[PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list

[PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list

[Marek Szyprowski]

Exynos DSI DRM driver uses private calls to out bridge to force certain
order of operations during init/exit sequences. This no longer works after
conversion of bridge chain to a double-linked list. To fix the regression
call bridge related operations manually instead of the generic
drm_bridge_chain_*() operations.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
---
This patch is a result of the following discussion:
https://www.spinics.net/lists/dri-devel/msg239256.html
---
 drivers/gpu/drm/exynos/exynos_drm_dsi.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
index 3955f84dc893..f5905c239a86 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
@@ -255,7 +255,6 @@ struct exynos_dsi {
 	struct mipi_dsi_host dsi_host;
 	struct drm_connector connector;
 	struct drm_panel *panel;
-	struct list_head bridge_chain;
 	struct drm_bridge *out_bridge;
 	struct device *dev;
 
@@ -1391,7 +1390,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
 		if (ret < 0)
 			goto err_put_sync;
 	} else {
-		drm_bridge_chain_pre_enable(dsi->out_bridge);
+		if (dsi->out_bridge->funcs->pre_enable)
+			dsi->out_bridge->funcs->pre_enable(dsi->out_bridge);
 	}
 
 	exynos_dsi_set_display_mode(dsi);
@@ -1402,7 +1402,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
 		if (ret < 0)
 			goto err_display_disable;
 	} else {
-		drm_bridge_chain_enable(dsi->out_bridge);
+		if (dsi->out_bridge->funcs->enable)
+			dsi->out_bridge->funcs->enable(dsi->out_bridge);
 	}
 
 	dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
@@ -1427,10 +1428,12 @@ static void exynos_dsi_disable(struct drm_encoder *encoder)
 	dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
 
 	drm_panel_disable(dsi->panel);
-	drm_bridge_chain_disable(dsi->out_bridge);
+	if (dsi->out_bridge->funcs->disable)
+		dsi->out_bridge->funcs->disable(dsi->out_bridge);
 	exynos_dsi_set_display_enable(dsi, false);
 	drm_panel_unprepare(dsi->panel);
-	drm_bridge_chain_post_disable(dsi->out_bridge);
+	if (dsi->out_bridge->funcs->post_disable)
+		dsi->out_bridge->funcs->post_disable(dsi->out_bridge);
 	dsi->state &= ~DSIM_STATE_ENABLED;
 	pm_runtime_put_sync(dsi->dev);
 }
@@ -1521,9 +1524,11 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
 
 	out_bridge  = of_drm_find_bridge(device->dev.of_node);
 	if (out_bridge) {
-		drm_bridge_attach(encoder, out_bridge, NULL);
+		out_bridge->dev = drm;
+		out_bridge->encoder = encoder;
+		if (out_bridge->funcs->attach)
+			out_bridge->funcs->attach(out_bridge);
 		dsi->out_bridge = out_bridge;
-		list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
 	} else {
 		int ret = exynos_dsi_create_connector(encoder);
 
@@ -1589,7 +1594,6 @@ static int exynos_dsi_host_detach(struct mipi_dsi_host *host,
 		if (dsi->out_bridge->funcs->detach)
 			dsi->out_bridge->funcs->detach(dsi->out_bridge);
 		dsi->out_bridge = NULL;
-		INIT_LIST_HEAD(&dsi->bridge_chain);
 	}
 
 	if (drm->mode_config.poll_enabled)
@@ -1737,7 +1741,6 @@ static int exynos_dsi_probe(struct platform_device *pdev)
 	init_completion(&dsi->completed);
 	spin_lock_init(&dsi->transfer_lock);
 	INIT_LIST_HEAD(&dsi->transfer_list);
-	INIT_LIST_HEAD(&dsi->bridge_chain);
 
 	dsi->dsi_host.ops = &exynos_dsi_ops;
 	dsi->dsi_host.dev = dev;
-- 
2.17.1

Re: [PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list

[Boris Brezillon]

On Fri, 27 Dec 2019 12:01:35 +0100
Marek Szyprowski <m.szyprowski@samsung.com> wrote:

> Exynos DSI DRM driver uses private calls to out bridge to force certain
> order of operations during init/exit sequences. This no longer works after
> conversion of bridge chain to a double-linked list. To fix the regression
> call bridge related operations manually instead of the generic
> drm_bridge_chain_*() operations.

