Re: [PATCH RFC 13/25] drm: Add VRR target frame rate properties

[Vidith Madhu <vmadhu@nvidia.com>]

On Tue, 29 Sep 2026, Nicolas Frattaroli wrote:

> On Tuesday, 29 September 2026 21:16:57 Central European Summer Time Vidith Madhu wrote:
> > 
> > On Mon, 21 Sep 2026, Nicolas Frattaroli wrote:
> > 
> > > Userspace may wish to set a target frame rate for the Variable Refresh
> > > Rate mechanism. There are multiple possible ways such a target could be
> > > communicated.
> > > 
> > > It's desirable for userspace to not only set a fixed target, but a
> > > target range within which VRR may operate. This is because even if a
> > > sink advertises a certain range as supported, said range may not be the
> > > ideal range to use, as numbers on the extreme end of the range may
> > > induce flickering or other glitches.
> > My understanding is that flicker may also happen if the refresh rate 
> > fluctuates significantly within the sinks' range, although I don't know 
> > how common this is in practice. I would imagine these frame range limits
> > would also be useful there to "dampen" the fluctuation.
> 
> Theoretically, the HDMI E-EDID extension does have a field to specify the
> maximum change in VRR per frame that's allowed without visual issues, but
> I'm not sure if any display sets this to a sensible value because such
> issues can range from the mentioned brightness inconsistencies to pictures
> that are positioned/scaled wrong in the vertical axis. In the absence of
> evidence that this flag is used usefully, I've not implemented it in my
> HDMI state helper implementation of VRR so far.
> 
> > In any case, if we expect userspace to use the frame range limits for the 
> > purpose of flicker avoidance, it may make sense to expose a read-only 
> > connector property for whether the display is susceptible to such
> > flickering. For example, NVIDIA G-SYNC monitors are resilient to this and
> > it would hinder the user experience to unnecessarily impose such a limit.
> 
> Short of keeping a whole quirks database, I don't think we can solve this
> generally. The idea I've been working off of is that the compositor has
> settings to explicitly specify such limits, much like e.g. KDE has a
> checkbox in the monitor settings right now to enable/disable VRR for a
> specific monitor, or weston.ini has an output config option. The user can
> then impose a limit if they do notice issues with their particular monitor
> in their particular use-case.
> 
> I can see adding an additional property to communicate a specific flavor
> of VRR implementation, especially if this is non-trivial for userspace
> to figure out otherwise, e.g. because some displays may use several and
> the driver picks the best one.
Right, this is what I had in mind. It would be nice if drivers at least 
had the ability to supply a hint on what the VRR policy should be to 
userspace.

Thanks,
Vidith
> 
> I do encourage additional fleshing out of the problem space we're trying
> to address here though, so if anyone or their loved one is entitled to
> compensation for the hurt caused by flickery VRR, I'd love to hear
> specifics. I have experienced it with dark gaming content on a
> ASUS ROG STRIX XG27AQDMG connected over DisplayPort to an AMD GPU. At the
> same time, I've yet to notice anything on that same monitor when
> displaying VRR content over HDMI from a RK3588 SBC, but that might be
> because SuperTuxKart happens to run too consistently frame-to-frame to
> trigger it.
> 
> Kind regards,
> Nicolas Frattaroli
> 
> > >
> > > There's four choices to how one bracketing value for the target range
> > > could be communicated:
> > > 1. Target frame rate in something like millihertz
> > > 2. Target frame period in something like usecs
> > > 3. Target vtotal value
> > > 4. Target frame rate as a fraction expressed by two integers
> > > 
> > > Choice 1 is unpleasant as it would introduce some amount of rounding to
> > > common broadcast framerates like 24/1.001, which seems minor except that
> > > exact matches to standard framerates would rely on making all userspace
> > > and kernel agree on a specific method of rounding. This is sure to go
> > > wrong, so is disqualified.
> > > 
> > > Choice 2 has the same problem as 1, with the added complication that
> > > the EDID's VRR range is expressed in frames per second, and other HDMI
> > > features express things in frames per second as well, which would
> > > require possibly imprecise computations.
> > > 
> > > Choice 3 is disqualified as mechanisms other than VRR, such as FVA, may
> > > also modify the vtotal value. Additionally, it has the same drawbacks of
> > > choice 2 and 1.
