Re: [Intel-gfx] [PATCH v2 1/2] drm: Introduce plane SIZE_HINTS property

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 14, 2023 at 10:54:27AM +0100, Jonas Ådahl wrote:
> On Tue, Feb 14, 2023 at 11:25:56AM +0200, Ville Syrjälä wrote:
> > On Thu, Feb 09, 2023 at 03:16:23PM +0100, Jonas Ådahl wrote:
> > > On Wed, Feb 08, 2023 at 11:10:16PM +0200, Ville Syrjala wrote:
> > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > 
> > > > Add a new immutable plane property by which a plane can advertise
> > > > a handful of recommended plane sizes. This would be mostly exposed
> > > > by cursor planes as a slightly more capable replacement for
> > > > the DRM_CAP_CURSOR_WIDTH/HEIGHT caps, which can only declare
> > > > a one size fits all limit for the whole device.
> > > > 
> > > > Currently eg. amdgpu/i915/nouveau just advertize the max cursor
> > > > size via the cursor size caps. But always using the max sized
> > > > cursor can waste a surprising amount of power, so a better
> > > > stragey is desirable.
> > > > 
> > > > Most other drivers don't specify any cursor size at all, in
> > > > which case the ioctl code just claims that 64x64 is a great
> > > > choice. Whether that is actually true is debatable.
> > > > 
> > > > A poll of various compositor developers informs us that
> > > > blindly probing with setcursor/atomic ioctl to determine
> > > > suitable cursor sizes is not acceptable, thus the
> > > > introduction of the new property to supplant the cursor
> > > > size caps. The compositor will now be free to select a
> > > > more optimal cursor size from the short list of options.
> > > > 
> > > > Note that the reported sizes (either via the property or the
> > > > caps) make no claims about things such as plane scaling. So
> > > > these things should only really be consulted for simple
> > > > "cursor like" use cases.
> > > > 
> > > > v2: Try to add some docs
> > > > 
> > > > Cc: Simon Ser <contact@emersion.fr>
> > > > Cc: Jonas Ådahl <jadahl@redhat.com>
> > > > Cc: Daniel Stone <daniel@fooishbar.org>
> > > > Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
> > > > Acked-by: Harry Wentland <harry.wentland@amd.com>
> > > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_mode_config.c |  7 +++++
> > > >  drivers/gpu/drm/drm_plane.c       | 48 +++++++++++++++++++++++++++++++
> > > >  include/drm/drm_mode_config.h     |  5 ++++
> > > >  include/drm/drm_plane.h           |  4 +++
> > > >  include/uapi/drm/drm_mode.h       | 11 +++++++
> > > >  5 files changed, 75 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > > index 87eb591fe9b5..21860f94a18c 100644
> > > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > > +++ b/drivers/gpu/drm/drm_mode_config.c
> > > > @@ -374,6 +374,13 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
> > > >  		return -ENOMEM;
> > > >  	dev->mode_config.modifiers_property = prop;
> > > >  
> > > > +	prop = drm_property_create(dev,
> > > > +				   DRM_MODE_PROP_IMMUTABLE | DRM_MODE_PROP_BLOB,
> > > > +				   "SIZE_HINTS", 0);
> > > > +	if (!prop)
> > > > +		return -ENOMEM;
> > > > +	dev->mode_config.size_hints_property = prop;
> > > > +
> > > >  	return 0;
> > > >  }
> > > >  
> > > > diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> > > > index 24e7998d1731..ae51b1f83755 100644
> > > > --- a/drivers/gpu/drm/drm_plane.c
> > > > +++ b/drivers/gpu/drm/drm_plane.c
> > > > @@ -140,6 +140,21 @@
> > > >   *     DRM_FORMAT_MOD_LINEAR. Before linux kernel release v5.1 there have been
> > > >   *     various bugs in this area with inconsistencies between the capability
> > > >   *     flag and per-plane properties.
> > > > + *
> > > > + * SIZE_HINTS:
> > > > + *     Blob property which contains the set of recommended plane size
> > > > + *     which can used for simple "cursor like" use cases (eg. no scaling).
> > > > + *     Using these hints frees userspace from extensive probing of
> > > > + *     supported plane sizes through atomic/setcursor ioctls.
> > > > + *
> > > > + *     For optimal usage userspace should pick the smallest size
> > > > + *     that satisfies its own requirements.
> > > > + *
> > > > + *     The blob contains an array of struct drm_plane_size_hint.
> > > > + *
> > > > + *     Drivers should only attach this property to planes that
> > > > + *     support a very limited set of sizes (eg. cursor planes
> > > > + *     on typical hardware).
> > > 
> > > This is a bit awkward since problematic drivers would only expose
> > > this property if they are new enough.
> > > 
> > > A way to avoid this is for all new drivers expose this property, but
> > > special case the size 0x0 as "everything below the max limit goes". Then
> > > userspace can do (ignoring the missing cap fallback).
> > 
> > I don't think there are any drivers that need that.
> > So I'm thinking we can just ignore that for now.
> 
> None the less, userspace not seeing SIZE_HINTS will be required to
> indefinitely use the existing "old" behavior using the size cap as the
> buffer size with a fallback, and drivers without any size limitations
> that, i.e. details that are hard to express with a set of accepted
> sizes, will still use the inoptimal buffer sizes.
> 
> If I read [1] correctly, AMD has no particular size limitations other
> than a size limit, but without a SIZE_HINTS, userspace still needs to
> use the maximum size.

