Re: [DPU PATCH 06/11] drm/msm: Remove msm_commit/kthread, use atomic helper commit

[jsanka-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org]

On 2018-03-01 07:27, Sean Paul wrote:
> On Wed, Feb 28, 2018 at 08:07:00PM -0800, jsanka@codeaurora.org wrote:
>> On 2018-02-28 11:19, Sean Paul wrote:
>> > Moving further towards switching fully to the the atomic helpers, this
>> > patch removes the hand-rolled kthread nonblock commit code and uses
> the
>> > atomic helpers commit_work model.
>> >
>> > There's still a lot of copypasta here, but it's still needed to
>> > facilitate the swap_state and prepare_fence private functions. These
>> > will be sorted out in a follow-on patch.
>> >
>> > Change-Id: I9fcba27824ba63d3fab96cb2bc194bfa6f3475b7
>> > Signed-off-by: Sean Paul <seanpaul@chromium.org>
>> > ---
>> >  drivers/gpu/drm/msm/msm_atomic.c | 199
> ++++++-------------------------
>> >  drivers/gpu/drm/msm/msm_drv.c    |   1 -
>> >  drivers/gpu/drm/msm/msm_drv.h    |   4 -
>> >  3 files changed, 35 insertions(+), 169 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/msm/msm_atomic.c
>> > b/drivers/gpu/drm/msm/msm_atomic.c
>> > index 3a18bd3dc215..7e54eb65d096 100644
>> > --- a/drivers/gpu/drm/msm/msm_atomic.c
>> > +++ b/drivers/gpu/drm/msm/msm_atomic.c
>> > @@ -21,51 +21,6 @@
>> >  #include "msm_gem.h"
>> >  #include "msm_fence.h"
>> >
>> > -struct msm_commit {
>> > -	struct drm_device *dev;
>> > -	struct drm_atomic_state *state;
>> > -	uint32_t crtc_mask;
>> > -	bool nonblock;
>> > -	struct kthread_work commit_work;
>> > -};
>> > -
>> > -/* block until specified crtcs are no longer pending update, and
>> > - * atomically mark them as pending update
>> > - */
>> > -static int start_atomic(struct msm_drm_private *priv, uint32_t
>> > crtc_mask)
>> > -{
>> > -	int ret;
>> > -
>> > -	spin_lock(&priv->pending_crtcs_event.lock);
>> > -	ret = wait_event_interruptible_locked(priv->pending_crtcs_event,
>> > -			!(priv->pending_crtcs & crtc_mask));
>> > -	if (ret == 0) {
>> > -		DBG("start: %08x", crtc_mask);
>> > -		priv->pending_crtcs |= crtc_mask;
>> > -	}
>> > -	spin_unlock(&priv->pending_crtcs_event.lock);
>> > -
>> > -	return ret;
>> > -}
>> > -
>> > -/* clear specified crtcs (no longer pending update)
>> > - */
>> > -static void end_atomic(struct msm_drm_private *priv, uint32_t
>> > crtc_mask)
>> > -{
>> > -	spin_lock(&priv->pending_crtcs_event.lock);
>> > -	DBG("end: %08x", crtc_mask);
>> > -	priv->pending_crtcs &= ~crtc_mask;
>> > -	wake_up_all_locked(&priv->pending_crtcs_event);
>> > -	spin_unlock(&priv->pending_crtcs_event.lock);
>> > -}
>> > -
>> > -static void commit_destroy(struct msm_commit *c)
>> > -{
>> > -	end_atomic(c->dev->dev_private, c->crtc_mask);
>> > -	if (c->nonblock)
>> > -		kfree(c);
>> > -}
>> > -
>> >  static void msm_atomic_wait_for_commit_done(
>> >  		struct drm_device *dev,
>> >  		struct drm_atomic_state *old_state)
>> > @@ -118,6 +73,10 @@ static void msm_atomic_commit_tail(struct
>> > drm_atomic_state *state)
>> >
>> >  	msm_atomic_wait_for_commit_done(dev, state);
>> >
>> > +	drm_atomic_helper_commit_hw_done(state);
>> > +
>> > +	drm_atomic_helper_wait_for_vblanks(dev, state);
>> > +
>> >  	drm_atomic_helper_cleanup_planes(dev, state);
>> >
>> >  	kms->funcs->complete_commit(kms, state);
>> > @@ -126,109 +85,25 @@ static void msm_atomic_commit_tail(struct
>> > drm_atomic_state *state)
>> >  /* The (potentially) asynchronous part of the commit.  At this point
>> >   * nothing can fail short of armageddon.
