Re: [PATCH v4 04/11] drm/bridge: Make the bridge chain a double-linked list

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Hi All,

On 03.12.2019 15:15, Boris Brezillon wrote:
> So that each element in the chain can easily access its predecessor.
> This will be needed to support bus format negotiation between elements
> of the bridge chain.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Reviewed-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

I've noticed that this patch got merged to linux-next as commit 
05193dc38197021894b17239fafbd2eb1afe5a45. Sadly it breaks booting of 
Samsung Exynos5250-based Arndale board. Booting stops after following 
messages:

[drm] Exynos DRM: using 14400000.fimd device for DMA mapping operations
exynos-drm exynos-drm: bound 14400000.fimd (ops fimd_component_ops)
exynos-drm exynos-drm: bound 14450000.mixer (ops mixer_component_ops)
exynos-drm exynos-drm: bound 14500000.dsi (ops exynos_dsi_component_ops)
exynos-drm exynos-drm: bound 14530000.hdmi (ops hdmi_component_ops)
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] No driver support for vblank timestamp query.
[drm] Cannot find any crtc or sizes
[drm] Cannot find any crtc or sizes
[drm] Initialized exynos 1.1.0 20180330 for exynos-drm on minor 0

I will try to debug this and provide more information soon.

> ---
> Changes in v4:
> * Simplify the drm_bridge_attach() logic
> * Fix list iteration bugs
> * Patch VC4 and Exynos DSI drivers to match core changes
> * Add R-bs
>
> Changes in v3:
> * None
>
> Changes in v2:
> * Adjust things to the "dummy encoder bridge" change (patch 2 in this
>    series)
> ---
>   drivers/gpu/drm/drm_bridge.c            | 171 +++++++++++++++---------
>   drivers/gpu/drm/drm_encoder.c           |  16 +--
>   drivers/gpu/drm/exynos/exynos_drm_dsi.c |   5 +-
>   drivers/gpu/drm/vc4/vc4_dsi.c           |  10 +-
>   include/drm/drm_bridge.h                |  12 +-
>   include/drm/drm_encoder.h               |   7 +-
>   6 files changed, 143 insertions(+), 78 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 54c874493c57..b6517b4fa3d1 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -55,7 +55,7 @@
>    * just provide additional hooks to get the desired output at the end of the
>    * encoder chain.
>    *
> - * Bridges can also be chained up using the &drm_bridge.next pointer.
> + * Bridges can also be chained up using the &drm_bridge.chain_node field.
>    *
>    * Both legacy CRTC helpers and the new atomic modeset helpers support bridges.
>    */
> @@ -128,20 +128,21 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>   	bridge->dev = encoder->dev;
>   	bridge->encoder = encoder;
>   
> +	if (previous)
> +		list_add(&bridge->chain_node, &previous->chain_node);
> +	else
> +		list_add(&bridge->chain_node, &encoder->bridge_chain);
> +
>   	if (bridge->funcs->attach) {
>   		ret = bridge->funcs->attach(bridge);
>   		if (ret < 0) {
> +			list_del(&bridge->chain_node);
>   			bridge->dev = NULL;
>   			bridge->encoder = NULL;
>   			return ret;
>   		}
>   	}
>   
> -	if (previous)
> -		previous->next = bridge;
> -	else
> -		encoder->bridge = bridge;
> -
>   	return 0;
>   }
>   EXPORT_SYMBOL(drm_bridge_attach);
> @@ -157,6 +158,7 @@ void drm_bridge_detach(struct drm_bridge *bridge)
>   	if (bridge->funcs->detach)
>   		bridge->funcs->detach(bridge);
>   
> +	list_del(&bridge->chain_node);
>   	bridge->dev = NULL;
>   }
>   
> @@ -190,18 +192,21 @@ bool drm_bridge_chain_mode_fixup(struct drm_bridge *bridge,
>   				 const struct drm_display_mode *mode,
>   				 struct drm_display_mode *adjusted_mode)
>   {
> -	bool ret = true;
> +	struct drm_encoder *encoder;
>   
>   	if (!bridge)
>   		return true;
>   
> -	if (bridge->funcs->mode_fixup)
> -		ret = bridge->funcs->mode_fixup(bridge, mode, adjusted_mode);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (!bridge->funcs->mode_fixup)
> +			continue;
>   
> -	ret = ret && drm_bridge_chain_mode_fixup(bridge->next, mode,
> -						 adjusted_mode);
> +		if (!bridge->funcs->mode_fixup(bridge, mode, adjusted_mode))
