[DPU PATCH 06/11] drm/msm: Remove msm_commit/kthread, use atomic helper commit
Sean Paul
seanpaul at chromium.org
Fri Mar 2 14:56:46 UTC 2018
On Thu, Mar 01, 2018 at 07:37:10PM -0500, Rob Clark wrote:
> On Thu, Mar 1, 2018 at 3:37 PM, <jsanka at codeaurora.org> wrote:
> > On 2018-03-01 07:27, Sean Paul wrote:
> >>
> >> On Wed, Feb 28, 2018 at 08:07:00PM -0800, jsanka at 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 at 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.
>
> I think a good example to think about is virtualizing hwpipe<->plane
> mapping, for example, when you need to re-assign hwpipes for the next
> frame according to what capabilities are needed (yuv, scaling) or gang
> up two hwpipes for wide buffer scanout (or re-use one hwpipe for two
> planes).. in mdp5 we keep track of what hwpipes are in use by which
> planes in driver global atomic state (I have some revived patches from
> architt to convert this to driver private objs)..
>
> With the atomic model we have serialization in the (to abuse some
> terms) "top half" (ie. userspace calling into ioctl) by virtue of the
> modeset locks. But there is a second half to this. Because we update
> the new incoming global state object about what hwpipes are released
> in atomic_check, if the incoming state is committed/swapped in the
> "top half" we rely on this state being valid in the "bottom half" (in
> this case the wq) before pushing the new state to the hw.. which
> essentially forces us to serialize committing the state in the "bottom
> half" so things happen in the same order as the "top half" intended.
> Otherwise we could try to assign a hwpipe to a different crtc while it
> is still scanning out for it's previous crtc. If you have a 30Hz
> display plus a 120Hz display, I guess this is a bit sub-optimal.
It's still bad even with displays refreshing at the same rate, the worst case
could halve the refresh rate if vblanks aren't in sync.
>
> Maybe the answer is per-crtc wq's for commits plus some sort of
> fencing scheme to stall things when there are cross-crtc dependencies
> (ie. commit on crtc B depends on hwpipe released by commit on crtc A)?
> This way we don't block updates on the faster display when it isn't
> required. I'm not quite sure how that would work. But perhaps at
> least we could somehow allow out-of-order commits when two updates
> don't touch any of the same state obj's.
Right, for "normal" updates, you could use the fast path. We already have
needs_modeset, so adding needs_sync wouldn't be too bad. I think I ran into this
with tegra back in Pixel C days and hacked in a per-crtc worker since the
resources were statically mapped. We'll probably run into this in CrOS as we
expand our explicit sync support in the compositor.
>
> (But I do think this is something we should discuss on dri-devel, and
> I'd prefer do solve this in the atomic helpers, rather than having
> userspace workaround different sets of bugs/quirks for each different
> driver. It really isn't something that is hw specific, so it doesn't
> belong in the driver.)
Agreed, this is a tricky bit of code and it would benefit from being used across
all drivers (as well as all drivers benefiting from it). At any rate, I can't
use multi-display on my development device right now, so I think we'll need to
defer for now.
Sean
>
> BR,
> -R
>
>
> > "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];
--
Sean Paul, Software Engineer, Google / Chromium OS
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