Re: [PATCH v5 4/4] drm/fence: add out-fences support

[Gustavo Padovan <gustavo@padovan.org>]

Hi Brian,

2016-10-20 Brian Starkey <brian.starkey@arm.com>:

> Hi Gustavo,
> 
> I notice your branch has the sync_file refcount change in, but this
> doesn't seem to take account for that. Will you be dropping that
> change to match the semantics of fence_array?

I will drop the fence_get() in the out-fence patch because we already
hold the ref when we create the fence. The sync_file refcount patch will
remain.

> 
> Couple more comments below.
> 
> On Thu, Oct 20, 2016 at 12:50:05PM -0200, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > 
> > Support DRM out-fences by creating a sync_file with a fence for each CRTC
> > that sets the OUT_FENCE_PTR property.
> > 
> > We use the out_fence pointer received in the OUT_FENCE_PTR prop to send
> > the sync_file fd back to userspace.
> > 
> > The sync_file and fd are allocated/created before commit, but the
> > fd_install operation only happens after we know that commit succeed.
> > 
> > In case of error userspace should receive a fd number of -1.
> > 
> > v2: Comment by Rob Clark:
> > 	- Squash commit that adds DRM_MODE_ATOMIC_OUT_FENCE flag here.
> > 
> >    Comment by Daniel Vetter:
> > 	- Add clean up code for out_fences
> > 
> > v3: Comments by Daniel Vetter:
> > 	- create DRM_MODE_ATOMIC_EVENT_MASK
> > 	- userspace should fill out_fences_ptr with the crtc_ids for which
> > 	it wants fences back.
> > 
> > v4: Create OUT_FENCE_PTR properties and remove old approach.
> > 
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > ---
> > drivers/gpu/drm/drm_atomic.c | 116 ++++++++++++++++++++++++++++++++++---------
> > drivers/gpu/drm/drm_crtc.c   |   8 +++
> > include/drm/drm_crtc.h       |  19 +++++++
> > 3 files changed, 119 insertions(+), 24 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index b3284b2..07775fc 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -490,6 +490,8 @@ int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
> > 					&replaced);
> > 		state->color_mgmt_changed |= replaced;
> > 		return ret;
> > +	} else if (property == config->prop_out_fence_ptr) {
> > +		state->out_fence_ptr = u64_to_user_ptr(val);
> > 	} else if (crtc->funcs->atomic_set_property)
> > 		return crtc->funcs->atomic_set_property(crtc, state, property, val);
> > 	else
> > @@ -532,6 +534,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc,
> > 		*val = (state->ctm) ? state->ctm->base.id : 0;
> > 	else if (property == config->gamma_lut_property)
> > 		*val = (state->gamma_lut) ? state->gamma_lut->base.id : 0;
> > +	else if (property == config->prop_out_fence_ptr)
> > +		*val = 0;
> > 	else if (crtc->funcs->atomic_get_property)
> > 		return crtc->funcs->atomic_get_property(crtc, state, property, val);
> > 	else
> > @@ -1474,11 +1478,9 @@ EXPORT_SYMBOL(drm_atomic_nonblocking_commit);
> >  */
> > 
> > static struct drm_pending_vblank_event *create_vblank_event(
> > -		struct drm_device *dev, struct drm_file *file_priv,
> > -		struct fence *fence, uint64_t user_data)
> > +		struct drm_device *dev, uint64_t user_data)
> > {
> > 	struct drm_pending_vblank_event *e = NULL;
> > -	int ret;
> > 
> > 	e = kzalloc(sizeof *e, GFP_KERNEL);
> > 	if (!e)
> > @@ -1488,17 +1490,6 @@ static struct drm_pending_vblank_event *create_vblank_event(
> > 	e->event.base.length = sizeof(e->event);
> > 	e->event.user_data = user_data;
> > 
> > -	if (file_priv) {
> > -		ret = drm_event_reserve_init(dev, file_priv, &e->base,
> > -					     &e->event.base);
> > -		if (ret) {
> > -			kfree(e);
> > -			return NULL;
> > -		}
> > -	}
> > -
> > -	e->base.fence = fence;
> > -
> > 	return e;
> > }
> > 
> > @@ -1603,6 +1594,40 @@ void drm_atomic_clean_old_fb(struct drm_device *dev,
