On Tue, Feb 14, 2023 at 01:19:51PM +0200, Ville Syrjälä wrote: > On Tue, Feb 14, 2023 at 12:01:49PM +0100, Jonas Ådahl wrote: > > On Tue, Feb 14, 2023 at 12:28:44PM +0200, Ville Syrjälä wrote: > > > 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@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 > > > > > > > > > > > > > > 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> > > > > > > > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > > --- > > > > > > > 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. > > > > How about various ARM drivers, where the cursor plane is a regular > > overlay plane with an artificial 'cursor' stamp on it? > > They don't even bother with the size cap currently. So the > generic ioctl code currently just decides that 64x64 is good > enough for them. > > > > > Either way, the documentation creates an impossible expectation - > > drivers, existing of future, that does not "support for a very limited > > set of sizes" but actually any size below a limit, can't communicate to > > userspace that it can handle cursor buffers with an arbitrary sizes, > > without userspace breaking on todays kernels. > > I don't see how anything would break. You just won't get a 100% > optimal result potentially if you don't declare any smaller > sizes. And I think we can always specify that magic 0x0 value > later (or a new cap/etc) should an actual user for it appear. Or maybe better than the 0x0 magic value inside the blob would be to just have the property with value 0 (ie. no blob at all)? -- Ville Syrjälä Intel
