[PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq_cb()

[PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq_cb()

[Jason-JH.Lin]

mtk_crtc_finish_page_flip() is used to notify userspace that a
page flip has been completed, allowing userspace to free the frame
buffer of the last frame and commit the next frame.

In MediaTek's hardware design for configuring display hardware by using
GCE, `DRM_EVENT_FLIP_COMPLETE` should be notified to userspace after
GCE has finished configuring all display hardware settings for each
atomic_commit().

Currently, mtk_crtc_finish_page_flip() cannot guarantee that GCE has
configured all the display hardware settings of the last frame.
Therefore, to increase the accuracy of the timing for notifying
`DRM_EVENT_FLIP_COMPLETE` to userspace, mtk_crtc_finish_page_flip()
should be moved to ddp_cmdq_cb().

Fixes: 7f82d9c43879 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
---
 drivers/gpu/drm/mediatek/mtk_crtc.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
index eb0e1233ad04..0d57863c075a 100644
--- a/drivers/gpu/drm/mediatek/mtk_crtc.c
+++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
@@ -109,15 +109,19 @@ static void mtk_crtc_finish_page_flip(struct mtk_crtc *mtk_crtc)
 static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
 {
 	unsigned long flags;
+	struct drm_crtc *crtc = &mtk_crtc->base;
+	struct mtk_drm_private *priv = crtc->dev->dev_private;
 
 	drm_crtc_handle_vblank(&mtk_crtc->base);
 
-	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
-	if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
-		mtk_crtc_finish_page_flip(mtk_crtc);
-		mtk_crtc->pending_needs_vblank = false;
+	if (priv->data->shadow_register) {
+		spin_lock_irqsave(&mtk_crtc->config_lock, flags);
+		if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
+			mtk_crtc_finish_page_flip(mtk_crtc);
+			mtk_crtc->pending_needs_vblank = false;
+		}
+		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
 	}
-	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
 }
 
 static void mtk_crtc_destroy(struct drm_crtc *crtc)
@@ -284,10 +288,8 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
 	state = to_mtk_crtc_state(mtk_crtc->base.state);
 
 	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
-	if (mtk_crtc->config_updating) {
-		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+	if (mtk_crtc->config_updating)
 		goto ddp_cmdq_cb_out;
-	}
 
 	state->pending_config = false;
 
@@ -315,10 +317,15 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
 		mtk_crtc->pending_async_planes = false;
 	}
 
-	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
-
 ddp_cmdq_cb_out:
 
+	if (mtk_crtc->pending_needs_vblank) {
+		mtk_crtc_finish_page_flip(mtk_crtc);
+		mtk_crtc->pending_needs_vblank = false;
+	}
+
+	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+
 	mtk_crtc->cmdq_vblank_cnt = 0;
 	wake_up(&mtk_crtc->cb_blocking_queue);
 }
-- 
2.43.0

Re: [PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq_cb()

[CK Hu (胡俊光)]

Hi, Jason:

On Wed, 2024-11-20 at 00:36 +0800, Jason-JH.Lin wrote:
> mtk_crtc_finish_page_flip() is used to notify userspace that a
> page flip has been completed, allowing userspace to free the frame
> buffer of the last frame and commit the next frame.
> 
> In MediaTek's hardware design for configuring display hardware by using
> GCE, `DRM_EVENT_FLIP_COMPLETE` should be notified to userspace after
> GCE has finished configuring all display hardware settings for each
> atomic_commit().
> 
> Currently, mtk_crtc_finish_page_flip() cannot guarantee that GCE has
> configured all the display hardware settings of the last frame.
> Therefore, to increase the accuracy of the timing for notifying
> `DRM_EVENT_FLIP_COMPLETE` to userspace, mtk_crtc_finish_page_flip()
> should be moved to ddp_cmdq_cb().
> 
> Fixes: 7f82d9c43879 ("drm/mediatek: Clear pending flag when cmdq packet is done")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_crtc.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
> index eb0e1233ad04..0d57863c075a 100644
> --- a/drivers/gpu/drm/mediatek/mtk_crtc.c
> +++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
> @@ -109,15 +109,19 @@ static void mtk_crtc_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  {
>  	unsigned long flags;
> +	struct drm_crtc *crtc = &mtk_crtc->base;
> +	struct mtk_drm_private *priv = crtc->dev->dev_private;
>  
>  	drm_crtc_handle_vblank(&mtk_crtc->base);
>  
> -	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> -	if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
> -		mtk_crtc_finish_page_flip(mtk_crtc);
> -		mtk_crtc->pending_needs_vblank = false;
> +	if (priv->data->shadow_register) {

if (!priv->data->shadow_register)
	return;

And this would reduce the indent.

