On Thu, Jan 23, 2020 at 10:21:09AM +0100, Thomas Zimmermann wrote:
> At the end of a commit, atomic helpers can generate a 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
> VBLANK generation.
>
> The new interface drm_dev_has_vblank() returns true if vblanking has
> been initialized for a device, or false otherwise. This function will
> be useful when initializing no_vblank in the CRTC state.
>
> Atomic modesetting helper set the initial value of no_vblank 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 VBLANK events with any
> driver that did not initialize vblanking.
>
> v4:
> * replace drm_crtc_has_vblank() with drm_dev_has_vblank()
> * add drm_dev_crtc_has_vblank() in this patch
drm_dev_has_vblank I guess?
> * 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>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 10 +++++++++-
> drivers/gpu/drm/drm_vblank.c | 28 ++++++++++++++++++++++++++++
> include/drm/drm_crtc.h | 27 ++++++++++++++++++++-------
> include/drm/drm_simple_kms_helper.h | 7 +++++--
> include/drm/drm_vblank.h | 1 +
> 5 files changed, 63 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 4511c2e07bb9..d7b73cd89b79 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -583,6 +583,7 @@ mode_valid(struct drm_atomic_state *state)
> * &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:
> @@ -649,6 +650,11 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
>
> 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);
> @@ -2215,7 +2221,9 @@ EXPORT_SYMBOL(drm_atomic_helper_wait_for_dependencies);
> * 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 1659b13b178c..433dec6230b1 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 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
> @@ -501,6 +507,28 @@ 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 5e9b15a0e8c5..5363e31c9abe 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -174,12 +174,22 @@ 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 sendout a fake VBLANK event during display
s/sendout/ send out/
> + * updates.
maby add "... updates, after all hardware changes have been committed.
This is implemented in drm_atomic_helper_fake_vblank()."
That at least reflects the default behaviour.
> + *
> + * 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() wit the number of CRTCs). For CRTCs
s/wit/with/
> + * without initialized vblanking, the field is initialized to true and
"initialized to true" is a bit a stretch, since this is done in the
helpers. Maybe instead "... this field is set to true in
drm_atomic_helper_check_modeset() and ..."
> + * a VBLANK event will be send out on each update of the display
> + * pipeline.
Maybe also reiterate that this is done through
drm_atomic_helper_fake_vblank() again? Imo for stuff done by helpers it's
important to highligh where that's done, since it's all opt-in (even if
most drivers will opt-in automatically).
> + *
> + * Another usage 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.
> *
> * __drm_atomic_helper_crtc_duplicate_state() will not reset the value
> * from the current state, the CRTC driver is then responsible for
> @@ -335,7 +345,10 @@ 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 the event at an appropriate time. 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 15afee9cf049..e253ba7bea9d 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 c16c44052b3d..94275e93fd27 100644
> --- a/include/drm/drm_vblank.h
> +++ b/include/drm/drm_vblank.h
> @@ -206,6 +206,7 @@ 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);
With the doc nits addressed:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> --
> 2.24.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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