Message-ID: <2a7b8d46a0358dfe538de1299d2d7c5c5c3ab626.camel@mediatek.com>
Date: Tue, 20 Aug 2024 05:56:14 +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>,
	"angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>
CC: "linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	Singo Chang (張興國) <Singo.Chang@...iatek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
	"daniel@...ll.ch" <daniel@...ll.ch>, "p.zabel@...gutronix.de"
	<p.zabel@...gutronix.de>, Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"airlied@...il.com" <airlied@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] drm/mediatek: Fix missing configuration flags in
 mtk_crtc_ddp_config()

Hi, Jason:

On Mon, 2024-08-19 at 23:25 +0800, Jason-JH.Lin via B4 Relay wrote:
>  	 
> External email : Please do not click links or open attachments until you have verified the sender or the content.
>  From: "Jason-JH.Lin" <jason-jh.lin@...iatek.com>
> 
> In mtk_crtc_ddp_config(), mtk_crtc will use some configuration flags to
> generate instructions to cmdq_handle, such as:
>   state->pending_config
>   mtk_crtc->pending_planes
>   plane_state->pending.config
>   mtk_crtc->pending_async_planes
>   plane_state->pending.async_config
> 
> These configuration flags may be set to false when a GCE IRQ comes calling
> ddp_cmdq_cb(). This may result in missing prepare instructions,
> especially if mtk_crtc_update_config() with the flase need_vblank (no need
> to wait for vblank) cases.
> 
> Therefore, the mtk_crtc->config_updating flag is set at the beginning of
> mtk_crtc_update_config() to ensure that these configuration flags won't be
> changed when the mtk_crtc_ddp_config() is preparing instructions.
> But somehow the ddp_cmdq_cb() didn't use the mtk_crtc->config_updating
> flag to prevent those pending config flags from being cleared.
> 
> To avoid missing the configuration when generating the config instruction,
> the config_updating flag should be added into ddp_cmdq_cb() and be
> protected with spin_lock.

Reviewed-by: CK Hu <ck.hu@...iatek.com>

> 
> Fixes: 7f82d9c43879 ("drm/mediatek: Clear pending flag when cmdq packet is done")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> ---
> Change in v2:
> Add spin_lock protection for config_updating flag.
> ---
>  drivers/gpu/drm/mediatek/mtk_crtc.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_crtc.c b/drivers/gpu/drm/mediatek/mtk_crtc.c
> index 6f34f573e127..b752c0b46383 100644
> --- a/drivers/gpu/drm/mediatek/mtk_crtc.c
> +++ b/drivers/gpu/drm/mediatek/mtk_crtc.c
> @@ -69,6 +69,8 @@ struct mtk_crtc {
>  /* lock for display hardware access */
>  struct mutexhw_lock;
>  boolconfig_updating;
> +/* lock for config_updating to cmd buffer */
> +spinlock_tconfig_lock;
>  };
>  
>  struct mtk_crtc_state {
> @@ -107,10 +109,13 @@ static void mtk_crtc_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
>  {
>  drm_crtc_handle_vblank(&mtk_crtc->base);
> +
> +spin_lock(&mtk_crtc->config_lock);
>  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(&mtk_crtc->config_lock);
>  }
>  
>  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
> @@ -314,6 +319,13 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>  
>  state = to_mtk_crtc_state(mtk_crtc->base.state);
>  
> +spin_lock(&mtk_crtc->config_lock);
> +
> +if (mtk_crtc->config_updating) {
> +spin_unlock(&mtk_crtc->config_lock);
> +goto ddp_cmdq_cb_out;
> +}
> +
>  state->pending_config = false;
>  
>  if (mtk_crtc->pending_planes) {
> @@ -340,6 +352,10 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
>  mtk_crtc->pending_async_planes = false;
>  }
>  
> +spin_unlock(&mtk_crtc->config_lock);
> +
> +ddp_cmdq_cb_out:
> +
>  mtk_crtc->cmdq_vblank_cnt = 0;
>  wake_up(&mtk_crtc->cb_blocking_queue);
>  }
> @@ -571,7 +587,11 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
>  int i;
>  
>  mutex_lock(&mtk_crtc->hw_lock);
> +
> +spin_lock(&mtk_crtc->config_lock);
>  mtk_crtc->config_updating = true;
> +spin_unlock(&mtk_crtc->config_lock);
> +
>  if (needs_vblank)
>  mtk_crtc->pending_needs_vblank = true;
>  
> @@ -625,7 +645,10 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
>  mbox_client_txdone(mtk_crtc->cmdq_client.chan, 0);
>  }
>  #endif
> +spin_lock(&mtk_crtc->config_lock);
>  mtk_crtc->config_updating = false;
> +spin_unlock(&mtk_crtc->config_lock);
> +
>  mutex_unlock(&mtk_crtc->hw_lock);
>  }
>  
> @@ -1068,6 +1091,7 @@ int mtk_crtc_create(struct drm_device *drm_dev, const unsigned int *path,
>  drm_mode_crtc_set_gamma_size(&mtk_crtc->base, gamma_lut_size);
>  drm_crtc_enable_color_mgmt(&mtk_crtc->base, 0, has_ctm, gamma_lut_size);
>  mutex_init(&mtk_crtc->hw_lock);
> +spin_lock_init(&mtk_crtc->config_lock);
>  
>  #if IS_REACHABLE(CONFIG_MTK_CMDQ)
>  i = priv->mbox_index++;
> 
> ---
> base-commit: 469f1bad3c1c6e268059f78c0eec7e9552b3894c
> change-id: 20240819-drm-fixup-0819-f51e2d37fcd7
> 
> Best regards,
> -- 
> Jason-JH.Lin <jason-jh.lin@...iatek.com>
> 
> 

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