I think it'd be worth explaining what the problem is (infinite loop
caused by list_for_each_entry() use when the bridge is no longer part
of the chain attached to the encoder).

> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")

We also need to fix that in VC4.

> ---
> This patch is a result of the following discussion:
> https://www.spinics.net/lists/dri-devel/msg239256.html
> ---
>  drivers/gpu/drm/exynos/exynos_drm_dsi.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index 3955f84dc893..f5905c239a86 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -255,7 +255,6 @@ struct exynos_dsi {
>  	struct mipi_dsi_host dsi_host;
>  	struct drm_connector connector;
>  	struct drm_panel *panel;
> -	struct list_head bridge_chain;
>  	struct drm_bridge *out_bridge;
>  	struct device *dev;
>  
> @@ -1391,7 +1390,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>  		if (ret < 0)
>  			goto err_put_sync;
>  	} else {
> -		drm_bridge_chain_pre_enable(dsi->out_bridge);
> +		if (dsi->out_bridge->funcs->pre_enable)
> +			dsi->out_bridge->funcs->pre_enable(dsi->out_bridge);

Okay, so you're calling ->{pre_enable,enable,disable,post_disable}() on
the first bridge element which only works if the chain contains one
bridge (see below). Maybe you should keep exynos_dsi.bridge_chain and
create custom helpers to iterate over chain elements instead of calling
those hooks only on out_bridge.

>  	}
>  
>  	exynos_dsi_set_display_mode(dsi);
> @@ -1402,7 +1402,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>  		if (ret < 0)
>  			goto err_display_disable;
>  	} else {
> -		drm_bridge_chain_enable(dsi->out_bridge);
> +		if (dsi->out_bridge->funcs->enable)
> +			dsi->out_bridge->funcs->enable(dsi->out_bridge);
>  	}
>  
>  	dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
> @@ -1427,10 +1428,12 @@ static void exynos_dsi_disable(struct drm_encoder *encoder)
>  	dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>  
>  	drm_panel_disable(dsi->panel);
> -	drm_bridge_chain_disable(dsi->out_bridge);
> +	if (dsi->out_bridge->funcs->disable)
> +		dsi->out_bridge->funcs->disable(dsi->out_bridge);
>  	exynos_dsi_set_display_enable(dsi, false);
>  	drm_panel_unprepare(dsi->panel);
> -	drm_bridge_chain_post_disable(dsi->out_bridge);
> +	if (dsi->out_bridge->funcs->post_disable)
> +		dsi->out_bridge->funcs->post_disable(dsi->out_bridge);
>  	dsi->state &= ~DSIM_STATE_ENABLED;
>  	pm_runtime_put_sync(dsi->dev);
>  }
> @@ -1521,9 +1524,11 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
>  
>  	out_bridge  = of_drm_find_bridge(device->dev.of_node);
>  	if (out_bridge) {
> -		drm_bridge_attach(encoder, out_bridge, NULL);
> +		out_bridge->dev = drm;
> +		out_bridge->encoder = encoder;
> +		if (out_bridge->funcs->attach)
> +			out_bridge->funcs->attach(out_bridge);

If you don't want to keep the dsi_exynos.bridge_chain field, you should
probably still use drm_bridge_attach() here and manually reset
encoder->bridge_chain after checking it only contains a single element.
Something like:

		drm_bridge_attach(encoder, out_bridge, NULL);

