Re: [PATCH RFC v4 2/7] drm: Introduce pixel_source DRM plane property

[Sebastian Wick <sebastian.wick@redhat.com>]

On Fri, Jun 30, 2023 at 2:26 AM Jessica Zhang <quic_jesszhan@quicinc.com> wrote:
>
> Add support for pixel_source property to drm_plane and related
> documentation.
>
> This enum property will allow user to specify a pixel source for the
> plane. Possible pixel sources will be defined in the
> drm_plane_pixel_source enum.
>
> The current possible pixel sources are DRM_PLANE_PIXEL_SOURCE_FB and
> DRM_PLANE_PIXEL_SOURCE_COLOR. The default value is *_SOURCE_FB.
>
> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
> ---
>  drivers/gpu/drm/drm_atomic_state_helper.c |  1 +
>  drivers/gpu/drm/drm_atomic_uapi.c         |  4 ++
>  drivers/gpu/drm/drm_blend.c               | 81 +++++++++++++++++++++++++++++++
>  include/drm/drm_blend.h                   |  2 +
>  include/drm/drm_plane.h                   | 21 ++++++++
>  5 files changed, 109 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic_state_helper.c b/drivers/gpu/drm/drm_atomic_state_helper.c
> index fe14be2bd2b2..86fb876efbe6 100644
> --- a/drivers/gpu/drm/drm_atomic_state_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_state_helper.c
> @@ -252,6 +252,7 @@ void __drm_atomic_helper_plane_state_reset(struct drm_plane_state *plane_state,
>
>         plane_state->alpha = DRM_BLEND_ALPHA_OPAQUE;
>         plane_state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> +       plane_state->pixel_source = DRM_PLANE_PIXEL_SOURCE_FB;
>
>         if (plane_state->solid_fill_blob) {
>                 drm_property_blob_put(plane_state->solid_fill_blob);
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index a28b4ee79444..6e59c21af66b 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -596,6 +596,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>                 drm_property_blob_put(solid_fill);
>
>                 return ret;
> +       } else if (property == plane->pixel_source_property) {
> +               state->pixel_source = val;
>         } else if (property == plane->alpha_property) {
>                 state->alpha = val;
>         } else if (property == plane->blend_mode_property) {
> @@ -671,6 +673,8 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
>         } else if (property == plane->solid_fill_property) {
>                 *val = state->solid_fill_blob ?
>                         state->solid_fill_blob->base.id : 0;
> +       } else if (property == plane->pixel_source_property) {
> +               *val = state->pixel_source;
>         } else if (property == plane->alpha_property) {
>                 *val = state->alpha;
>         } else if (property == plane->blend_mode_property) {
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index 38c3c5d6453a..8c100a957ee2 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -189,6 +189,18 @@
>   *     solid_fill is set up with drm_plane_create_solid_fill_property(). It
>   *     contains pixel data that drivers can use to fill a plane.
>   *
> + * pixel_source:
> + *     pixel_source is set up with drm_plane_create_pixel_source_property().
> + *     It is used to toggle the source of pixel data for the plane.
> + *
> + *     Possible values:
> + *
> + *     "FB":
> + *             Framebuffer source
> + *
> + *     "COLOR":
> + *             solid_fill source
> + *
>   * Note that all the property extensions described here apply either to the
>   * plane or the CRTC (e.g. for the background color, which currently is not
>   * exposed and assumed to be black).
> @@ -648,3 +660,72 @@ int drm_plane_create_solid_fill_property(struct drm_plane *plane)
>         return 0;
>  }
>  EXPORT_SYMBOL(drm_plane_create_solid_fill_property);
> +
> +/**
> + * drm_plane_create_pixel_source_property - create a new pixel source property
> + * @plane: drm plane
> + * @supported_sources: bitmask of supported pixel_sources for the driver (NOT
> + *                     including DRM_PLANE_PIXEL_SOURCE_FB, as it will be supported
> + *                     by default).
> + *
> + * This creates a new property describing the current source of pixel data for the
> + * plane.
> + *
> + * The property is exposed to userspace as an enumeration property called
> + * "pixel_source" and has the following enumeration values:
> + *
> + * "FB":
> + *     Framebuffer pixel source
> + *
> + * "COLOR":
> + *     Solid fill color pixel source

Can we add a "NONE" value?

