Message-ID: <20230630112708.4d3a08a7@eldfell>
Date:   Fri, 30 Jun 2023 11:27:08 +0300
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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, sebastian.wick@...hat.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 v4 2/7] drm: Introduce pixel_source DRM plane
 property

On Fri, 30 Jun 2023 03:42:28 +0300
Dmitry Baryshkov <dmitry.baryshkov@...aro.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@...cinc.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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