> +			return false;
> +	}
>   
> -	return ret;
> +	return true;
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_mode_fixup);
>   
> @@ -224,18 +229,24 @@ enum drm_mode_status
>   drm_bridge_chain_mode_valid(struct drm_bridge *bridge,
>   			    const struct drm_display_mode *mode)
>   {
> -	enum drm_mode_status ret = MODE_OK;
> +	struct drm_encoder *encoder;
>   
>   	if (!bridge)
> -		return ret;
> +		return MODE_OK;
>   
> -	if (bridge->funcs->mode_valid)
> -		ret = bridge->funcs->mode_valid(bridge, mode);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		enum drm_mode_status ret;
> +
> +		if (!bridge->funcs->mode_valid)
> +			continue;
>   
> -	if (ret != MODE_OK)
> -		return ret;
> +		ret = bridge->funcs->mode_valid(bridge, mode);
> +		if (ret != MODE_OK)
> +			return ret;
> +	}
>   
> -	return drm_bridge_chain_mode_valid(bridge->next, mode);
> +	return MODE_OK;
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_mode_valid);
>   
> @@ -251,13 +262,20 @@ EXPORT_SYMBOL(drm_bridge_chain_mode_valid);
>    */
>   void drm_bridge_chain_disable(struct drm_bridge *bridge)
>   {
> +	struct drm_encoder *encoder;
> +	struct drm_bridge *iter;
> +
>   	if (!bridge)
>   		return;
>   
> -	drm_bridge_chain_disable(bridge->next);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> +		if (iter->funcs->disable)
> +			iter->funcs->disable(iter);
>   
> -	if (bridge->funcs->disable)
> -		bridge->funcs->disable(bridge);
> +		if (iter == bridge)
> +			break;
> +	}
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_disable);
>   
> @@ -274,13 +292,16 @@ EXPORT_SYMBOL(drm_bridge_chain_disable);
>    */
>   void drm_bridge_chain_post_disable(struct drm_bridge *bridge)
>   {
> +	struct drm_encoder *encoder;
> +
>   	if (!bridge)
>   		return;
>   
> -	if (bridge->funcs->post_disable)
> -		bridge->funcs->post_disable(bridge);
> -
> -	drm_bridge_chain_post_disable(bridge->next);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (bridge->funcs->post_disable)
> +			bridge->funcs->post_disable(bridge);
> +	}
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_post_disable);
>   
> @@ -300,13 +321,16 @@ void drm_bridge_chain_mode_set(struct drm_bridge *bridge,
>   			       const struct drm_display_mode *mode,
>   			       const struct drm_display_mode *adjusted_mode)
>   {
> +	struct drm_encoder *encoder;
> +
>   	if (!bridge)
>   		return;
>   
> -	if (bridge->funcs->mode_set)
> -		bridge->funcs->mode_set(bridge, mode, adjusted_mode);
> -
> -	drm_bridge_chain_mode_set(bridge->next, mode, adjusted_mode);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (bridge->funcs->mode_set)
> +			bridge->funcs->mode_set(bridge, mode, adjusted_mode);
> +	}
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_mode_set);
>   
> @@ -323,13 +347,17 @@ EXPORT_SYMBOL(drm_bridge_chain_mode_set);
>    */
>   void drm_bridge_chain_pre_enable(struct drm_bridge *bridge)
>   {
> +	struct drm_encoder *encoder;
> +	struct drm_bridge *iter;
> +
>   	if (!bridge)
>   		return;
>   
> -	drm_bridge_chain_pre_enable(bridge->next);
> -
> -	if (bridge->funcs->pre_enable)
> -		bridge->funcs->pre_enable(bridge);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> +		if (iter->funcs->pre_enable)
> +			iter->funcs->pre_enable(iter);
> +	}
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_pre_enable);
>   
> @@ -345,13 +373,16 @@ EXPORT_SYMBOL(drm_bridge_chain_pre_enable);
>    */
>   void drm_bridge_chain_enable(struct drm_bridge *bridge)
>   {
> +	struct drm_encoder *encoder;
> +
>   	if (!bridge)
>   		return;
>   
> -	if (bridge->funcs->enable)
> -		bridge->funcs->enable(bridge);
> -
> -	drm_bridge_chain_enable(bridge->next);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (bridge->funcs->enable)
> +			bridge->funcs->enable(bridge);
> +	}
>   }
>   EXPORT_SYMBOL(drm_bridge_chain_enable);
>   
> @@ -370,15 +401,22 @@ EXPORT_SYMBOL(drm_bridge_chain_enable);
>   void drm_atomic_bridge_chain_disable(struct drm_bridge *bridge,
>   				     struct drm_atomic_state *state)
>   {