>> >   */
>> > -static void complete_commit(struct msm_commit *c)
>> > +static void commit_tail(struct drm_atomic_state *state)
>> >  {
>> > -	struct drm_atomic_state *state = c->state;
>> > -	struct drm_device *dev = state->dev;
>> > +	drm_atomic_helper_wait_for_fences(state->dev, state, false);
>> >
>> > -	drm_atomic_helper_wait_for_fences(dev, state, false);
>> > +	drm_atomic_helper_wait_for_dependencies(state);
>> >
>> >  	msm_atomic_commit_tail(state);
>> >
>> > -	drm_atomic_state_put(state);
>> > -}
>> > -
>> > -static void _msm_drm_commit_work_cb(struct kthread_work *work)
>> > -{
>> > -	struct msm_commit *commit =  NULL;
>> > -
>> > -	if (!work) {
>> > -		DRM_ERROR("%s: Invalid commit work data!\n", __func__);
>> > -		return;
>> > -	}
>> > -
>> > -	commit = container_of(work, struct msm_commit, commit_work);
>> > -
>> > -	complete_commit(commit);
>> > -
>> > -	commit_destroy(commit);
>> > -}
>> > -
>> > -static struct msm_commit *commit_init(struct drm_atomic_state *state,
>> > -		bool nonblock)
>> > -{
>> > -	struct msm_commit *c = kzalloc(sizeof(*c), GFP_KERNEL);
>> > +	drm_atomic_helper_commit_cleanup_done(state);
>> >
>> > -	if (!c)
>> > -		return NULL;
>> > -
>> > -	c->dev = state->dev;
>> > -	c->state = state;
>> > -	c->nonblock = nonblock;
>> > -
>> > -	kthread_init_work(&c->commit_work, _msm_drm_commit_work_cb);
>> > -
>> > -	return c;
>> > +	drm_atomic_state_put(state);
>> >  }
>> >
>> > -/* Start display thread function */
>> > -static void msm_atomic_commit_dispatch(struct drm_device *dev,
>> > -		struct drm_atomic_state *state, struct msm_commit *commit)
>> > +static void commit_work(struct work_struct *work)
>> >  {
>> > -	struct msm_drm_private *priv = dev->dev_private;
>> > -	struct drm_crtc *crtc = NULL;
>> > -	struct drm_crtc_state *new_crtc_state = NULL;
>> > -	int ret = -EINVAL, i = 0, j = 0;
>> > -	bool nonblock;
>> > -
>> > -	/* cache since work will kfree commit in non-blocking case */
>> > -	nonblock = commit->nonblock;
>> > -
>> > -	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
>> > -		for (j = 0; j < priv->num_crtcs; j++) {
>> > -			if (priv->disp_thread[j].crtc_id ==
>> > -						crtc->base.id) {
>> > -				if (priv->disp_thread[j].thread) {
>> > -					kthread_queue_work(
>> > -
>> > &priv->disp_thread[j].worker,
>> > -
>> > &commit->commit_work);
>> Are there any known proposals floating around to support ASYNC commits
> for
>> concurrent displays rendering at different FPS? The above kthread 
>> model
> is
>> introduced when we faced some performance road blockers when a display
> has
>> to wait for an ongoing display commit to complete.
> 
> I think people have discussed it, I'm not sure if there are any patches
> floating
> around. On the surface, it seems easy to just push the commit_work into
> the crtc
> commit and have one work item per crtc. However I think the problem is
> that there
> could be resources switching between crtcs for a given commit, or from 
> one
> commit
> to the next, and synchronizing that becomes a Hard Problem.