		/*
		 * FIXME: we need to control the enable/disable
		 * sequence to make sure the DSI host controller is
		 * ready to send DSI commands before the
		 * bridge->pre_enable()/panel->prepare() hooks are
		 * called (those hooks are allowed to send DSI
		 * commands). The only way to do that right now is to
		 * reset the bridge chain so that the core thinks it's
		 * empty and turns drm_bridge_chain_xxx() calls into
		 * NOPs. This only works if the chain contains only one
		 * bridge, otherwise we'd be skipping bridge->xxx()
		 * calls on other bridges which is wrong.
		 */
		WARN_ON(!list_is_singular(&encoder->bridge_chain));
		INIT_LIST_HEAD(&encoder->bridge_chain);

Calling ->attach() directly might lead to an invalid pointer
dereference if out_bridge tries to attach to another bridge
(out_bridge->bridge_node is uninitialized if you don't call
drm_bridge_attach()).

>  		dsi->out_bridge = out_bridge;
> -		list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
>  	} else {
>  		int ret = exynos_dsi_create_connector(encoder);
>  
> @@ -1589,7 +1594,6 @@ static int exynos_dsi_host_detach(struct mipi_dsi_host *host,
>  		if (dsi->out_bridge->funcs->detach)
>  			dsi->out_bridge->funcs->detach(dsi->out_bridge);
>  		dsi->out_bridge = NULL;
> -		INIT_LIST_HEAD(&dsi->bridge_chain);
>  	}
>  
>  	if (drm->mode_config.poll_enabled)
> @@ -1737,7 +1741,6 @@ static int exynos_dsi_probe(struct platform_device *pdev)
>  	init_completion(&dsi->completed);
>  	spin_lock_init(&dsi->transfer_lock);
>  	INIT_LIST_HEAD(&dsi->transfer_list);
> -	INIT_LIST_HEAD(&dsi->bridge_chain);
>  
>  	dsi->dsi_host.ops = &exynos_dsi_ops;
>  	dsi->dsi_host.dev = dev;

Re: [PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list

[Boris Brezillon]

On Fri, 27 Dec 2019 13:00:04 +0100
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> On Fri, 27 Dec 2019 12:01:35 +0100
> Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> 
> > Exynos DSI DRM driver uses private calls to out bridge to force certain
> > order of operations during init/exit sequences. This no longer works after
> > conversion of bridge chain to a double-linked list. To fix the regression
> > call bridge related operations manually instead of the generic
> > drm_bridge_chain_*() operations.  
> 
> I think it'd be worth explaining what the problem is (infinite loop
> caused by list_for_each_entry() use when the bridge is no longer part
> of the chain attached to the encoder).
> 
> > 
> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")  
> 
> We also need to fix that in VC4.
> 
> > ---
> > This patch is a result of the following discussion:
> > https://www.spinics.net/lists/dri-devel/msg239256.html
> > ---
> >  drivers/gpu/drm/exynos/exynos_drm_dsi.c | 21 ++++++++++++---------
> >  1 file changed, 12 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > index 3955f84dc893..f5905c239a86 100644
> > --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > @@ -255,7 +255,6 @@ struct exynos_dsi {
> >  	struct mipi_dsi_host dsi_host;
> >  	struct drm_connector connector;
> >  	struct drm_panel *panel;
> > -	struct list_head bridge_chain;
> >  	struct drm_bridge *out_bridge;
> >  	struct device *dev;
> >  
> > @@ -1391,7 +1390,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> >  		if (ret < 0)
> >  			goto err_put_sync;
> >  	} else {
> > -		drm_bridge_chain_pre_enable(dsi->out_bridge);
> > +		if (dsi->out_bridge->funcs->pre_enable)
> > +			dsi->out_bridge->funcs->pre_enable(dsi->out_bridge);  
> 
> Okay, so you're calling ->{pre_enable,enable,disable,post_disable}() on
> the first bridge element which only works if the chain contains one
> bridge (see below). Maybe you should keep exynos_dsi.bridge_chain and
> create custom helpers to iterate over chain elements instead of calling
> those hooks only on out_bridge.

The following diff should fix the problem while keeping the solution
generic enough to support chains containing more than one bridge.