> > }
> > EXPORT_SYMBOL(drm_atomic_clean_old_fb);
> > 
> > +static int crtc_setup_out_fence(struct drm_crtc *crtc,
> > +				struct drm_crtc_state *crtc_state,
> > +				struct drm_out_fence_state *fence_state)
> > +{
> > +	struct fence *fence;
> > +
> > +	fence_state->fd = get_unused_fd_flags(O_CLOEXEC);
> > +	if (fence_state->fd < 0) {
> > +		return fence_state->fd;
> > +	}
> > +
> > +	fence_state->out_fence_ptr = crtc_state->out_fence_ptr;
> > +	crtc_state->out_fence_ptr = NULL;
> > +
> > +	if (put_user(fence_state->fd, fence_state->out_fence_ptr))
> > +		return -EFAULT;
> > +
> > +	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> > +	if (!fence)
> > +		return -ENOMEM;
> > +
> > +	fence_init(fence, &drm_crtc_fence_ops, &crtc->fence_lock,
> > +		   crtc->fence_context, ++crtc->fence_seqno);
> > +
> > +	fence_state->sync_file = sync_file_create(fence);
> > +	if(!fence_state->sync_file) {
> > +		fence_put(fence);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	crtc_state->event->base.fence = fence_get(fence);
> > +	return 0;
> > +}
> > +
> > int drm_mode_atomic_ioctl(struct drm_device *dev,
> > 			  void *data, struct drm_file *file_priv)
> > {
> > @@ -1617,9 +1642,10 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
> > 	struct drm_plane *plane;
> > 	struct drm_crtc *crtc;
> > 	struct drm_crtc_state *crtc_state;
> > +	struct drm_out_fence_state *fence_state;
> > 	unsigned plane_mask;
> > 	int ret = 0;
> > -	unsigned int i, j;
> > +	unsigned int i, j, fence_idx = 0;
> > 
> > 	/* disallow for drivers not supporting atomic: */
> > 	if (!drm_core_check_feature(dev, DRIVER_ATOMIC))
> > @@ -1734,12 +1760,19 @@ retry:
> > 		drm_mode_object_unreference(obj);
> > 	}
> > 
> > -	if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> > -		for_each_crtc_in_state(state, crtc, crtc_state, i) {
> > +	fence_state = kcalloc(dev->mode_config.num_crtc, sizeof(*fence_state),
> > +			      GFP_KERNEL);
> > +	if (!fence_state) {
> > +		ret = -ENOMEM;
> > +		goto out;
> > +	}
> > +
> > +	for_each_crtc_in_state(state, crtc, crtc_state, i) {
> > +		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT ||
> > +		    crtc_state->out_fence_ptr) {
> > 			struct drm_pending_vblank_event *e;
> > 
> > -			e = create_vblank_event(dev, file_priv, NULL,
> > -						arg->user_data);
> > +			e = create_vblank_event(dev, arg->user_data);
> > 			if (!e) {
> > 				ret = -ENOMEM;
> > 				goto out;
> > @@ -1747,6 +1780,28 @@ retry:
> > 
> > 			crtc_state->event = e;
> > 		}
> > +
> > +		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> > +			struct drm_pending_vblank_event *e = crtc_state->event;
> > +
> > +			if (!file_priv)
> > +				continue;
> > +
> > +			ret = drm_event_reserve_init(dev, file_priv, &e->base,
> > +						     &e->event.base);
> > +			if (ret) {
> > +				kfree(e);
> > +				crtc_state->event = NULL;
> > +				goto out;
> > +			}
> > +		}
> > +
> > +		if (crtc_state->out_fence_ptr) {
> > +			ret = crtc_setup_out_fence(crtc, crtc_state,
> > +						   &fence_state[fence_idx++]);
> > +			if (ret)
> > +				goto out;
> > +		}
> > 	}
> > 
> > 	if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY) {
> > @@ -1761,24 +1816,37 @@ retry:
> > 		ret = drm_atomic_commit(state);
> > 	}
> > 
> > +	for (i = 0; i < fence_idx; i++)
> > +		fd_install(fence_state[i].fd, fence_state[i].sync_file->file);
> > +
> > out:
> > 	drm_atomic_clean_old_fb(dev, plane_mask, ret);
> > 
> > -	if (ret && arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> > +	for_each_crtc_in_state(state, crtc, crtc_state, i) {
> 
> I think a check on ret is still needed before you iterate the CRTCs.
> If the commit is successful then state has already been freed by this
> point, and I get a splat.

