[Freedreno] [PATCH v2 5/5] drm/msm: subclass work object for vblank events
Jeykumar Sankaran
jsanka at codeaurora.org
Tue Nov 20 22:04:14 UTC 2018
On 2018-11-07 07:55, Sean Paul wrote:
> On Tue, Nov 06, 2018 at 02:36:30PM -0800, Jeykumar Sankaran wrote:
>> msm maintains a separate structure to define vblank
>> work definitions and a list to track events submitted
>> to the workqueue. We can avoid this redundant list
>> and its protection mechanism, if we subclass the
>> work object to encapsulate vblank event parameters.
>>
>> changes in v2:
>> - subclass optimization on system wq (Sean Paul)
>
> I wouldn't do it like this, tbh. One problem is that you've lost your
> flush() on
> unbind, so there's no way to know if you have workers in the wild
> waiting
> to
> enable/disable vblank.
>
> Another issues is that AFAICT, we don't need a queue of
> enables/disables,
> but
> rather just the last requested state (ie: should we be on or off). So
> things
> don't need to be this complicated (and we're possibly thrashing vblank
> on/off
> for no reason).
>
> I'm still of the mind that you should just make this synchronous and be
> done
> with the threads (especially since we're still uncovering/introducing
> races!).
>
While scoping out the effort to make vblank events synchronous, I found
that the spinlock locking order of vblank request sequence and vblank
callback
sequences are the opposite.
In DPU, drm_vblank_enable acquires vblank_time_lock before registering
the crtc to encoder which happens after acquiring encoder_spinlock. But
the vblank_callback acquires encoder_spinlock before accessing the
registered
crtc and calling into drm_vblank_handler which tries to acquire
vblank_time_lock.
Acquiring both vblank_time_lock and encoder_spinlock in the same thread
is leading to deadlock.
In MDP5, I see the same pattern between vblank_time_lock and list_lock
which
is used to track the irq handlers.
I believe that explains why msm_drv is queuing the vblank enable/disable
works to WQ after acquiring vblank_time_lock.
Thanks,
Jeykumar S.
> Sean
>
>>
>> Signed-off-by: Jeykumar Sankaran <jsanka at codeaurora.org>
>> ---
>> drivers/gpu/drm/msm/msm_drv.c | 67
> +++++++++++++------------------------------
>> drivers/gpu/drm/msm/msm_drv.h | 7 -----
>> 2 files changed, 20 insertions(+), 54 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_drv.c
> b/drivers/gpu/drm/msm/msm_drv.c
>> index 6d6c73b..8da5be2 100644
>> --- a/drivers/gpu/drm/msm/msm_drv.c
>> +++ b/drivers/gpu/drm/msm/msm_drv.c
>> @@ -203,61 +203,44 @@ u32 msm_readl(const void __iomem *addr)
>> return val;
>> }
>>
>> -struct vblank_event {
>> - struct list_head node;
>> +struct msm_vblank_work {
>> + struct work_struct work;
>> int crtc_id;
>> bool enable;
>> + struct msm_drm_private *priv;
>> };
>>
>> static void vblank_ctrl_worker(struct work_struct *work)
>> {
>> - struct msm_vblank_ctrl *vbl_ctrl = container_of(work,
>> - struct msm_vblank_ctrl,
> work);
>> - struct msm_drm_private *priv = container_of(vbl_ctrl,
>> - struct msm_drm_private,
> vblank_ctrl);
>> + struct msm_vblank_work *vbl_work = container_of(work,
>> + struct msm_vblank_work,
> work);
>> + struct msm_drm_private *priv = vbl_work->priv;
>> struct msm_kms *kms = priv->kms;
>> - struct vblank_event *vbl_ev, *tmp;
>> - unsigned long flags;
>> -
>> - spin_lock_irqsave(&vbl_ctrl->lock, flags);
>> - list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node)
> {
>> - list_del(&vbl_ev->node);
>> - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
>> -
>> - if (vbl_ev->enable)
>> - kms->funcs->enable_vblank(kms,
>> -
> priv->crtcs[vbl_ev->crtc_id]);
>> - else
>> - kms->funcs->disable_vblank(kms,
>> -
> priv->crtcs[vbl_ev->crtc_id]);
>>
>> - kfree(vbl_ev);
>> -
>> - spin_lock_irqsave(&vbl_ctrl->lock, flags);
>> - }
>> + if (vbl_work->enable)
>> + kms->funcs->enable_vblank(kms,
> priv->crtcs[vbl_work->crtc_id]);
>> + else
>> + kms->funcs->disable_vblank(kms,
> priv->crtcs[vbl_work->crtc_id]);
>>
>> - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
>> + kfree(vbl_work);
>> }
>>
>> 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;
>> + 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;
>>
>> - schedule_work(&vbl_ctrl->work);
>> + schedule_work(&vbl_work->work);
>>
>> return 0;
>> }
>> @@ -269,14 +252,13 @@ 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.
>> */
>> +
>> msm_gem_shrinker_cleanup(ddev);
>>
>> drm_kms_helper_poll_fini(ddev);
>> @@ -292,12 +274,6 @@ static int msm_drm_uninit(struct device *dev)
>> #endif
>> drm_mode_config_cleanup(ddev);
>>
>> - 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);
>> - }
>> -
>> /* clean up event worker threads */
>> for (i = 0; i < priv->num_crtcs; i++) {
>> if (priv->event_thread[i].thread) {
>> @@ -469,9 +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);
>> - 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 05d33a7..d4cbde2 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 work_struct work;
>> - struct list_head event_list;
>> - spinlock_t lock;
>> -};
>> -
>> #define MSM_GPU_MAX_RINGS 4
>> #define MAX_H_TILES_PER_DISPLAY 2
>>
>> @@ -225,7 +219,6 @@ 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
>>
>> _______________________________________________
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>> Freedreno at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/freedreno
--
Jeykumar S
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