> 
> Perhaps I'm misunderstanding, but the start/end atomic functions 
> serialize
> the
> incoming commits, right? So the only benefit the kthread provides is to
> mitigate
> any blocking calls made on one crtc from blocking a second crtc in the
> same
> commit?
> 
> Sean
I am not sure what level of resource (I assume hw blocks) switching we 
can expect between
two active CRTC's on successive commits. With virtualization in play, 
the resources allocated to
CRTC / encoder / Connector will remain attached to the components as 
long as the display is active.
Planes (HW pipes) are one such entity which can move between the CRTC's 
frequently. Even
with them planes, the hw assignment should remain valid until the plane 
is detached from
a CRTC before attaching to the next one.

"Start atomic" synchronizes the commit cycle for all the CRTC's by 
waiting for commit complete
of all the previous frames. But per crtc kthreads allows the current 
frame commits to happen
independently. For android, we needed this model as each commit thread 
need to wait for input
plane fences before programming the hardware.

Jeykumar S.
> 
>> > -					/* only return zero if work is
>> > -					 * queued successfully.
>> > -					 */
>> > -					ret = 0;
>> > -				} else {
>> > -					DRM_ERROR(" Error for crtc_id:
>> > %d\n",
>> > -
>> > priv->disp_thread[j].crtc_id);
>> > -				}
>> > -				break;
>> > -			}
>> > -		}
>> > -		/*
>> > -		 * TODO: handle cases where there will be more than
>> > -		 * one crtc per commit cycle. Remove this check then.
>> > -		 * Current assumption is there will be only one crtc
>> > -		 * per commit cycle.
>> > -		 */
>> > -		if (j < priv->num_crtcs)
>> > -			break;
>> > -	}
>> > -
>> > -	if (ret) {
>> > -		/**
>> > -		 * this is not expected to happen, but at this point the
>> > state
>> > -		 * has been swapped, but we couldn't dispatch to a crtc
>> > thread.
>> > -		 * fallback now to a synchronous complete_commit to try
>> > and
>> > -		 * ensure that SW and HW state don't get out of sync.
>> > -		 */
>> > -		DRM_ERROR("failed to dispatch commit to any CRTC\n");
>> > -		complete_commit(commit);
>> > -	} else if (!nonblock) {
>> > -		kthread_flush_work(&commit->commit_work);
>> > -	}
>> > -
>> > -	/* free nonblocking commits in this context, after processing */
>> > -	if (!nonblock)
>> > -		kfree(commit);
>> > +	struct drm_atomic_state *state = container_of(work,
>> > +						      struct
>> > drm_atomic_state,
>> > +						      commit_work);
>> > +	commit_tail(state);
>> >  }
>> >
>> >  /**
>> > @@ -247,17 +122,12 @@ int msm_atomic_commit(struct drm_device *dev,
>> >  		struct drm_atomic_state *state, bool nonblock)
>> >  {
>> >  	struct msm_drm_private *priv = dev->dev_private;
>> > -	struct msm_commit *c;
>> >  	struct drm_crtc *crtc;
>> >  	struct drm_crtc_state *crtc_state;
>> >  	struct drm_plane *plane;
>> >  	struct drm_plane_state *old_plane_state, *new_plane_state;
>> >  	int i, ret;
>> >
>> > -	ret = drm_atomic_helper_prepare_planes(dev, state);
>> > -	if (ret)
>> > -		return ret;
>> > -
>> >  	/*
>> >  	 * Note that plane->atomic_async_check() should fail if we need
>> >  	 * to re-assign hwpipe or anything that touches global atomic
>> > @@ -265,32 +135,30 @@ int msm_atomic_commit(struct drm_device *dev,
>> >  	 * cases.