Simon pointed out they have pretty much the same exact limits as i915.
Ie. only a few power of two sizes, and stride must match width.

> 
> [1] https://gitlab.freedesktop.org/drm/intel/-/issues/7687#note_1760865
> 
> 
> Jonas
> 
> > 
> > > 
> > >     if (has(SIZE_HINTS))
> > >         size = figure_out_size(SIZE_HINTS,
> > > 	                       DRM_CAP_CURSOR_WIDTH,
> > > 			       DRM_CAP_CURSOR_HEIGHT,
> > > 			       preferred_size);
> > >     else
> > >         size = DRM_CAP_CURSOR_WIDTH x DRM_CAP_CURSOR_WIDTH;
> > > 
> > > With `figure_out_size()` knowing how to deal with 0x0 in the size hints
> > > to use `preferred_size` directly.
> > > 
> > > 
> > > Jonas
> > > 
> > > >   */
> > > >  
> > > >  static unsigned int drm_num_planes(struct drm_device *dev)
> > > > @@ -1582,3 +1597,36 @@ int drm_plane_create_scaling_filter_property(struct drm_plane *plane,
> > > >  	return 0;
> > > >  }
> > > >  EXPORT_SYMBOL(drm_plane_create_scaling_filter_property);
> > > > +
> > > > +/**
> > > > + * drm_plane_add_size_hint_property - create a size hint property
> > > > + *
> > > > + * @plane: drm plane
> > > > + * @hints: size hints
> > > > + * @num_hints: number of size hints
> > > > + *
> > > > + * Create a size hints property for the plane.
> > > > + *
> > > > + * RETURNS:
> > > > + * Zero for success or -errno
> > > > + */
> > > > +int drm_plane_add_size_hints_property(struct drm_plane *plane,
> > > > +				      const struct drm_plane_size_hint *hints,
> > > > +				      int num_hints)
> > > > +{
> > > > +	struct drm_device *dev = plane->dev;
> > > > +	struct drm_mode_config *config = &dev->mode_config;
> > > > +	struct drm_property_blob *blob;
> > > > +
> > > > +	blob = drm_property_create_blob(dev,
> > > > +					array_size(sizeof(hints[0]), num_hints),
> > > > +					hints);
> > > > +	if (IS_ERR(blob))
> > > > +		return PTR_ERR(blob);
> > > > +
> > > > +	drm_object_attach_property(&plane->base, config->size_hints_property,
> > > > +				   blob->base.id);
> > > > +
> > > > +	return 0;
> > > > +}
> > > > +EXPORT_SYMBOL(drm_plane_add_size_hints_property);
> > > > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> > > > index e5b053001d22..5bc8aed9b445 100644
> > > > --- a/include/drm/drm_mode_config.h
> > > > +++ b/include/drm/drm_mode_config.h
> > > > @@ -949,6 +949,11 @@ struct drm_mode_config {
> > > >  	 */
> > > >  	struct drm_property *modifiers_property;
> > > >  
> > > > +	/**
> > > > +	 * @size_hints_propertty: Plane SIZE_HINTS property.
> > > > +	 */
> > > > +	struct drm_property *size_hints_property;
> > > > +
> > > >  	/* cursor size */
> > > >  	uint32_t cursor_width, cursor_height;
> > > >  
> > > > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> > > > index 51291983ea44..1997d7d64b69 100644
> > > > --- a/include/drm/drm_plane.h
> > > > +++ b/include/drm/drm_plane.h
> > > > @@ -32,6 +32,7 @@
> > > >  #include <drm/drm_util.h>
> > > >  
> > > >  struct drm_crtc;
> > > > +struct drm_plane_size_hint;
> > > >  struct drm_printer;
> > > >  struct drm_modeset_acquire_ctx;
> > > >  
> > > > @@ -945,5 +946,8 @@ drm_plane_get_damage_clips(const struct drm_plane_state *state);
> > > >  
> > > >  int drm_plane_create_scaling_filter_property(struct drm_plane *plane,
> > > >  					     unsigned int supported_filters);
> > > > +int drm_plane_add_size_hints_property(struct drm_plane *plane,
> > > > +				      const struct drm_plane_size_hint *hints,
> > > > +				      int num_hints);
> > > >  
> > > >  #endif
> > > > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > > > index 46becedf5b2f..9d7c5967264f 100644
> > > > --- a/include/uapi/drm/drm_mode.h
> > > > +++ b/include/uapi/drm/drm_mode.h
> > > > @@ -849,6 +849,17 @@ struct drm_color_lut {
> > > >  	__u16 reserved;
> > > >  };
> > > >  
> > > > +/**
> > > > + * struct drm_plane_size_hint - Plane size hints
> > > > + *
> > > > + * The plane SIZE_HINTS property blob contains an
> > > > + * array of struct drm_plane_size_hint.
> > > > + */
> > > > +struct drm_plane_size_hint {
> > > > +	__u16 width;
> > > > +	__u16 height;
> > > > +};
> > > > +
> > > >  /**
> > > >   * struct hdr_metadata_infoframe - HDR Metadata Infoframe Data.
> > > >   *
> > > > -- 
> > > > 2.39.1
> > > > 
> > 
> > -- 
> > Ville Syrjälä
> > Intel
> > 

-- 
Ville Syrjälä
Intel