robert.foss at collabora.com writes:
> From: Robert Foss <robert.foss at collabora.com>
>
> As per the docs, atomic_commit should return -EBUSY "if an asycnhronous
> update is requested and there is an earlier update pending".
Note: docs cited here are drm_crtc.h, and the whole quote is:
* - -EBUSY, if an asynchronous updated is requested and there is
* an earlier updated pending. Drivers are allowed to support a queue
* of outstanding updates, but currently no driver supports that.
* Note that drivers must wait for preceding updates to complete if a
* synchronous update is requested, they are not allowed to fail the
* commit in that case.
> Signed-off-by: Robert Foss <robert.foss at collabora.com>
> ---
> drivers/gpu/drm/vc4/vc4_crtc.c | 6 ++++++
> drivers/gpu/drm/vc4/vc4_drv.h | 1 +
> drivers/gpu/drm/vc4/vc4_kms.c | 20 ++++++++++++++++++--
> 3 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
> index 355ee4b..43193a3 100644
> --- a/drivers/gpu/drm/vc4/vc4_crtc.c
> +++ b/drivers/gpu/drm/vc4/vc4_crtc.c
> @@ -802,3 +802,9 @@ struct platform_driver vc4_crtc_driver = {
> .of_match_table = vc4_crtc_dt_match,
> },
> };
> +
> +bool vc4_crtc_has_pending_event(struct drm_crtc *crtc)
> +{
> + assert_spin_locked(&crtc->dev->event_lock);
> + return to_vc4_crtc(crtc)->event;
> +}
> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
> index fa2ad15..54c1fb5 100644
> --- a/drivers/gpu/drm/vc4/vc4_drv.h
> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
> @@ -414,6 +414,7 @@ extern struct platform_driver vc4_crtc_driver;
> int vc4_enable_vblank(struct drm_device *dev, unsigned int crtc_id);
> void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id);
> int vc4_crtc_debugfs_regs(struct seq_file *m, void *arg);
> +bool vc4_crtc_has_pending_event(struct drm_crtc *crtc);
>
> /* vc4_debugfs.c */
> int vc4_debugfs_init(struct drm_minor *minor);
> diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
> index 4718ae5..dc157a1e 100644
> --- a/drivers/gpu/drm/vc4/vc4_kms.c
> +++ b/drivers/gpu/drm/vc4/vc4_kms.c
> @@ -107,10 +107,26 @@ static int vc4_atomic_commit(struct drm_device *dev,
> bool async)
> {
> struct vc4_dev *vc4 = to_vc4_dev(dev);
> - int ret;
> - int i;
> uint64_t wait_seqno = 0;
> struct vc4_commit *c;
> + struct drm_crtc_state *crtc_state;
> + struct drm_crtc *crtc;
> + unsigned long flags;
> + int i, ret;
> +
> + if (async) {
> + for_each_crtc_in_state(state, crtc, crtc_state, i) {
> +
> + spin_lock_irqsave(&dev->event_lock, flags);
> +
> + if (crtc->state->event ||
> + vc4_crtc_has_pending_event(crtc)) {
> + spin_unlock_irqrestore(&dev->event_lock, flags);
> + return -EBUSY;
> + }
> + spin_unlock_irqrestore(&dev->event_lock, flags);
> + }
> + }
By my reading, the point of returning -EBUSY here is just to avoid
blocking when the compositor asked for nonblocking. You're checking
that each CRTC involved in the commit doesn't have a queued pageflip
event, except that then we immediately proceed to:
/* Make sure that any outstanding modesets have finished. */
ret = down_interruptible(&vc4->async_modeset);
if (ret) {
kfree(c);
return ret;
}
so this per-CRTC check doesn't prevent blocking if the set of CRTCs for
this commit was disjoint from the last one, right? To implement the
minimal behavior, I think we'd want to just down_trylock instead in the
async case, I think. And to implement the disjoint CRTC thing you were
trying for, I think we'd need to track a mask kind of like msm's
pending_crtcs.
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