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

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

On Wed, Feb 08, 2023 at 03:03:49PM +0200, Ville Syrjälä wrote:
> On Wed, Feb 08, 2023 at 02:13:12PM +0200, Pekka Paalanen wrote:
> > On Wed,  8 Feb 2023 06:09:10 +0200
> > Ville Syrjala <ville.syrjala@linux.intel.com> 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.
> > > 
> > > 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>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_mode_config.c |  7 +++++++
> > >  drivers/gpu/drm/drm_plane.c       | 33 +++++++++++++++++++++++++++++++
> > >  include/drm/drm_mode_config.h     |  5 +++++
> > >  include/drm/drm_plane.h           |  4 ++++
> > >  include/uapi/drm/drm_mode.h       |  5 +++++
> > >  5 files changed, 54 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..d0a277f4be1f 100644
> > > --- a/drivers/gpu/drm/drm_plane.c
> > > +++ b/drivers/gpu/drm/drm_plane.c
> > > @@ -1582,3 +1582,36 @@ 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..ed9f6938dca1 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_property: 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..4f0551d7f481 100644
> > > --- a/include/uapi/drm/drm_mode.h
> > > +++ b/include/uapi/drm/drm_mode.h
> > > @@ -849,6 +849,11 @@ struct drm_color_lut {
> > >  	__u16 reserved;
> > >  };
> > >  
> > > +struct drm_plane_size_hint {
> > > +	__u16 width;
> > > +	__u16 height;
> > > +};
> > 
> > Hi Ville,
> > 
> > uAPI documentation is missing.
> > 
> > When there is just a single recommended size listed, userspace has it
> > easy: allocate a pair of DRM dumb buffers for each active CRTC, do
> > atomic test commits with those, and if the test succeeds, copy in the
> > pixels and fill the padding.
> > 
> > What if we have multiple or a huge number of possible sizes? Probably
> > for each KMS reconfiguration cycle (which could be up to every refresh
> > cycle) userspace would need to allocate a new dumb buffer to have the
> > right size, and then test. Is that something we can actually afford to
> > do? I don't know.
> 
> Why would you allocate multiple buffers? Just allocate one
> with the max size and then you can reuse it at any smaller
> size as needed.

Unfortunately the use of gbm here means the stride would
be wrong for the smaller sizes. So I guess a different
buffer for each size is what you need to do. Unless you
can just ignore the original stride when filling the buffer.

> 
> > 
> > Therefore maybe this proposal is a good compromise. The driver lists
> > *few* sizes that are roughly equally likely to work, that is, if the
> > cursor plane does not work, it's not because of the size. Userspace
> > pre-allocates DRM dumb buffers for each size. When attempting to use a
> > cursor plane, userspace picks the smallest size that suffices, and tests
> > only with that.
> 
> Yeah, don't see why you ever retry multiple times with increased
> cursor size. If the small size doesn't work then surely the
> larger size won't either (larger size requiring more hw resources
> to operate).
> 
> > 
> > Seems fine to me. The uAPI docs should explain what userspace is
> > expected to do with it.
> > 
> > 
> > Thanks,
> > pq
> > 
> > > +
> > >  /**
> > >   * struct hdr_metadata_infoframe - HDR Metadata Infoframe Data.
> > >   *
> 
> -- 
> Ville Syrjälä
> Intel

-- 
Ville Syrjälä
Intel