[PATCH v2 4/8] drm/crtc: Add a generic infrastructure to fake VBLANK events
Daniel Vetter
daniel at ffwll.ch
Mon Jul 2 08:02:52 UTC 2018
On Fri, Jun 29, 2018 at 01:17:17PM +0200, Boris Brezillon wrote:
> In some cases CRTCs are active but are not able to generating events, at
> least not at every frame at it's expected to.
> This is typically the case when the CRTC is feeding a writeback connector
> that has no job queued. In this situation the CRTC is usually stopped
> until a new job is queued, and this can lead to timeouts when part of
> the pipeline is updated but no new jobs are queued to the active
> writeback connector.
>
> In order to solve that, we add a ->no_vblank flag to drm_crtc_state
> and ask the CRTC drivers to set it to true when they know they're not
> able to generate VBLANK events. The core drm_atomic_helper_fake_vblank()
> helper can then be used to fake VBLANKs at commit time.
>
> Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>
> ---
> drivers/gpu/drm/drm_atomic_helper.c | 40 +++++++++++++++++++++++++++++++++++++
> include/drm/drm_atomic_helper.h | 1 +
> include/drm/drm_crtc.h | 15 ++++++++++++++
> 3 files changed, 56 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 69063bcf2334..ca586993c2a2 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -2051,6 +2051,46 @@ void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *old_state)
> }
> EXPORT_SYMBOL(drm_atomic_helper_wait_for_dependencies);
>
> +/**
> + * drm_atomic_helper_fake_vblank - fake VBLANK events if needed
> + * @old_state: atomic state object with old state structures
> + *
> + * This function walks all CRTCs and fake VBLANK events on those with
> + * &drm_crtc_state.no_vblank set to true and &drm_crtc_state.event != NULL.
> + * The primary use of this function is writeback connectors working in oneshot
> + * mode and faking VBLANK events. In this case they only fake the VBLANK event
> + * 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().
> + *
> + * This is part of the atomic helper support for nonblocking commits, see
> + * drm_atomic_helper_setup_commit() for an overview.
> + */
> +void drm_atomic_helper_fake_vblank(struct drm_atomic_state *old_state)
> +{
> + struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> + struct drm_crtc *crtc;
> + int i;
> +
> + for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state,
> + new_crtc_state, i) {
> + unsigned long flags;
> +
> + if (!new_crtc_state->no_vblank && !old_crtc_state->no_vblank)
Uh, this essentially makes it impossible to reset no_vblank. For control
flow state bits we only check the new state for it (see e.g. the various
*_changed or plane_bits or whatever).
> + continue;
> +
> + spin_lock_irqsave(&old_state->dev->event_lock, flags);
> + if (new_crtc_state->event) {
> + drm_crtc_send_vblank_event(crtc,
> + new_crtc_state->event);
> + new_crtc_state->event = NULL;
> + }
> + spin_unlock_irqrestore(&old_state->dev->event_lock, flags);
> + }
> +}
> +EXPORT_SYMBOL(drm_atomic_helper_fake_vblank);
> +
> /**
> * drm_atomic_helper_commit_hw_done - setup possible nonblocking commit
> * @old_state: atomic state object with old state structures
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 26aaba58d6ce..99e2a5297c69 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -100,6 +100,7 @@ int __must_check drm_atomic_helper_swap_state(struct drm_atomic_state *state,
> int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
> bool nonblock);
> void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *state);
> +void drm_atomic_helper_fake_vblank(struct drm_atomic_state *state);
> void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *state);
> void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *state);
>
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index 23eddbccab10..7435dc66c08a 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -87,6 +87,20 @@ struct drm_plane_helper_funcs;
> * @zpos_changed: zpos values of planes on this crtc have been updated
> * @color_mgmt_changed: color management properties have changed (degamma or
> * gamma LUT or CSC matrix)
> + * @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 disabled.
s/are disabled/are getting disabled/
You'll never get a request for an event when it's already off.
> + * __drm_atomic_helper_crtc_duplicate_state() will the value from the
> + * current state, the CRTC driver is then responsible for updating this
> + * field when needed.
Not parsing the above ... probably missing a "... will not reset ..."
> + * Note that, even when no_blank is set to true, the CRTC driver can still
> + * steal the &drm_crtc_state.event object and send the event on its own.
> + * That's usually what happens when a job is queued to the writeback
> + * connector.
The last sentence is confusing imo. Just drop it?
Please use the inline comment style for struct members, and then also
polish the formatting a bit (e.g. paragraph breaks, which are only
possible with the inline style).
With the nits addressed:
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> * @plane_mask: bitmask of (1 << drm_plane_index(plane)) of attached planes
> * @connector_mask: bitmask of (1 << drm_connector_index(connector)) of attached connectors
> * @encoder_mask: bitmask of (1 << drm_encoder_index(encoder)) of attached encoders
> @@ -118,6 +132,7 @@ struct drm_crtc_state {
> bool connectors_changed : 1;
> bool zpos_changed : 1;
> bool color_mgmt_changed : 1;
> + bool no_vblank : 1;
>
> /* attached planes bitmask:
> * WARNING: transitional helpers do not maintain plane_mask so
> --
> 2.14.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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