatible with a single CRTC" [1].
> 
> Reword the planes description to make it clear the DRM-internal
> drm_crtc.primary and drm_crtc.cursor planes are for legacy uAPI.
> 
> [1]: https://github.com/swaywm/wlroots/pull/2333#discussion_r456788057
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>

Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>


> ---
>  drivers/gpu/drm/drm_crtc.c  |  3 +++
>  drivers/gpu/drm/drm_plane.c | 16 +++++++++-------
>  2 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index 8d19d258547f..a6336c7154d6 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -256,6 +256,9 @@ struct dma_fence *drm_crtc_create_fence(struct drm_crtc *crtc)
>   * planes). For really simple hardware which has only 1 plane look at
>   * drm_simple_display_pipe_init() instead.
>   *
> + * The @primary and @cursor planes are only relevant for legacy uAPI, see
> + * &drm_crtc.primary and &drm_crtc.cursor.
> + *
>   * Returns:
>   * Zero on success, error code on failure.
>   */
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 385801dd21f9..5d33ca9f0032 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -49,14 +49,16 @@
>   * &struct drm_plane (possibly as part of a larger structure) and registers it
>   * with a call to drm_universal_plane_init().
>   *
> - * Cursor and overlay planes are optional. All drivers should provide one
> - * primary plane per CRTC to avoid surprising userspace too much. See enum
> - * drm_plane_type for a more in-depth discussion of these special uapi-relevant
> - * plane types. Special planes are associated with their CRTC by calling
> - * drm_crtc_init_with_planes().
> - *
>   * The type of a plane is exposed in the immutable "type" enumeration property,
> - * which has one of the following values: "Overlay", "Primary", "Cursor".
> + * which has one of the following values: "Overlay", "Primary", "Cursor" (see
> + * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see
> + * &drm_plane.possible_crtcs.
> + *
> + * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
> + * relies on the driver to set the primary and optionally the cursor plane used
> + * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All
> + * drivers should provide one primary plane per CRTC to avoid surprising legacy
> + * userspace too much.
>   */
>  
>  static unsigned int drm_num_planes(struct drm_device *dev)


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