On Thu, Mar 01, 2018 at 07:37:10PM -0500, Rob Clark wrote:
On Thu, Mar 1, 2018 at 3:37 PM, <jsanka@xxxxxxxxxxxxxx> wrote:
> On 2018-03-01 07:27, Sean Paul wrote:
>>
>> On Wed, Feb 28, 2018 at 08:07:00PM -0800, jsanka@xxxxxxxxxxxxxx
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@xxxxxxxxxxxx>
>>> > ---
>>> > 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];