--->8---
diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
index 3955f84dc893..c861b640fc59 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
@@ -1378,6 +1378,7 @@ static void exynos_dsi_unregister_te_irq(struct exynos_dsi *dsi)
 static void exynos_dsi_enable(struct drm_encoder *encoder)
 {
        struct exynos_dsi *dsi = encoder_to_dsi(encoder);
+       struct drm_bridge *iter;
        int ret;
 
        if (dsi->state & DSIM_STATE_ENABLED)
@@ -1391,7 +1392,11 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
                if (ret < 0)
                        goto err_put_sync;
        } else {
-               drm_bridge_chain_pre_enable(dsi->out_bridge);
+               list_for_each_entry_reverse(iter, &encoder->bridge_chain,
+                                           chain_node) {
+                       if (iter->funcs->pre_enable)
+                               iter->funcs->pre_enable(iter);
+               }
        }
 
        exynos_dsi_set_display_mode(dsi);
@@ -1402,7 +1407,10 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
                if (ret < 0)
                        goto err_display_disable;
        } else {
-               drm_bridge_chain_enable(dsi->out_bridge);
+               list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
+                       if (iter->funcs->enable)
+                               iter->funcs->enable(iter);
+               }
        }
 
        dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
@@ -1420,6 +1428,7 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
 static void exynos_dsi_disable(struct drm_encoder *encoder)
 {
        struct exynos_dsi *dsi = encoder_to_dsi(encoder);
+       struct drm_bridge *iter;
 
        if (!(dsi->state & DSIM_STATE_ENABLED))
                return;
@@ -1427,10 +1436,20 @@ static void exynos_dsi_disable(struct drm_encoder *encoder)
        dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
 
        drm_panel_disable(dsi->panel);
-       drm_bridge_chain_disable(dsi->out_bridge);
+
+       list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
+               if (iter->funcs->disable)
+                       iter->funcs->disable(iter);
+       }
+
        exynos_dsi_set_display_enable(dsi, false);
        drm_panel_unprepare(dsi->panel);
-       drm_bridge_chain_post_disable(dsi->out_bridge);
+
+       list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
+               if (iter->funcs->post_disable)
+                       iter->funcs->post_disable(iter);
+       }
+
        dsi->state &= ~DSIM_STATE_ENABLED;
        pm_runtime_put_sync(dsi->dev);
 }
@@ -1523,7 +1542,7 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
        if (out_bridge) {
                drm_bridge_attach(encoder, out_bridge, NULL);
                dsi->out_bridge = out_bridge;
-               list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
+               list_splice_init(&encoder->bridge_chain, &dsi->bridge_chain);
        } else {
                int ret = exynos_dsi_create_connector(encoder);
 

Re: [PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list

[Boris Brezillon]