Yes, I believe I only tested with non-blocking requests.

> 
> > 		/*
> > 		 * TEST_ONLY and PAGE_FLIP_EVENT are mutually exclusive,
> > 		 * if they weren't, this code should be called on success
> > 		 * for TEST_ONLY too.
> > 		 */
> > +		if (ret && crtc_state->event)
> > +			drm_event_cancel_free(dev, &crtc_state->event->base);
> > +	}
> > 
> > -		for_each_crtc_in_state(state, crtc, crtc_state, i) {
> > -			if (!crtc_state->event)
> > -				continue;
> > +	if (ret && fence_state) {
> > +		for (i = 0; i < fence_idx; i++) {
> > +			if (fence_state[i].fd >= 0)
> > +				put_unused_fd(fence_state[i].fd);
> > +			if (fence_state[i].sync_file)
> > +				fput(fence_state[i].sync_file->file);
> > 
> > -			drm_event_cancel_free(dev, &crtc_state->event->base);
> > +			/* If this fails, there's not much we can do about it */
> > +			if (put_user(-1, fence_state->out_fence_ptr))
> > +				DRM_ERROR("Couldn't clear out_fence_ptr\n");
> > 		}
> > 	}
> > 
> > +	kfree(fence_state);
> > +
> > 	if (ret == -EDEADLK) {
> > 		drm_atomic_state_clear(state);
> > 		drm_modeset_backoff(&ctx);
> > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > index b99090f..40bce97 100644
> > --- a/drivers/gpu/drm/drm_crtc.c
> > +++ b/drivers/gpu/drm/drm_crtc.c
> > @@ -274,6 +274,8 @@ int drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc,
> > 	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
> > 		drm_object_attach_property(&crtc->base, config->prop_active, 0);
> > 		drm_object_attach_property(&crtc->base, config->prop_mode_id, 0);
> > +		drm_object_attach_property(&crtc->base,
> > +					   config->prop_out_fence_ptr, 0);
> > 	}
> > 
> > 	return 0;
> > @@ -434,6 +436,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
> > 		return -ENOMEM;
> > 	dev->mode_config.prop_in_fence_fd = prop;
> > 
> > +	prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC,
> > +			"OUT_FENCE_PTR", 0, U64_MAX);
> > +	if (!prop)
> > +		return -ENOMEM;
> > +	dev->mode_config.prop_out_fence_ptr = prop;
> > +
> > 	prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC,
> > 			"CRTC_ID", DRM_MODE_OBJECT_CRTC);
> > 	if (!prop)
> > diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> > index 657a33a..b898604 100644
> > --- a/include/drm/drm_crtc.h
> > +++ b/include/drm/drm_crtc.h
> > @@ -165,6 +165,8 @@ struct drm_crtc_state {
> > 	struct drm_property_blob *ctm;
> > 	struct drm_property_blob *gamma_lut;
> > 
> > +	u64 __user *out_fence_ptr;
> > +
> 
> I'm somewhat not convinced about stashing a __user pointer in the
> CRTC atomic state. I know it gets cleared before the driver sees it,
> but if anything I think that hints that this isn't the right place to
> store it.
> 
> I've been trying to think of other ways to get from a property to
> something drm_mode_atomic_ioctl can use - maybe we can store some
> stuff in drm_atomic_state which only lives for the length of the ioctl
> call and put this pointer in there.

The drm_atomic_state is still visible by the drivers. Between there and
crtc_state, I would keep in the crtc_state for now.

Gustavo