> +	struct drm_encoder *encoder;
> +	struct drm_bridge *iter;
> +
>   	if (!bridge)
>   		return;
>   
> -	drm_atomic_bridge_chain_disable(bridge->next, state);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> +		if (iter->funcs->atomic_disable)
> +			iter->funcs->atomic_disable(iter, state);
> +		else if (iter->funcs->disable)
> +			iter->funcs->disable(iter);
>   
> -	if (bridge->funcs->atomic_disable)
> -		bridge->funcs->atomic_disable(bridge, state);
> -	else if (bridge->funcs->disable)
> -		bridge->funcs->disable(bridge);
> +		if (iter == bridge)
> +			break;
> +	}
>   }
>   EXPORT_SYMBOL(drm_atomic_bridge_chain_disable);
>   
> @@ -398,15 +436,18 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_disable);
>   void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge,
>   					  struct drm_atomic_state *state)
>   {
> +	struct drm_encoder *encoder;
> +
>   	if (!bridge)
>   		return;
>   
> -	if (bridge->funcs->atomic_post_disable)
> -		bridge->funcs->atomic_post_disable(bridge, state);
> -	else if (bridge->funcs->post_disable)
> -		bridge->funcs->post_disable(bridge);
> -
> -	drm_atomic_bridge_chain_post_disable(bridge->next, state);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (bridge->funcs->atomic_post_disable)
> +			bridge->funcs->atomic_post_disable(bridge, state);
> +		else if (bridge->funcs->post_disable)
> +			bridge->funcs->post_disable(bridge);
> +	}
>   }
>   EXPORT_SYMBOL(drm_atomic_bridge_chain_post_disable);
>   
> @@ -426,15 +467,22 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_post_disable);
>   void drm_atomic_bridge_chain_pre_enable(struct drm_bridge *bridge,
>   					struct drm_atomic_state *state)
>   {
> +	struct drm_encoder *encoder;
> +	struct drm_bridge *iter;
> +
>   	if (!bridge)
>   		return;
>   
> -	drm_atomic_bridge_chain_pre_enable(bridge->next, state);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> +		if (iter->funcs->atomic_pre_enable)
> +			iter->funcs->atomic_pre_enable(iter, state);
> +		else if (iter->funcs->pre_enable)
> +			iter->funcs->pre_enable(iter);
>   
> -	if (bridge->funcs->atomic_pre_enable)
> -		bridge->funcs->atomic_pre_enable(bridge, state);
> -	else if (bridge->funcs->pre_enable)
> -		bridge->funcs->pre_enable(bridge);
> +		if (iter == bridge)
> +			break;
> +	}
>   }
>   EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable);
>   
> @@ -453,15 +501,18 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable);
>   void drm_atomic_bridge_chain_enable(struct drm_bridge *bridge,
>   				    struct drm_atomic_state *state)
>   {
> +	struct drm_encoder *encoder;
> +
>   	if (!bridge)
>   		return;
>   
> -	if (bridge->funcs->atomic_enable)
> -		bridge->funcs->atomic_enable(bridge, state);
> -	else if (bridge->funcs->enable)
> -		bridge->funcs->enable(bridge);
> -
> -	drm_atomic_bridge_chain_enable(bridge->next, state);
> +	encoder = bridge->encoder;
> +	list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
> +		if (bridge->funcs->atomic_enable)
> +			bridge->funcs->atomic_enable(bridge, state);
> +		else if (bridge->funcs->enable)
> +			bridge->funcs->enable(bridge);
> +	}
>   }
>   EXPORT_SYMBOL(drm_atomic_bridge_chain_enable);
>   
> diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c
> index a2cc7e7241a9..e555281f43d4 100644
> --- a/drivers/gpu/drm/drm_encoder.c
> +++ b/drivers/gpu/drm/drm_encoder.c
> @@ -140,6 +140,7 @@ int drm_encoder_init(struct drm_device *dev,
>   		goto out_put;
>   	}
>   
> +	INIT_LIST_HEAD(&encoder->bridge_chain);
>   	list_add_tail(&encoder->head, &dev->mode_config.encoder_list);
>   	encoder->index = dev->mode_config.num_encoder++;
>   
> @@ -160,23 +161,16 @@ EXPORT_SYMBOL(drm_encoder_init);
>   void drm_encoder_cleanup(struct drm_encoder *encoder)
>   {
>   	struct drm_device *dev = encoder->dev;
> +	struct drm_bridge *bridge, *next;
>   
>   	/* Note that the encoder_list is considered to be static; should we
>   	 * remove the drm_encoder at runtime we would have to decrement all
>   	 * the indices on the drm_encoder after us in the encoder_list.