On Fri, 27 Dec 2019 14:23:13 +0100
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> On Fri, 27 Dec 2019 13:00:04 +0100
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
> 
> > On Fri, 27 Dec 2019 12:01:35 +0100
> > Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> >   
> > > Exynos DSI DRM driver uses private calls to out bridge to force certain
> > > order of operations during init/exit sequences. This no longer works after
> > > conversion of bridge chain to a double-linked list. To fix the regression
> > > call bridge related operations manually instead of the generic
> > > drm_bridge_chain_*() operations.    
> > 
> > I think it'd be worth explaining what the problem is (infinite loop
> > caused by list_for_each_entry() use when the bridge is no longer part
> > of the chain attached to the encoder).
> >   
> > > 
> > > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > > Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")    
> > 
> > We also need to fix that in VC4.
> >   
> > > ---
> > > This patch is a result of the following discussion:
> > > https://www.spinics.net/lists/dri-devel/msg239256.html
> > > ---
> > >  drivers/gpu/drm/exynos/exynos_drm_dsi.c | 21 ++++++++++++---------
> > >  1 file changed, 12 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > index 3955f84dc893..f5905c239a86 100644
> > > --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > @@ -255,7 +255,6 @@ struct exynos_dsi {
> > >  	struct mipi_dsi_host dsi_host;
> > >  	struct drm_connector connector;
> > >  	struct drm_panel *panel;
> > > -	struct list_head bridge_chain;
> > >  	struct drm_bridge *out_bridge;
> > >  	struct device *dev;
> > >  
> > > @@ -1391,7 +1390,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> > >  		if (ret < 0)
> > >  			goto err_put_sync;
> > >  	} else {
> > > -		drm_bridge_chain_pre_enable(dsi->out_bridge);
> > > +		if (dsi->out_bridge->funcs->pre_enable)
> > > +			dsi->out_bridge->funcs->pre_enable(dsi->out_bridge);    
> > 
> > Okay, so you're calling ->{pre_enable,enable,disable,post_disable}() on
> > the first bridge element which only works if the chain contains one
> > bridge (see below). Maybe you should keep exynos_dsi.bridge_chain and
> > create custom helpers to iterate over chain elements instead of calling
> > those hooks only on out_bridge.  
> 
> The following diff should fix the problem while keeping the solution
> generic enough to support chains containing more than one bridge.
> 
> --->8---  
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index 3955f84dc893..c861b640fc59 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -1378,6 +1378,7 @@ static void exynos_dsi_unregister_te_irq(struct exynos_dsi *dsi)
>  static void exynos_dsi_enable(struct drm_encoder *encoder)
>  {
>         struct exynos_dsi *dsi = encoder_to_dsi(encoder);
> +       struct drm_bridge *iter;
>         int ret;
>  
>         if (dsi->state & DSIM_STATE_ENABLED)
> @@ -1391,7 +1392,11 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>                 if (ret < 0)
>                         goto err_put_sync;
>         } else {
> -               drm_bridge_chain_pre_enable(dsi->out_bridge);
> +               list_for_each_entry_reverse(iter, &encoder->bridge_chain,

						     ^&dsi->bridge_chain

And the same applies to all list_for_each() calls in this patch.

> +                                           chain_node) {
> +                       if (iter->funcs->pre_enable)
> +                               iter->funcs->pre_enable(iter);
> +               }
>         }
>  
>         exynos_dsi_set_display_mode(dsi);
> @@ -1402,7 +1407,10 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>                 if (ret < 0)
>                         goto err_display_disable;
>         } else {
> -               drm_bridge_chain_enable(dsi->out_bridge);
> +               list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
> +                       if (iter->funcs->enable)
> +                               iter->funcs->enable(iter);
> +               }
>         }
>  
>         dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
> @@ -1420,6 +1428,7 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>  static void exynos_dsi_disable(struct drm_encoder *encoder)
>  {
>         struct exynos_dsi *dsi = encoder_to_dsi(encoder);
> +       struct drm_bridge *iter;
>  
>         if (!(dsi->state & DSIM_STATE_ENABLED))
>                 return;
> @@ -1427,10 +1436,20 @@ static void exynos_dsi_disable(struct drm_encoder *encoder)
>         dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>  
>         drm_panel_disable(dsi->panel);
> -       drm_bridge_chain_disable(dsi->out_bridge);
> +
> +       list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> +               if (iter->funcs->disable)
> +                       iter->funcs->disable(iter);
> +       }
> +
>         exynos_dsi_set_display_enable(dsi, false);
>         drm_panel_unprepare(dsi->panel);
> -       drm_bridge_chain_post_disable(dsi->out_bridge);
> +
> +       list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
> +               if (iter->funcs->post_disable)
> +                       iter->funcs->post_disable(iter);
> +       }
> +
>         dsi->state &= ~DSIM_STATE_ENABLED;
>         pm_runtime_put_sync(dsi->dev);
>  }
> @@ -1523,7 +1542,7 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
>         if (out_bridge) {
>                 drm_bridge_attach(encoder, out_bridge, NULL);
>                 dsi->out_bridge = out_bridge;
> -               list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
> +               list_splice_init(&encoder->bridge_chain, &dsi->bridge_chain);
>         } else {
>                 int ret = exynos_dsi_create_connector(encoder);
>