From: Thomas Zimmermann <tzimmermann@xxxxxxx> At the end of a commit, atomic helpers can generate a fake VBLANK event automatically. Originally implemented for writeback connectors, the functionality can be used by any driver and/or hardware without proper VBLANK interrupt. The patch updates the documentation to make this behaviour official: settings struct drm_crtc_state.no_vblank to true enables automatic generation of fake VBLANK events. The new interface drm_dev_has_vblank() returns true if vblanking has been initialized for a device, or false otherwise. Atomic helpers use this function when initializing no_vblank in the CRTC state in drm_atomic_helper_check_modeset(). If vblanking has been initialized for a device, no_blank is disabled. Otherwise it's enabled. Hence, atomic helpers will automatically send out fake VBLANK events with any driver that did not initialize vblanking. v5: * more precise documentation and commit message v4: * replace drm_crtc_has_vblank() with drm_dev_has_vblank() * add drm_dev_has_vblank() in this patch * move driver changes into separate patches v3: * squash all related changes patches into this patch Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx> Acked-by: Gerd Hoffmann <kraxel@xxxxxxxxxx> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20200129120531.6891-2-tzimmermann@xxxxxxx (cherry picked from commit 7beb691f1e6f349c9df3384a85e7a53c5601aaaf) Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx> --- drivers/gpu/drm/drm_atomic_helper.c | 10 +++++++++- drivers/gpu/drm/drm_vblank.c | 28 ++++++++++++++++++++++++++++ include/drm/drm_crtc.h | 34 +++++++++++++++++++++++++++------- include/drm/drm_simple_kms_helper.h | 7 +++++-- include/drm/drm_vblank.h | 1 + 5 files changed, 70 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 5e906ea..9a5eb76 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -588,6 +588,7 @@ static enum drm_mode_status mode_valid_path(struct drm_connector *connector, * &drm_crtc_state.connectors_changed is set when a connector is added or * removed from the crtc. &drm_crtc_state.active_changed is set when * &drm_crtc_state.active changes, which is used for DPMS. + * &drm_crtc_state.no_vblank is set from the result of drm_dev_has_vblank(). * See also: drm_atomic_crtc_needs_modeset() * * IMPORTANT: @@ -654,6 +655,11 @@ static enum drm_mode_status mode_valid_path(struct drm_connector *connector, return -EINVAL; } + + if (drm_dev_has_vblank(dev)) + new_crtc_state->no_vblank = false; + else + new_crtc_state->no_vblank = true; } ret = handle_conflicting_encoders(state, false); @@ -2202,7 +2208,9 @@ void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *old_state) * when a job is queued, and any change to the pipeline that does not touch the * connector is leading to timeouts when calling * drm_atomic_helper_wait_for_vblanks() or - * drm_atomic_helper_wait_for_flip_done(). + * drm_atomic_helper_wait_for_flip_done(). In addition to writeback + * connectors, this function can also fake VBLANK events for CRTCs without + * VBLANK interrupt. * * This is part of the atomic helper support for nonblocking commits, see * drm_atomic_helper_setup_commit() for an overview. diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index 552ec82..c98ed814 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -69,6 +69,12 @@ * &drm_driver.max_vblank_count. In that case the vblank core only disables the * vblanks after a timer has expired, which can be configured through the * ``vblankoffdelay`` module parameter. + * + * Drivers for hardware without support for vertical-blanking interrupts + * must not call drm_vblank_init(). For such drivers, atomic helpers will + * automatically generate fake vblank events as part of the display update. + * This functionality also can be controlled by the driver by enabling and + * disabling struct drm_crtc_state.no_vblank. */ /* Retry timestamp calculation up to 3 times to satisfy @@ -489,6 +495,28 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs) EXPORT_SYMBOL(drm_vblank_init); /** + * drm_dev_has_vblank - test if vblanking has been initialized for + * a device + * @dev: the device + * + * Drivers may call this function to test if vblank support is + * initialized for a device. For most hardware this means that vblanking + * can also be enabled. + * + * Atomic helpers use this function to initialize + * &drm_crtc_state.no_vblank. See also drm_atomic_helper_check_modeset(). + * + * Returns: + * True if vblanking has been initialized for the given device, false + * otherwise. + */ +bool drm_dev_has_vblank(const struct drm_device *dev) +{ + return dev->num_crtcs != 0; +} +EXPORT_SYMBOL(drm_dev_has_vblank); + +/** * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC * @crtc: which CRTC's vblank waitqueue to retrieve * diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 408b6f4..ebcce95 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 diff --git a/include/drm/drm_simple_kms_helper.h b/include/drm/drm_simple_kms_helper.h index 4d89cd0..df615eb 100644 --- a/include/drm/drm_simple_kms_helper.h +++ b/include/drm/drm_simple_kms_helper.h @@ -100,8 +100,11 @@ struct drm_simple_display_pipe_funcs { * This is the function drivers should submit the * &drm_pending_vblank_event from. Using either * drm_crtc_arm_vblank_event(), when the driver supports vblank - * interrupt handling, or drm_crtc_send_vblank_event() directly in case - * the hardware lacks vblank support entirely. + * interrupt handling, or drm_crtc_send_vblank_event() for more + * complex case. In case the hardware lacks vblank support entirely, + * drivers can set &struct drm_crtc_state.no_vblank in + * &struct drm_simple_display_pipe_funcs.check and let DRM's + * atomic helper fake a vblank event. */ void (*update)(struct drm_simple_display_pipe *pipe, struct drm_plane_state *old_plane_state); diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h index 9fe4ba8..2559fb9 100644 --- a/include/drm/drm_vblank.h +++ b/include/drm/drm_vblank.h @@ -195,6 +195,7 @@ struct drm_vblank_crtc { }; int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs); +bool drm_dev_has_vblank(const struct drm_device *dev); u64 drm_crtc_vblank_count(struct drm_crtc *crtc); u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc, ktime_t *vblanktime); -- 1.8.3.1
