Re: [Freedreno] [PATCH 2/2] drm/msm: subclass work object for vblank events

Sean Paul
2018-11-05T17:24:21Z

On Fri, Nov 02, 2018 at 04:38:48PM -0700, Jeykumar Sankaran wrote:
> On 2018-11-01 12:18, Sean Paul wrote:
> > On Wed, Oct 31, 2018 at 05:19:05PM -0700, Jeykumar Sankaran wrote:
> > > msm maintains a separate structure to define vblank
> > > work definitions and a list to track events submitted
> > > to the display worker thread. We can avoid these
> > > redundant list and its protection mechanism, if we
> > > subclass the work object to encapsulate vblank
> > > event parameters.
> > >
> > > Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
> > > ---
> > > drivers/gpu/drm/msm/msm_drv.c | 70
> > ++++++++++++-------------------------------
> > > drivers/gpu/drm/msm/msm_drv.h | 7 -----
> > > 2 files changed, 19 insertions(+), 58 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.c
> > b/drivers/gpu/drm/msm/msm_drv.c
> > > index 1f384b3..67a96ee 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > +++ b/drivers/gpu/drm/msm/msm_drv.c

/snip

> > > static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
> > > int crtc_id, bool enable)
> > > {
> > > - struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> > > - struct vblank_event *vbl_ev;
> > > - unsigned long flags;
> > > + struct msm_vblank_work *vbl_work;
> > >
> > > - vbl_ev = kzalloc(sizeof(*vbl_ev), GFP_ATOMIC);
> > > - if (!vbl_ev)
> > > + vbl_work = kzalloc(sizeof(*vbl_work), GFP_ATOMIC);
> > > + if (!vbl_work)
> > > return -ENOMEM;
> > >
> > > - vbl_ev->crtc_id = crtc_id;
> > > - vbl_ev->enable = enable;
> > > + kthread_init_work(&vbl_work->work, vblank_ctrl_worker);
> > >
> > > - spin_lock_irqsave(&vbl_ctrl->lock, flags);
> > > - list_add_tail(&vbl_ev->node, &vbl_ctrl->event_list);
> > > - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> > > + vbl_work->crtc_id = crtc_id;
> > > + vbl_work->enable = enable;
> > > + vbl_work->priv = priv;
> > >
> > > - kthread_queue_work(&priv->disp_thread.worker, &vbl_ctrl->work);
> > > + kthread_queue_work(&priv->disp_thread.worker, &vbl_work->work);
> >
> > So I think this can get even more simplified. In the short term, you can
> > just
> > use the systemwq to do the enable and disable.
>
> you mean priv->wq?
>

I meant the system workqueue, we probably don't need our own for this.

> >
> > In the long term, the enable_vblank/disable_vblank functions should be
> > optimized so they don't sleep. I took a quick look at them perhaps this
> > is
> > all because of the crtc_lock mutex? That lock seems a bit suspicious to
> > me,
> > especially being dropped around the pm_runtime calls in
> > _dpu_crtc_vblank_enable_no_lock(). I think we could probably rely on the
> > modeset
> > locks for some of these functions, and perhaps convert it to a spinlock
> > if
> > we
> > can't get rid of it entirely.
>
> crtc_lock has a history of usage in the downstream driver. It was introduced
> to protect
> vblank variables when vblank requests were handled in the user thread
> (not the display thread). When event threads were introduced to receive
> encoder events, the lock was further expanded to protect few more vars. It
> was
> also needed to synchronize CRTC accesses between debugfs dump calls
> and display thread.

The debugfs case can be solved pretty easily by using the modeset locks. I
haven't looked closely at the event threads, could we convert crtc_lock to a
spinlock and then make vblank enable/disable synchronous?

Sean

>
> Would like to deal with this cleanup bit later once we lose these extra
> threads.
>
> Thanks and Regards,
> Jeykumar S.
>
> >
> > Sean
> >
> > >
> > > return 0;
> > > }
> > > @@ -269,20 +252,8 @@ static int msm_drm_uninit(struct device *dev)
> > > struct msm_drm_private *priv = ddev->dev_private;
> > > struct msm_kms *kms = priv->kms;
> > > struct msm_mdss *mdss = priv->mdss;
> > > - struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> > > - struct vblank_event *vbl_ev, *tmp;
> > > int i;
> > >
> > > - /* We must cancel and cleanup any pending vblank enable/disable
> > > - * work before drm_irq_uninstall() to avoid work re-enabling an
> > > - * irq after uninstall has disabled it.
> > > - */
> > > - kthread_flush_work(&vbl_ctrl->work);
> > > - list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node)
> > {
> > > - list_del(&vbl_ev->node);
> > > - kfree(vbl_ev);
> > > - }
> > > -
> > > kthread_flush_worker(&priv->disp_thread.worker);
> > > kthread_stop(priv->disp_thread.thread);
> > > priv->disp_thread.thread = NULL;
> > > @@ -474,9 +445,6 @@ static int msm_drm_init(struct device *dev, struct
> > drm_driver *drv)
> > > priv->wq = alloc_ordered_workqueue("msm", 0);
> > >
> > > INIT_LIST_HEAD(&priv->inactive_list);
> > > - INIT_LIST_HEAD(&priv->vblank_ctrl.event_list);
> > > - kthread_init_work(&priv->vblank_ctrl.work, vblank_ctrl_worker);
> > > - spin_lock_init(&priv->vblank_ctrl.lock);
> > >
> > > drm_mode_config_init(ddev);
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.h
> > b/drivers/gpu/drm/msm/msm_drv.h
> > > index e81b1fa..b91e306 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.h
> > > +++ b/drivers/gpu/drm/msm/msm_drv.h
> > > @@ -77,12 +77,6 @@ enum msm_mdp_plane_property {
> > > PLANE_PROP_MAX_NUM
> > > };
> > >
> > > -struct msm_vblank_ctrl {
> > > - struct kthread_work work;
> > > - struct list_head event_list;
> > > - spinlock_t lock;
> > > -};
> > > -
> > > #define MSM_GPU_MAX_RINGS 4
> > > #define MAX_H_TILES_PER_DISPLAY 2
> > >
> > > @@ -226,7 +220,6 @@ struct msm_drm_private {
> > > struct notifier_block vmap_notifier;
> > > struct shrinker shrinker;
> > >
> > > - struct msm_vblank_ctrl vblank_ctrl;
> > > struct drm_atomic_state *pm_state;
> > > };
> > >
> > > --
> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
> > Forum,
> > > a Linux Foundation Collaborative Project
> > >
> > > _______________________________________________
> > > Freedreno mailing list
> > > Freedreno@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/freedreno
>
> --
> Jeykumar S

--
Sean Paul, Software Engineer, Google / Chromium OS
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