>> >  	 */
>> >  	if (state->async_update) {
>> > +		ret = drm_atomic_helper_prepare_planes(dev, state);
>> > +		if (ret)
>> > +			return ret;
>> > +
>> >  		drm_atomic_helper_async_commit(dev, state);
>> >  		drm_atomic_helper_cleanup_planes(dev, state);
>> >  		return 0;
>> >  	}
>> >
>> > -	c = commit_init(state, nonblock);
>> > -	if (!c) {
>> > -		ret = -ENOMEM;
>> > -		goto error;
>> > -	}
>> > +	ret = drm_atomic_helper_setup_commit(state, nonblock);
>> > +	if (ret)
>> > +		return ret;
>> >
>> > -	/*
>> > -	 * Figure out what crtcs we have:
>> > -	 */
>> > -	for_each_new_crtc_in_state(state, crtc, crtc_state, i)
>> > -		c->crtc_mask |= drm_crtc_mask(crtc);
>> > +	INIT_WORK(&state->commit_work, commit_work);
>> >
>> > -	/*
>> > -	 * Wait for pending updates on any of the same crtc's and then
>> > -	 * mark our set of crtc's as busy:
>> > -	 */
>> > -	ret = start_atomic(dev->dev_private, c->crtc_mask);
>> > +	ret = drm_atomic_helper_prepare_planes(dev, state);
>> >  	if (ret)
>> > -		goto err_free;
>> > +		return ret;
>> >
>> > -	BUG_ON(drm_atomic_helper_swap_state(state, false) < 0);
>> > +	if (!nonblock) {
>> > +		ret = drm_atomic_helper_wait_for_fences(dev, state, true);
>> > +		if (ret)
>> > +			goto error;
>> > +	}
>> >
>> >  	/*
>> >  	 * This is the point of no return - everything below never fails
>> > except
>> > @@ -299,6 +167,8 @@ int msm_atomic_commit(struct drm_device *dev,
>> >  	 *
>> >  	 * swap driver private state while still holding state_lock
>> >  	 */
>> > +	BUG_ON(drm_atomic_helper_swap_state(state, false) < 0);
>> > +
>> >  	if (to_kms_state(state)->state)
>> >  		priv->kms->funcs->swap_state(priv->kms, state);
>> >
>> > @@ -329,12 +199,13 @@ int msm_atomic_commit(struct drm_device *dev,
>> >  	 */
>> >
>> >  	drm_atomic_state_get(state);
>> > -	msm_atomic_commit_dispatch(dev, state, c);
>> > +	if (nonblock)
>> > +		queue_work(system_unbound_wq, &state->commit_work);
>> > +	else
>> > +		commit_tail(state);
>> >
>> >  	return 0;
>> >
>> > -err_free:
>> > -	kfree(c);
>> >  error:
>> >  	drm_atomic_helper_cleanup_planes(dev, state);
>> >  	return ret;
>> > diff --git a/drivers/gpu/drm/msm/msm_drv.c
>> > b/drivers/gpu/drm/msm/msm_drv.c
>> > index eda4a2340f93..b354424cccb5 100644
>> > --- a/drivers/gpu/drm/msm/msm_drv.c
>> > +++ b/drivers/gpu/drm/msm/msm_drv.c
>> > @@ -549,7 +549,6 @@ static int msm_drm_init(struct device *dev, struct
>> > drm_driver *drv)
>> >  		goto mdss_init_fail;
>> >
>> >  	priv->wq = alloc_ordered_workqueue("msm_drm", 0);
>> > -	init_waitqueue_head(&priv->pending_crtcs_event);
>> >
>> >  	INIT_LIST_HEAD(&priv->client_event_list);
>> >  	INIT_LIST_HEAD(&priv->inactive_list);
>> > diff --git a/drivers/gpu/drm/msm/msm_drv.h
>> > b/drivers/gpu/drm/msm/msm_drv.h
>> > index cf96a85f4b55..292496b682e8 100644
>> > --- a/drivers/gpu/drm/msm/msm_drv.h
>> > +++ b/drivers/gpu/drm/msm/msm_drv.h
>> > @@ -536,10 +536,6 @@ struct msm_drm_private {
>> >
>> >  	struct workqueue_struct *wq;
>> >
>> > -	/* crtcs pending async atomic updates: */
>> > -	uint32_t pending_crtcs;
>> > -	wait_queue_head_t pending_crtcs_event;
>> > -
>> >  	unsigned int num_planes;
>> >  	struct drm_plane *planes[MAX_PLANES];
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