> > > 
> > > Choice 4 is therefore what's implemented. The frame rate 24/1.001Hz, for
> > > example, is expressed as nominator=24000 and denominator=1001. As there
> > > is both a minimum and a maximum, there are 4 properties in total: two
> > > numerators, and two denominators. A fixed rate with no variability is
> > > expressed by setting the minimum fractional and the maximum fractional
> > > properties to the same value.
> > > 
> > > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> > > ---
> > >  drivers/gpu/drm/drm_atomic_uapi.c | 24 +++++++++++++++++++++
> > >  drivers/gpu/drm/drm_connector.c   | 45 +++++++++++++++++++++++++++++++++++++++
> > >  drivers/gpu/drm/drm_crtc.c        |  8 +++++++
> > >  drivers/gpu/drm/drm_mode_config.c | 20 +++++++++++++++++
> > >  include/drm/drm_crtc.h            |  4 ++++
> > >  include/drm/drm_mode_config.h     | 45 +++++++++++++++++++++++++++++++++++++++
> > >  6 files changed, 146 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> > > index 1eebcf6f5e05..c9eb01d740b3 100644
> > > --- a/drivers/gpu/drm/drm_atomic_uapi.c
> > > +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> > > @@ -420,6 +420,22 @@ static int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
> > >  		return ret;
> > >  	} else if (property == config->prop_vrr_enabled) {
> > >  		state->vrr_enabled = val;
> > > +	} else if (property == config->prop_vrr_min_numerator) {
> > > +		if (val > U32_MAX)
> > > +			return -EINVAL;
> > > +		state->vrr_state.vrr_min_n = val;
> > > +	} else if (property == config->prop_vrr_min_denominator) {
> > > +		if (val > U32_MAX)
> > > +			return -EINVAL;
> > > +		state->vrr_state.vrr_min_d = val;
> > > +	} else if (property == config->prop_vrr_max_numerator) {
> > > +		if (val > U32_MAX)
> > > +			return -EINVAL;
> > > +		state->vrr_state.vrr_max_n = val;
> > > +	} else if (property == config->prop_vrr_max_denominator) {
> > > +		if (val > U32_MAX)
> > > +			return -EINVAL;
> > > +		state->vrr_state.vrr_max_d = val;
> > >  	} else if (property == config->degamma_lut_property) {
> > >  		const size_t elem_size = sizeof(struct drm_color_lut);
> > >  		u64 lut_size;
> > > @@ -505,6 +521,14 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
> > >  		*val = (state->mode_blob) ? state->mode_blob->base.id : 0;
> > >  	else if (property == config->prop_vrr_enabled)
> > >  		*val = state->vrr_enabled;
> > > +	else if (property == config->prop_vrr_min_numerator)
> > > +		*val = state->vrr_state.vrr_min_n;
> > > +	else if (property == config->prop_vrr_min_denominator)
> > > +		*val = state->vrr_state.vrr_min_d;
> > > +	else if (property == config->prop_vrr_max_numerator)
> > > +		*val = state->vrr_state.vrr_max_n;
> > > +	else if (property == config->prop_vrr_max_denominator)
> > > +		*val = state->vrr_state.vrr_max_d;
> > >  	else if (property == config->degamma_lut_property)
> > >  		*val = (state->degamma_lut) ? state->degamma_lut->base.id : 0;
> > >  	else if (property == config->ctm_property)
> > > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > > index fc7d9fcf9d9f..5c07bd221977 100644
> > > --- a/drivers/gpu/drm/drm_connector.c
> > > +++ b/drivers/gpu/drm/drm_connector.c
> > > @@ -2579,6 +2579,51 @@ EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
> > >   *
> > >   *	The driver may place further restrictions within these minimum
> > >   *	and maximum bounds.
> > > + *
> > > + * VRR Limiter/Target Properties
> > > + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > + *
> > > + * The ``VRR_{MIN,MAX}_{NUMERATOR,DENOMINATOR}`` properties expose a mechanism
> > > + * through which userspace can control the desired range of refresh rates in
> > > + * which VRR is allowed to operate. Each rate is expressed as a
> > > + * numerator/denominator fraction of refresh rates in Hz, allowing for rational
> > > + * target rates like 24/1.001 Hz with no loss of precision or ambiguity.
