On Mon, Mar 13, 2023 at 06:33:11PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> 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
> v3: Specify that value 0 is reserved for future use (basic idea from Jonas)
> Drop the note about typical hardware (Pekka)
>
> Cc: Simon Ser <contact@xxxxxxxxxxx>
> Cc: Jonas Ådahl <jadahl@xxxxxxxxxx>
> Cc: Daniel Stone <daniel@xxxxxxxxxxxxx>
> Cc: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> Acked-by: Harry Wentland <harry.wentland@xxxxxxx>
> Acked-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_mode_config.c | 7 ++++
> drivers/gpu/drm/drm_plane.c | 53 +++++++++++++++++++++++++++++++
> include/drm/drm_mode_config.h | 5 +++
> include/drm/drm_plane.h | 4 +++
> include/uapi/drm/drm_mode.h | 11 +++++++
> 5 files changed, 80 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..d2a6fdff1a57 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -140,6 +140,26 @@
> * 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.
> + *
> + * Note that property value 0 (ie. no blob) is reserved for potential
> + * future use. Current userspace is expected to ignore the property
> + * if the value is 0, and fall back to some other means (eg.
> + * &DRM_CAP_CURSOR_WIDTH and &DRM_CAP_CURSOR_HEIGHT) to determine
> + * the appropriate plane size to use.
Does this intend to mean userspace has the kernel's blessing on choosing
an arbitrary size as long as it's smaller than &DRM_CAP_CURSOR_WIDTH x
&DRM_CAP_CURSOR_HEIGHT?
It's a bit to vague for me to make a confident interpretation whether I
can, or whether I should pretend I didn't see SIZE_HINTS and apply the
old logic, meaning only using the exact cap size.
Jonas
> */
>
> static unsigned int drm_num_planes(struct drm_device *dev)
> @@ -1582,3 +1602,36 @@ 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.
> *
> --
> 2.39.2
>
