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

[Sean Paul <sean-p7yTbzM4H96eqtR555YLDQ@public.gmane.org>]

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
> @@ -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 kthread_work work;
>  	int crtc_id;
>  	bool enable;
> +	struct msm_drm_private *priv;
>  };
>  
>  static void vblank_ctrl_worker(struct kthread_work *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;
> +	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.

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.

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