diff options
Diffstat (limited to 'include/drm/drm_crtc.h')
| -rw-r--r-- | include/drm/drm_crtc.h | 34 |
1 files changed, 27 insertions, 7 deletions
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 408b6f4e63c0..ebcce95f9da6 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -175,12 +175,25 @@ struct drm_crtc_state { * @no_vblank: * * Reflects the ability of a CRTC to send VBLANK events. This state - * usually depends on the pipeline configuration, and the main usuage - * is CRTCs feeding a writeback connector operating in oneshot mode. - * In this case the VBLANK event is only generated when a job is queued - * to the writeback connector, and we want the core to fake VBLANK - * events when this part of the pipeline hasn't changed but others had - * or when the CRTC and connectors are being disabled. + * usually depends on the pipeline configuration. If set to true, DRM + * atomic helpers will send out a fake VBLANK event during display + * updates after all hardware changes have been committed. This is + * implemented in drm_atomic_helper_fake_vblank(). + * + * One usage is for drivers and/or hardware without support for VBLANK + * interrupts. Such drivers typically do not initialize vblanking + * (i.e., call drm_vblank_init() with the number of CRTCs). For CRTCs + * without initialized vblanking, this field is set to true in + * drm_atomic_helper_check_modeset(), and a fake VBLANK event will be + * send out on each update of the display pipeline by + * drm_atomic_helper_fake_vblank(). + * + * Another usage is CRTCs feeding a writeback connector operating in + * oneshot mode. In this case the fake VBLANK event is only generated + * when a job is queued to the writeback connector, and we want the + * core to fake VBLANK events when this part of the pipeline hasn't + * changed but others had or when the CRTC and connectors are being + * disabled. * * __drm_atomic_helper_crtc_duplicate_state() will not reset the value * from the current state, the CRTC driver is then responsible for @@ -336,7 +349,14 @@ struct drm_crtc_state { * - Events for disabled CRTCs are not allowed, and drivers can ignore * that case. * - * This can be handled by the drm_crtc_send_vblank_event() function, + * For very simple hardware without VBLANK interrupt, enabling + * &struct drm_crtc_state.no_vblank makes DRM's atomic commit helpers + * send a fake VBLANK event at the end of the display update after all + * hardware changes have been applied. See + * drm_atomic_helper_fake_vblank(). + * + * For more complex hardware this + * can be handled by the drm_crtc_send_vblank_event() function, * which the driver should call on the provided event upon completion of * the atomic commit. Note that if the driver supports vblank signalling * and timestamping the vblank counters and timestamps must agree with |