> > > + *
> > > + * If the minimum and maximum rate are set to the same value (and not 0), they
> > > + * are understood as a fixed target rate. This is especially useful for media
> > > + * playback, where the content's frame rate is both constant and known in
> > > + * advance. In such cases, a refresh rate that is not an integer multiple of the
> > > + * content's frame rate will introduce judder, since not every frame is
> > > + * displayed for the same amount of time. A modeset of the display with a
> > > + * compatible rate may in those cases be either undesirable or impossible, but
> > > + * the rate can still effectively be reached through VRR.
> > > + *
> > > + * .. _VRR-MIN-NUMERATOR:
> > > + *
> > > + * "VRR_MIN_NUMERATOR":
> > > + *	Default &drm_crtc integer property forming the numerator of a
> > > + *	numerator/denominator pair of a frame rate to set as the minimum VRR
> > > + *	target rate. Set to 0 to disable.
> > > + *
> > > + * "VRR_MIN_DENOMINATOR":
> > > + *	Default &drm_crtc integer property forming the denominator of a
> > > + *	numerator/denominator pair of a frame rate to set as the minimum VRR
> > > + *	target rate. If :ref:`VRR_MIN_NUMERATOR <VRR-MIN-NUMERATOR>` is not
> > > + *	zero, it must be non-zero.
> > > + *	Otherwise, must also be zero.
> > > + *
> > > + * .. _VRR-MAX-NUMERATOR:
> > > + *
> > > + * "VRR_MAX_NUMERATOR":
> > > + *	Default &drm_crtc integer property forming the numerator of a
> > > + *	numerator/denominator pair of a frame rate to set as the maximum VRR
> > > + *	target rate. Set to 0 to disable.
> > > + *
> > > + * "VRR_MAX_DENOMINATOR":
> > > + *	Default &drm_crtc integer property forming the denominator of a
> > > + *	numerator/denominator pair of a frame rate to set as the maximum VRR
> > > + *	target rate. If :ref:`VRR_MAX_NUMERATOR <VRR-MAX-NUMERATOR>` is not
> > > + *	zero, it must be non-zero. Otherwise, must also be zero.
> > >   */
> > >  
> > >  /**
> > > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > > index 63ead8ba6756..9244fbf97029 100644
> > > --- a/drivers/gpu/drm/drm_crtc.c
> > > +++ b/drivers/gpu/drm/drm_crtc.c
> > > @@ -322,6 +322,14 @@ static int __drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *
> > >  					   config->prop_out_fence_ptr, 0);
> > >  		drm_object_attach_property(&crtc->base,
> > >  					   config->prop_vrr_enabled, 0);
> > > +		drm_object_attach_property(&crtc->base,
> > > +					   config->prop_vrr_min_numerator, 0);
> > > +		drm_object_attach_property(&crtc->base,
> > > +					   config->prop_vrr_min_denominator, 0);
> > > +		drm_object_attach_property(&crtc->base,
> > > +					   config->prop_vrr_max_numerator, 0);
> > > +		drm_object_attach_property(&crtc->base,
> > > +					   config->prop_vrr_max_denominator, 0);
> > >  	}
> > >  
> > >  	return 0;
> > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > index 48a56f23dadb..da967d60f832 100644
> > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > +++ b/drivers/gpu/drm/drm_mode_config.c
> > > @@ -535,6 +535,26 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
> > >  		return -ENOMEM;
> > >  	dev->mode_config.prop_vrr_enabled = prop;
> > >  
> > > +	prop = drm_property_create_range(dev, 0, "VRR_MIN_NUMERATOR", 0, U32_MAX);
> > > +	if (!prop)
> > > +		return -ENOMEM;
> > > +	dev->mode_config.prop_vrr_min_numerator = prop;
> > > +
> > > +	prop = drm_property_create_range(dev, 0, "VRR_MIN_DENOMINATOR", 0, U32_MAX);
> > > +	if (!prop)
> > > +		return -ENOMEM;
