[PATCH v7 3/5] drm: Document variable refresh properties

[Wentland, Harry]

On 2018-11-12 12:05 p.m., Kazlauskas, Nicholas wrote:
> On 11/12/18 11:12 AM, Wentland, Harry wrote:
>> On 2018-11-08 9:43 a.m., Nicholas Kazlauskas wrote:
>>> These include the drm_connector 'vrr_capable' and the drm_crtc
>>> 'vrr_enabled' properties.
>>>
>>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>>> Cc: Harry Wentland <harry.wentland at amd.com>
>>> Cc: Manasi Navare <manasi.d.navare at intel.com>
>>> Cc: Pekka Paalanen <ppaalanen at gmail.com>
>>> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
>>> Cc: Michel Dänzer <michel at daenzer.net>
>>
>> Looks good. Whole series is
>> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
>>
>> How are we with the userspace patches? We should probably hold off pushing the kernel patches until the userspace work is all reviewed.
>>
>> Harry
> 
> Thanks for the review.
> 
> The xf86-video-amdgpu patches have been reviewed and the mesa patches 
> have been partially reviewed.
> 

Alex, Michel,

how do we merge changes like this that provide a kernel API that goes together with userspace changes?

I imagine we'd want to get the kernel changes in first, and then merge the xf86-video-amdgpu and mesa changes. Please correct me if I'm wrong. Any objections to getting this merged via the usual amd-stg?

Thanks,
Harry


> Nicholas Kazlauskas
> 
>>
>>> ---
>>>   Documentation/gpu/drm-kms.rst   |  7 ++++
>>>   drivers/gpu/drm/drm_connector.c | 68 +++++++++++++++++++++++++++++++++
>>>   2 files changed, 75 insertions(+)
>>>
>>> diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
>>> index 4b1501b4835b..8da2a178cf85 100644
>>> --- a/Documentation/gpu/drm-kms.rst
>>> +++ b/Documentation/gpu/drm-kms.rst
>>> @@ -575,6 +575,13 @@ Explicit Fencing Properties
>>>   .. kernel-doc:: drivers/gpu/drm/drm_atomic_uapi.c
>>>      :doc: explicit fencing properties
>>>   
>>> +
>>> +Variable Refresh Properties
>>> +---------------------------
>>> +
>>> +.. kernel-doc:: drivers/gpu/drm/drm_connector.c
>>> +   :doc: Variable refresh properties
>>> +
>>>   Existing KMS Properties
>>>   -----------------------
>>>   
>>> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
>>> index 49290060ab7b..0e4287461997 100644
>>> --- a/drivers/gpu/drm/drm_connector.c
>>> +++ b/drivers/gpu/drm/drm_connector.c
>>> @@ -1255,6 +1255,74 @@ int drm_mode_create_scaling_mode_property(struct drm_device *dev)
>>>   }
>>>   EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
>>>   
>>> +/**
>>> + * DOC: Variable refresh properties
>>> + *
>>> + * Variable refresh rate capable displays can dynamically adjust their
>>> + * refresh rate by extending the duration of their vertical front porch
>>> + * until page flip or timeout occurs. This can reduce or remove stuttering
>>> + * and latency in scenarios where the page flip does not align with the
>>> + * vblank interval.
>>> + *
>>> + * An example scenario would be an application flipping at a constant rate
>>> + * of 48Hz on a 60Hz display. The page flip will frequently miss the vblank
>>> + * interval and the same contents will be displayed twice. This can be
>>> + * observed as stuttering for content with motion.
>>> + *
>>> + * If variable refresh rate was active on a display that supported a
>>> + * variable refresh range from 35Hz to 60Hz no stuttering would be observable
>>> + * for the example scenario. The minimum supported variable refresh rate of
>>> + * 35Hz is below the page flip frequency and the vertical front porch can
>>> + * be extended until the page flip occurs. The vblank interval will be
>>> + * directly aligned to the page flip rate.
>>> + *
>>> + * Not all userspace content is suitable for use with variable refresh rate.
>>> + * Large and frequent changes in vertical front porch duration may worsen
>>> + * perceived stuttering for input sensitive applications.
>>> + *
>>> + * Panel brightness will also vary with vertical front porch duration. Some
>>> + * panels may have noticeable differences in brightness between the minimum
>>> + * vertical front porch duration and the maximum vertical front porch duration.
>>> + * Large and frequent changes in vertical front porch duration may produce
>>> + * observable flickering for such panels.
>>> + *
>>> + * Userspace control for variable refresh rate is supported via properties
>>> + * on the &drm_connector and &drm_crtc objects.
>>> + *
>>> + * "vrr_capable":
>>> + *	Optional &drm_connector boolean property that drivers should attach
>>> + *	with drm_connector_attach_vrr_capable_property() on connectors that
>>> + *	could support variable refresh rates. Drivers should update the
>>> + *	property value by calling drm_connector_set_vrr_capable_property().
>>> + *
>>> + *	Absence of the property should indicate absence of support.
>>> + *
>>> + * "vrr_enabled":
>>> + *	Default &drm_crtc boolean property that notifies the driver that the
>>> + *	content on the CRTC is suitable for variable refresh rate presentation.
>>> + *	The driver will take this property as a hint to enable variable
>>> + *	refresh rate support if the receiver supports it, ie. if the
>>> + *	"vrr_capable" property is true on the &drm_connector object. The
>>> + *	vertical front porch duration will be extended until page-flip or
>>> + *	timeout when enabled.
>>> + *
>>> + *	The minimum vertical front porch duration is defined as the vertical
>>> + *	front porch duration for the current mode.
>>> + *
>>> + *	The maximum vertical front porch duration is greater than or equal to
>>> + *	the minimum vertical front porch duration. The duration is derived
>>> + *	from the minimum supported variable refresh rate for the connector.
>>> + *
>>> + *	The driver may place further restrictions within these minimum
>>> + *	and maximum bounds.
>>> + *
>>> + *	The semantics for the vertical blank timestamp differ when
>>> + *	variable refresh rate is active. The vertical blank timestamp
>>> + *	is defined to be an estimate using the current mode's fixed
>>> + *	refresh rate timings. The semantics for the page-flip event
>>> + *	timestamp remain the same.
>>> + */
>>> +
>>>   /**
>>>    * drm_connector_attach_vrr_capable_property - creates the
>>>    * vrr_capable property
>>>
>