[PATCH v3 1/8] drm/blend: Add a generic alpha property

[Maxime Ripard]

On Mon, Feb 19, 2018 at 10:58:40PM +0100, Daniel Vetter wrote:
> On Mon, Feb 19, 2018 at 9:19 PM, Laurent Pinchart
> <laurent.pinchart at ideasonboard.com> wrote:
> > Hi Ville,
> >
> > On Friday, 16 February 2018 20:20:41 EET Ville Syrjälä wrote:
> >> On Fri, Feb 16, 2018 at 06:39:29PM +0100, Maxime Ripard wrote:
> >> > Some drivers duplicate the logic to create a property to store a per-plane
> >> > alpha.
> >> >
> >> > This is especially useful if we ever want to support extra protocols for
> >> > Wayland like:
> >> > https://lists.freedesktop.org/archives/wayland-devel/2017-August/034741.ht
> >> > ml
> >> >
> >> > Let's create a helper in order to move that to the core.
> >> >
> >> > Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >> > Reviewed-by: Boris Brezillon <boris.brezillon at bootlin.com>
> >> > Signed-off-by: Maxime Ripard <maxime.ripard at bootlin.com>
> >> > ---
> >> >
> >> >  Documentation/gpu/kms-properties.csv |  2 +-
> >> >  drivers/gpu/drm/drm_atomic.c         |  4 ++++-
> >> >  drivers/gpu/drm/drm_atomic_helper.c  |  4 ++++-
> >> >  drivers/gpu/drm/drm_blend.c          | 32 +++++++++++++++++++++++++++++-
> >> >  include/drm/drm_blend.h              |  1 +-
> >> >  include/drm/drm_plane.h              |  6 +++++-
> >> >  6 files changed, 48 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/Documentation/gpu/kms-properties.csv
> >> > b/Documentation/gpu/kms-properties.csv index 927b65e14219..25ad3503d663
> >> > 100644
> >> > --- a/Documentation/gpu/kms-properties.csv
> >> > +++ b/Documentation/gpu/kms-properties.csv
> >> > @@ -99,5 +99,5 @@ radeon,DVI-I,“coherent”,RANGE,"Min=0,
> >> > Max=1",Connector,TBD>
> >> >  ,,"""underscan vborder""",RANGE,"Min=0, Max=128",Connector,TBD
> >> >  ,Audio,“audio”,ENUM,"{ ""off"", ""on"", ""auto"" }",Connector,TBD
> >> >  ,FMT Dithering,“dither”,ENUM,"{ ""off"", ""on"" }",Connector,TBD
> >> >
> >> > -rcar-du,Generic,"""alpha""",RANGE,"Min=0, Max=255",Plane,TBD
> >> > +,,"""alpha""",RANGE,"Min=0, Max=Driver dependant",Plane,Opacity of the
> >> > plane from transparent (0) to fully opaque (MAX). If this property is set
> >> > to a value different than max, and that the pixel will define an alpha
> >> > component, the property will have precendance and the pixel value will be
> >> > ignored.
> 
> Please don't document new properties in that csv file, it's an
> unreadable mess. Instead follow how we document standardized
> properties nowadays in full-blown sections. For plane blending we
> have:
> 
> https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#plane-composition-properties

Ack

> >> > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> >> > index 8185e3468a23..5a6f29524f12 100644
> >> > --- a/include/drm/drm_plane.h
> >> > +++ b/include/drm/drm_plane.h
> >> > @@ -42,6 +42,7 @@ struct drm_modeset_acquire_ctx;
> >> >   * plane (in 16.16)
> >> >   * @src_w: width of visible portion of plane (in 16.16)
> >> >   * @src_h: height of visible portion of plane (in 16.16)
> >> > + * @alpha: opacity of the plane
> >> >   * @rotation: rotation of the plane
> >> >   * @zpos: priority of the given plane on crtc (optional)
> >> >   * Note that multiple active planes on the same crtc can have an
> >> >   identical
> >> > @@ -105,6 +106,9 @@ struct drm_plane_state {
> >> >     uint32_t src_x, src_y;
> >> >     uint32_t src_h, src_w;
> >> >
> >> > +   /* Plane opacity */
> >> > +   u8 alpha;
> >>
> >> We may want to make that u16. The general we expect 16bpc for most color
> >> related things, but since this is a range prop I suppose we should just
> >> expose the actual hardware range. But making it u16 might avoid some head
> >> scratching for the first person to have hardware with higher precision.
> >> Either that or we should make the prop creation fail if the driver asks
> >> for more bits than we have in the state.
> >
> > I'm tempted to go one step further and always make the alpha property 16-bits
> > wide for new users (we can't do so for existing users as it could break
> > userspace), and let drivers convert that internally to the range they need.
> > There could however be drawbacks I don't foresee.
> 
> I think scaling the range to match the hw is the most sensible (yes
> I'm flip-flopping around here). And once someone needs more than u8,
> we can extend the internal representation easily. The external
> representation in the property is an u64, that /should/ be enough for
> the next few years :-)

Just to make sure we're on the same page, you want to keep the u8, and
if the hardware uses say an u16, the driver for that hardware will do
the upscaling?

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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