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

Sean Paul
2018-11-01T19:18:38Z

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;
> };
>
> --
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> a Linux Foundation Collaborative Project
>
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--
Sean Paul, Software Engineer, Google / Chromium OS