linux-kernel - Re: [PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq

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Message-ID: <c0092a07a9e6d0bc9b2dc85f379e6cddfa095ef7.camel@mediatek.com>
Date: Fri, 6 Dec 2024 09:28:47 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>,
	"chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>
CC: Singo Chang (張興國) <Singo.Chang@...iatek.com>,
	Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-mediatek@...ts.infradead.org"
	<linux-mediatek@...ts.infradead.org>, "fshao@...omium.org"
	<fshao@...omium.org>, Shawn Sung (宋孝謙)
	<Shawn.Sung@...iatek.com>
Subject: Re: [PATCH v2] drm/mediatek: Move mtk_crtc_finish_page_flip() to
 ddp_cmdq_cb()

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@...iatek.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);
>  }