diff options
| -rw-r--r-- | Documentation/gpu/drm-kms.rst | 7 | ||||
| -rw-r--r-- | drivers/gpu/drm/drm_connector.c | 68 |
2 files changed, 75 insertions, 0 deletions
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 7bd9d824dd7d..ead26bfc30ca 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -1272,6 +1272,74 @@ 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 * @connector: connector to create the vrr_capable property on. |