I know it has been discussed earlier if we *need*  this and I don't
think we do. I just think it would be better API design to disable
planes this way than having to know that a framebuffer pixel source
with a NULL framebuffer disables the plane. Obviously also keep the
old behavior for backwards compatibility.

> + *
> + * Returns:
> + * Zero on success, negative errno on failure.
> + */
> +int drm_plane_create_pixel_source_property(struct drm_plane *plane,
> +                                          unsigned int supported_sources)
> +{
> +       struct drm_device *dev = plane->dev;
> +       struct drm_property *prop;
> +       const struct drm_prop_enum_list enum_list[] = {
> +               { DRM_PLANE_PIXEL_SOURCE_FB, "FB" },
> +               { DRM_PLANE_PIXEL_SOURCE_COLOR, "COLOR" },
> +       };
> +       unsigned int valid_source_mask = BIT(DRM_PLANE_PIXEL_SOURCE_FB) |
> +                                      BIT(DRM_PLANE_PIXEL_SOURCE_COLOR);
> +       int i;
> +
> +       /* FB is supported by default */
> +       supported_sources |= BIT(DRM_PLANE_PIXEL_SOURCE_FB);
> +
> +       if (WARN_ON(supported_sources & ~valid_source_mask))
> +               return -EINVAL;
> +
> +       prop = drm_property_create(dev, DRM_MODE_PROP_ENUM, "pixel_source",
> +                       hweight32(supported_sources));
> +
> +       if (!prop)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < ARRAY_SIZE(enum_list); i++) {
> +               int ret;
> +
> +               if (!(BIT(enum_list[i].type) & supported_sources))
> +                       continue;
> +
> +               ret = drm_property_add_enum(prop, enum_list[i].type, enum_list[i].name);
> +
> +               if (ret) {
> +                       drm_property_destroy(dev, prop);
> +
> +                       return ret;
> +               }
> +       }
> +
> +       drm_object_attach_property(&plane->base, prop, DRM_PLANE_PIXEL_SOURCE_FB);
> +       plane->pixel_source_property = prop;
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(drm_plane_create_pixel_source_property);
> diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
> index 0338a860b9c8..31af7cfa5b1b 100644
> --- a/include/drm/drm_blend.h
> +++ b/include/drm/drm_blend.h
> @@ -59,4 +59,6 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
>  int drm_plane_create_blend_mode_property(struct drm_plane *plane,
>                                          unsigned int supported_modes);
>  int drm_plane_create_solid_fill_property(struct drm_plane *plane);
> +int drm_plane_create_pixel_source_property(struct drm_plane *plane,
> +                                          unsigned int supported_sources);
>  #endif
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index f6ab313cb83e..73fb6cf8a5d9 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -59,6 +59,12 @@ struct drm_solid_fill {
>         uint32_t b;
>  };
>
> +enum drm_plane_pixel_source {
> +       DRM_PLANE_PIXEL_SOURCE_FB,
> +       DRM_PLANE_PIXEL_SOURCE_COLOR,
> +       DRM_PLANE_PIXEL_SOURCE_MAX
> +};
> +
>  /**
>   * struct drm_plane_state - mutable plane state
>   *
> @@ -152,6 +158,14 @@ struct drm_plane_state {
>          */
>         struct drm_solid_fill solid_fill;
>
> +       /*
> +        * @pixel_source:
> +        *
> +        * Source of pixel information for the plane. See
> +        * drm_plane_create_pixel_source_property() for more details.
> +        */
> +       enum drm_plane_pixel_source pixel_source;
> +
>         /**
>          * @alpha:
>          * Opacity of the plane with 0 as completely transparent and 0xffff as
> @@ -742,6 +756,13 @@ struct drm_plane {
>          */
>         struct drm_property *solid_fill_property;
>
> +       /*
> +        * @pixel_source_property:
> +        * Optional pixel_source property for this plane. See
> +        * drm_plane_create_pixel_source_property().
> +        */
> +       struct drm_property *pixel_source_property;
> +
>         /**
>          * @alpha_property:
>          * Optional alpha property for this plane. See
>
> --
> 2.41.0
>