[PATCH] RFC: drm/drm_plane: Expose the plane capability and interoperability

[Dmitry Baryshkov]

On Mon, Jul 29, 2024 at 04:59:14AM GMT, Murthy, Arun R wrote:
> Gentle Reminder!
> Any comments?

First of all, the format is underdocumented. Second, there is a usual
requirement for new uAPI: please provide a pointer to IGT patch and to
the userspace utilising the property.

> 
> Thanks and Regards,
> Arun R Murthy
> --------------------
> 
> > -----Original Message-----
> > From: Murthy, Arun R <arun.r.murthy at intel.com>
> > Sent: Tuesday, July 9, 2024 1:17 PM
> > To: dri-devel at lists.freedesktop.org; intel-gfx at lists.freedesktop.org
> > Cc: Murthy, Arun R <arun.r.murthy at intel.com>
> > Subject: [PATCH] RFC: drm/drm_plane: Expose the plane capability and
> > interoperability
> > 
> > Each plane has its own capability or interoperability based on the harware
> > restrictions. If this is exposed to the user, then user can read it once on boot
> > and store this. Later can be used as a lookup table to check a corresponding
> > capability is supported by plane then only go ahead with the framebuffer
> > creation/calling atomic_ioctl.
> > 
> > For Ex: There are few restiction as to async flip doesnt support all the
> > formats/modifiers. Similar restrictions on scaling. With the availabililty of this
> > info to user, failures in atomic_check can be avoided as these are more the
> > hardware capabilities.
> > 
> > There are two options on how this can be acheived.
> > Option 1:
> > 
> > Add a new element to struct drm_mode_get_plane that holds the addr to the
> > array of a new struct. This new struct consists of the formats supported and the
> > corresponding plane capabilities.
> > 
> > Option 2:
> > 
> > These can be exposed to user as a plane property so that the user can get to
> > know the limitation ahead and avoid failures in atomic_check.
> > 
> > Usually atomic_get_property is controlled over the state struct for the
> > parameters/elements that can change. But here these capabilities or the
> > interoperabilities are rather hardware restrictions and wont change over flips.
> > Hence having as a plane_property may not make much sense.
> > On the other hand, Option 1 include changes in the uapi struct
> > drm_mode_get_plane. Shouldnt have impact on backward compatibility, but if
> > userspace has some implementation so as to check the size of the struct, then it
> > might a challenge.
> > 
> > Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_uapi.c |  3 +++
> >  include/drm/drm_plane.h           |  8 ++++++++
> >  include/uapi/drm/drm_mode.h       | 20 ++++++++++++++++++++
> >  3 files changed, 31 insertions(+)
> > 
> > =============Option 2========================
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c
> > b/drivers/gpu/drm/drm_atomic_uapi.c
> > index 22bbb2d83e30..b46177d5fc8c 100644
> > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > @@ -631,6 +631,9 @@ drm_atomic_plane_get_property(struct drm_plane
> > *plane,
> >  		*val = state->hotspot_x;
> >  	} else if (property == plane->hotspot_y_property) {
> >  		*val = state->hotspot_y;
> > +	} else if (property == config->prop_plane_caps) {
> > +		*val = (state->plane_caps) ?
> > +			state->plane_caps->base.id : 0;
> >  	} else {
> >  		drm_dbg_atomic(dev,
> >  			       "[PLANE:%d:%s] unknown property
> > [PROP:%d:%s]\n", diff --git a/include/drm/drm_plane.h
> > b/include/drm/drm_plane.h index dd718c62ac31..dfe931677d0a 100644
> > --- a/include/drm/drm_plane.h
> > +++ b/include/drm/drm_plane.h
> > @@ -260,6 +260,14 @@ struct drm_plane_state {
> >  	 * flow.
> >  	 */
> >  	bool color_mgmt_changed : 1;
> > +
> > +	/**
> > +	 * @plane_caps:
> > +	 *
> > +	 * Blob representing plane capcabilites and interoperability.
> > +	 * This element is a pointer to the array of struct drm_format_blob.
> > +	 */
> > +	struct drm_property_blob *plane_caps;
> >  };
> > 
> >  static inline struct drm_rect
> > 
> > =============Option 1========================
> > 
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index d390011b89b4..0b5c1b65ef63 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -312,6 +312,20 @@ struct drm_mode_set_plane {
> >  	__u32 src_w;
> >  };
> > 
> > +#define DRM_FORMAT_PLANE_CAP_LINEAR_TILE	BIT(0)
> > +#define DRM_FORMAT_PLANE_CAP_X_TILE		BIT(1)
> > +#define DRM_FORMAT_PLANE_CAP_Y_TILE		BIT(2)
> > +#define DRM_FORMAT_PLANE_CAP_Yf_TILE		BIT(3)
> > +#define DRM_FORMAT_PLANE_CAP_ASYNC_FLIP		BIT(4)
> > +#define DRM_FORMAT_PLANE_CAP_FBC		BIT(5)
> > +#define DRM_FORMAT_PLANE_CAP_RC			BIT(6)
> > +
> > +struct drm_format_blob {
> > +	__u64 modifier;
> > +	__u32 plane_caps;
> > +
> > +};
> > +
> >  /**
> >   * struct drm_mode_get_plane - Get plane metadata.
> >   *
> > @@ -355,6 +369,12 @@ struct drm_mode_get_plane {
> >  	 * supported by the plane. These formats do not require modifiers.
> >  	 */
> >  	__u64 format_type_ptr;
> > +	/**
> > +	 * @ format_blob_ptr: Pointer to the array of struct drm_format_blob.
> > +	 * Specify the plane capabilites/restrictions w.r.t tiling/sync-async
> > +	 * flips etc
> > +	 */
> > +	__u64 format_blob_ptr;
> >  };
> > 
> >  struct drm_mode_get_plane_res {
> > --
> > 2.25.1
> 

-- 
With best wishes
Dmitry