linux-kernel - Re: [PATCH RFC v5 02/10] drm: Introduce solid fill DRM plane property

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Message-ID: <20230818135133.3fdeddba@eldfell>
Date:   Fri, 18 Aug 2023 13:51:33 +0300
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Sebastian Wick <sebastian.wick@...hat.com>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        quic_abhinavk@...cinc.com, contact@...rsion.fr,
        laurent.pinchart@...asonboard.com, ville.syrjala@...ux.intel.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        wayland-devel@...ts.freedesktop.org
Subject: Re: [PATCH RFC v5 02/10] drm: Introduce solid fill DRM plane
 property

On Fri, 4 Aug 2023 16:59:00 +0300
Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:

> On Fri, 4 Aug 2023 at 16:44, Sebastian Wick <sebastian.wick@...hat.com> wrote:
> >
> > On Fri, Aug 4, 2023 at 3:27 PM Dmitry Baryshkov
> > <dmitry.baryshkov@...aro.org> wrote:  
> > >
> > > On Fri, 28 Jul 2023 at 20:03, Jessica Zhang <quic_jesszhan@...cinc.com> wrote:  
> > > >
> > > > Document and add support for solid_fill property to drm_plane. In
> > > > addition, add support for setting and getting the values for solid_fill.
> > > >
> > > > To enable solid fill planes, userspace must assign a property blob to
> > > > the "solid_fill" plane property containing the following information:
> > > >
> > > > struct drm_mode_solid_fill {
> > > >         u32 version;
> > > >         u32 r, g, b;
> > > > };
> > > >
> > > > Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_atomic_state_helper.c |  9 +++++
> > > >  drivers/gpu/drm/drm_atomic_uapi.c         | 55 +++++++++++++++++++++++++++++++
> > > >  drivers/gpu/drm/drm_blend.c               | 30 +++++++++++++++++
> > > >  include/drm/drm_blend.h                   |  1 +
> > > >  include/drm/drm_plane.h                   | 35 ++++++++++++++++++++
> > > >  include/uapi/drm/drm_mode.h               | 24 ++++++++++++++
> > > >  6 files changed, 154 insertions(+)
> > > >  
> > >
> > > [skipped most of the patch]
> > >  
> > > > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > > > index 43691058d28f..53c8efa5ad7f 100644
> > > > --- a/include/uapi/drm/drm_mode.h
> > > > +++ b/include/uapi/drm/drm_mode.h
> > > > @@ -259,6 +259,30 @@ struct drm_mode_modeinfo {
> > > >         char name[DRM_DISPLAY_MODE_LEN];
> > > >  };
> > > >
> > > > +/**
> > > > + * struct drm_mode_solid_fill - User info for solid fill planes
> > > > + *
> > > > + * This is the userspace API solid fill information structure.
> > > > + *
> > > > + * Userspace can enable solid fill planes by assigning the plane "solid_fill"
> > > > + * property to a blob containing a single drm_mode_solid_fill struct populated with an RGB323232
> > > > + * color and setting the pixel source to "SOLID_FILL".
> > > > + *
> > > > + * For information on the plane property, see drm_plane_create_solid_fill_property()
> > > > + *
> > > > + * @version: Version of the blob. Currently, there is only support for version == 1
> > > > + * @r: Red color value of single pixel
> > > > + * @g: Green color value of single pixel
> > > > + * @b: Blue color value of single pixel
> > > > + */
> > > > +struct drm_mode_solid_fill {
> > > > +       __u32 version;
> > > > +       __u32 r;
> > > > +       __u32 g;
> > > > +       __u32 b;  
> > >
> > > Another thought about the drm_mode_solid_fill uABI. I still think we
> > > should add alpha here. The reason is the following:
> > >
> > > It is true that we have  drm_plane_state::alpha and the plane's
> > > "alpha" property. However it is documented as "the plane-wide opacity
> > > [...] It can be combined with pixel alpha. The pixel values in the
> > > framebuffers are expected to not be pre-multiplied by the global alpha
> > > associated to the plane.".
> > >
> > > I can imagine a use case, when a user might want to enable plane-wide
> > > opacity, set "pixel blend mode" to "Coverage" and then switch between
> > > partially opaque framebuffer and partially opaque solid-fill without
> > > touching the plane's alpha value.  
> >
> > The only reason I see against this is that there might be some
> > hardware which supports only RGB but not alpha on planes and they
> > could then not use this property.  
> 
> Fair enough.
> 
> > Maybe another COLOR_FILL enum value
> > with alpha might be better? Maybe just doing the alpha via the alpha
> > property is good enough.  
> 
> One of our customers has a use case for setting the opaque solid fill,
> while keeping the plane's alpha intact.

Could you explain more about why they must keep plane alpha intact
instead of reprogramming everything with atomic? Is there some
combination that just cannot reach the same end result via userspace
manipulation of the solid fill values with plane alpha?

Or is it a matter of userspace architecture where you have independent
components responsible for different KMS property values?


Thanks,
pq

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