> > > +	dev->mode_config.prop_vrr_min_denominator = prop;
> > > +
> > > +	prop = drm_property_create_range(dev, 0, "VRR_MAX_NUMERATOR", 0, U32_MAX);
> > > +	if (!prop)
> > > +		return -ENOMEM;
> > > +	dev->mode_config.prop_vrr_max_numerator = prop;
> > > +
> > > +	prop = drm_property_create_range(dev, 0, "VRR_MAX_DENOMINATOR", 0, U32_MAX);
> > > +	if (!prop)
> > > +		return -ENOMEM;
> > > +	dev->mode_config.prop_vrr_max_denominator = prop;
> > > +
> > >  	prop = drm_property_create(dev,
> > >  			DRM_MODE_PROP_BLOB,
> > >  			"DEGAMMA_LUT", 0);
> > > diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> > > index 9d58158af459..df37f4ebb58e 100644
> > > --- a/include/drm/drm_crtc.h
> > > +++ b/include/drm/drm_crtc.h
> > > @@ -67,6 +67,10 @@ struct drm_crtc_vrr_state {
> > >  	u8 vic;
> > >  	u16 cur_vtotal;
> > >  	u16 max_vtotal;
> > > +	u32 vrr_min_n;
> > > +	u32 vrr_min_d;
> > > +	u32 vrr_max_n;
> > > +	u32 vrr_max_d;
> > >  	u16 base_vtotal;
> > >  	bool dynamic;
> > >  };
> > > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> > > index 084517beb924..c8d5286f9267 100644
> > > --- a/include/drm/drm_mode_config.h
> > > +++ b/include/drm/drm_mode_config.h
> > > @@ -702,6 +702,51 @@ struct drm_mode_config {
> > >  	 */
> > >  	struct drm_property *prop_vrr_enabled;
> > >  
> > > +	/**
> > > +	 * @prop_vrr_min_numerator: Default atomic CRTC property to indicate the
> > > +	 * numerator of a numerator/denominator variable refresh rate minimum
> > > +	 * target frame rate.
> > > +	 *
> > > +	 * If not zero, @prop_vrr_min_numerator divided by
> > > +	 * @prop_vrr_min_denominator must result in a frame rate above the
> > > +	 * sink's minimum VRR rate.
> > > +	 */
> > > +	struct drm_property *prop_vrr_min_numerator;
> > > +
> > > +	/**
> > > +	 * @prop_vrr_min_denominator: Default atomic CRTC property to indicate
> > > +	 * the denominator of a numerator/denominator variable refresh rate
> > > +	 * minimum target frame rate.
> > > +	 *
> > > +	 * If @prop_vrr_min_numerator is set, @prop_vrr_min_denominator must not
> > > +	 * be 0, and @prop_vrr_min_numerator divided by @prop_vrr_min_denominator
> > > +	 * must result in a frame rate above the minimum VRR rate.
> > > +	 */
> > > +	struct drm_property *prop_vrr_min_denominator;
> > > +
> > > +	/**
> > > +	 * @prop_vrr_max_numerator: Default atomic CRTC property to indicate the
> > > +	 * numerator of a numerator/denominator variable refresh rate maximum
> > > +	 * target frame rate range.
> > > +	 *
> > > +	 * The fraction expressed by this property divided by its corresponding
> > > +	 * denominator must be equal to or greater than the value of
> > > +	 * @prop_vrr_min_numerator.
> > > +	 */
> > > +	struct drm_property *prop_vrr_max_numerator;
> > > +
> > > +	/**
> > > +	 * @prop_vrr_max_denominator: Default atomic CRTC property to indicate
> > > +	 * the denominator of a numerator/denominator variable refresh rate
> > > +	 * maximum target frame rate range.
> > > +	 *
> > > +	 * If @prop_vrr_max_numerator is set, @prop_vrr_max_denominator must not
> > > +	 * be 0, and @prop_vrr_max_numerator divided by @prop_vrr_max_denominator
> > > +	 * must result in a frame rate equal to or above @prop_vrr_min_numerator
> > > +	 * divided by @prop_vrr_min_denominator.
> > > +	 */
> > > +	struct drm_property *prop_vrr_max_denominator;
> > > +
> > >  	/**
> > >  	 * @dvi_i_subconnector_property: Optional DVI-I property to
> > >  	 * differentiate between analog or digital mode.
> > > 
> > 
> 
> 
> 
> 
>