> +		spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> +		if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
> +			mtk_crtc_finish_page_flip(mtk_crtc);
> +			mtk_crtc->pending_needs_vblank = false;
> +		}
> +		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
>  	}
> -	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
>  }
>  
>  static void mtk_crtc_destroy(struct drm_crtc *crtc)
> @@ -284,10 +288,8 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>  	state = to_mtk_crtc_state(mtk_crtc->base.state);
>  
>  	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> -	if (mtk_crtc->config_updating) {
> -		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> +	if (mtk_crtc->config_updating)
>  		goto ddp_cmdq_cb_out;
> -	}
>  
>  	state->pending_config = false;
>  
> @@ -315,10 +317,15 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>  		mtk_crtc->pending_async_planes = false;
>  	}
>  
> -	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> -
>  ddp_cmdq_cb_out:
>  
> +	if (mtk_crtc->pending_needs_vblank) {
> +		mtk_crtc_finish_page_flip(mtk_crtc);
> +		mtk_crtc->pending_needs_vblank = false;

In mtk_crtc_update_config(), after mbox_client_txdone() and before mtk_crtc->config_updating = false;
cmdq may have finish the command and callback ddp_cmdq_cb().
Because mtk_crtc->config_updating is true, so this page flip would be skipped.
But if there is no next mtk_crtc_update_config() exist, this page flip would never happen.
This may cause some deadlock.

Regards,
CK

> +	}
> +
> +	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> +
>  	mtk_crtc->cmdq_vblank_cnt = 0;
>  	wake_up(&mtk_crtc->cb_blocking_queue);
>  }

Re: [PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq_cb()

[Jason-JH Lin (林睿祥)]

Hi CK,

Thanks for the review.

[snip]

> >  static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
> >  {
> >  	unsigned long flags;
> > +	struct drm_crtc *crtc = &mtk_crtc->base;
> > +	struct mtk_drm_private *priv = crtc->dev->dev_private;
> >  
> >  	drm_crtc_handle_vblank(&mtk_crtc->base);
> >  
> > -	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> > -	if (!mtk_crtc->config_updating && mtk_crtc-
> > >pending_needs_vblank) {
> > -		mtk_crtc_finish_page_flip(mtk_crtc);
> > -		mtk_crtc->pending_needs_vblank = false;
> > +	if (priv->data->shadow_register) {
> 
> if (!priv->data->shadow_register)
> 	return;
> 
> And this would reduce the indent.
> 

OK, I'll adjust this.

> > +		spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> > +		if (!mtk_crtc->config_updating && mtk_crtc-
> > >pending_needs_vblank) {
> > +			mtk_crtc_finish_page_flip(mtk_crtc);
> > +			mtk_crtc->pending_needs_vblank = false;
> > +		}
> > +		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> >  	}
> > -	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> >  }
> >  
> >  static void mtk_crtc_destroy(struct drm_crtc *crtc)
> > @@ -284,10 +288,8 @@ static void ddp_cmdq_cb(struct mbox_client
> > *cl, void *mssg)
> >  	state = to_mtk_crtc_state(mtk_crtc->base.state);
> >  
> >  	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
> > -	if (mtk_crtc->config_updating) {
> > -		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> > +	if (mtk_crtc->config_updating)
> >  		goto ddp_cmdq_cb_out;
> > -	}
> >  
> >  	state->pending_config = false;
> >  
> > @@ -315,10 +317,15 @@ static void ddp_cmdq_cb(struct mbox_client
> > *cl, void *mssg)
> >  		mtk_crtc->pending_async_planes = false;
> >  	}
> >  
> > -	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
> > -
> >  ddp_cmdq_cb_out:
> >  
> > +	if (mtk_crtc->pending_needs_vblank) {
> > +		mtk_crtc_finish_page_flip(mtk_crtc);
> > +		mtk_crtc->pending_needs_vblank = false;
> 
> In mtk_crtc_update_config(), after mbox_client_txdone() and before
> mtk_crtc->config_updating = false;
> cmdq may have finish the command and callback ddp_cmdq_cb().
> Because mtk_crtc->config_updating is true, so this page flip would be
> skipped.
> But if there is no next mtk_crtc_update_config() exist, this page
> flip would never happen.
> This may cause some deadlock.
> 

OK, I'll move the mtk_crtc->config_updating = false; earlier than 
mbox_client_txdone() to avoid skipping the page flip.

Regards,
Jason-JH.Lin

> Regards,
> CK