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

Pekka Paalanen
2023-06-30T08:27:33Z

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On Fri, 30 Jun 2023 03:42:28 +0300
Dmitry Baryshkov <dmitry.baryshkov@linaro.org> wrote:

> On 30/06/2023 03:25, Jessica Zhang 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.
>
> I think, this should come before the solid fill property addition. First
> you tell that there is a possibility to define other pixel sources, then
> additional sources are defined.

Hi,

that would be logical indeed.

> >
> > 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) {
>
> I think, it was pointed out in the discussion that drm_mode_setplane()
> (a pre-atomic IOCTL to turn the plane on and off) should also reset
> pixel_source to FB.
>
> > @@ -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.

Other sources than the selected one are ignored?

> > + *
> > + * Possible values:

Wouldn't hurt to explicitly mention here that this is an enum.

> > + *
> > + * "FB":
> > + * Framebuffer source
> > + *
> > + * "COLOR":
> > + * solid_fill source

I think these two should be more explicit. Framebuffer source is the
usual source from the property "FB_ID". Solid fill source comes from
the property "solid_fill".

Why "COLOR" and not, say, "SOLID_FILL"?

> > + *
> > * 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).
>
> I'd say this is too strong. I'd suggest either renaming this to
> extra_sources (mentioning that FB is enabled for all the planes) or
> allowing any source bitmask (mentioning that FB should be enabled by the
> caller, unless there is a good reason not to do so).

Right. I don't see any problem with having planes of type OVERLAY that
support only solid_fill and no FB. Planes of type PRIMARY and CURSOR I
would expect to always support at least FB.

Atomic userspace is prepared to have an OVERLAY plane fail for any
arbitrary reason. Legacy userspace probably should not ever see a plane
that does not support FB.

> > + *
> > + * 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
> > + *
> > + * 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);
>
>
> static const?
>
> > + 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",

Shouldn't this be an atomic prop?

> > + 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))
>
> test_bit?
>
> > + continue;
> > +
> > + ret = drm_property_add_enum(prop, enum_list[i].type, enum_list[i].name);
> > +
>
> No need for an empty line in such cases. Please drop it.
>
> > + 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
> > +};

Just to be very clear that I'm not confusing you with my comment about
UAPI headers in the previous patch, this enum is already in a good
place. It does not belong in a UAPI header, because userspace
recognises enum values by the name string.

Thanks,
pq

> > +
> > /**
> > * 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
> >
>

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