>   	 */
>   
> -	if (encoder->bridge) {
> -		struct drm_bridge *bridge;
> -		struct drm_bridge *next;
> -
> -		bridge = drm_bridge_chain_get_first_bridge(encoder);
> -		while (bridge) {
> -			next = drm_bridge_get_next_bridge(bridge);
> -			drm_bridge_detach(bridge);
> -			bridge = next;
> -		}
> -	}
> +	list_for_each_entry_safe(bridge, next, &encoder->bridge_chain,
> +				 chain_node)
> +		drm_bridge_detach(bridge);
>   
>   	drm_mode_object_unregister(dev, &encoder->base);
>   	kfree(encoder->name);
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index d984097704b8..7de82e22252a 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -255,6 +255,7 @@ 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;
>   
> @@ -1522,7 +1523,7 @@ 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;
> -		encoder->bridge = NULL;
> +		list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
>   	} else {
>   		int ret = exynos_dsi_create_connector(encoder);
>   
> @@ -1588,6 +1589,7 @@ 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)
> @@ -1735,6 +1737,7 @@ 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;
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index ff81b54ea281..6c5b80ad6154 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -499,6 +499,7 @@ struct vc4_dsi {
>   	struct mipi_dsi_host dsi_host;
>   	struct drm_encoder *encoder;
>   	struct drm_bridge *bridge;
> +	struct list_head bridge_chain;
>   
>   	void __iomem *regs;
>   
> @@ -1460,6 +1461,8 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
>   				       GFP_KERNEL);
>   	if (!vc4_dsi_encoder)
>   		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&dsi->bridge_chain);
>   	vc4_dsi_encoder->base.type = VC4_ENCODER_TYPE_DSI1;
>   	vc4_dsi_encoder->dsi = dsi;
>   	dsi->encoder = &vc4_dsi_encoder->base.base;
> @@ -1610,7 +1613,7 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
>   	 * from our driver, since we need to sequence them within the
>   	 * encoder's enable/disable paths.
>   	 */
> -	dsi->encoder->bridge = NULL;
> +	list_splice(&dsi->encoder->bridge_chain, &dsi->bridge_chain);
>   
>   	if (dsi->port == 0)
>   		vc4_debugfs_add_regset32(drm, "dsi0_regs", &dsi->regset);
> @@ -1632,6 +1635,11 @@ static void vc4_dsi_unbind(struct device *dev, struct device *master,
>   	if (dsi->bridge)
>   		pm_runtime_disable(dev);
>   
> +	/*
> +	 * Restore the bridge_chain so the bridge detach procedure can happen
> +	 * normally.
> +	 */
> +	list_splice(&dsi->bridge_chain, &dsi->encoder->bridge_chain);
>   	vc4_dsi_encoder_destroy(dsi->encoder);
>   
>   	if (dsi->port == 1)
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index bd78c256b1ed..c118726469ee 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -384,8 +384,8 @@ struct drm_bridge {
>   	struct drm_device *dev;
>   	/** @encoder: encoder to which this bridge is connected */
>   	struct drm_encoder *encoder;
> -	/** @next: the next bridge in the encoder chain */
> -	struct drm_bridge *next;
> +	/** @chain_node: used to form a bridge chain */
> +	struct list_head chain_node;
>   #ifdef CONFIG_OF
>   	/** @of_node: device node pointer to the bridge */
>   	struct device_node *of_node;
> @@ -420,7 +420,10 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>   static inline struct drm_bridge *
>   drm_bridge_get_next_bridge(struct drm_bridge *bridge)
>   {
> -	return bridge->next;
> +	if (list_is_last(&bridge->chain_node, &bridge->encoder->bridge_chain))
> +		return NULL;
> +
> +	return list_next_entry(bridge, chain_node);
>   }
>   
>   /**
> @@ -434,7 +437,8 @@ drm_bridge_get_next_bridge(struct drm_bridge *bridge)
>   static inline struct drm_bridge *
>   drm_bridge_chain_get_first_bridge(struct drm_encoder *encoder)
>   {
> -	return encoder->bridge;
> +	return list_first_entry_or_null(&encoder->bridge_chain,
> +					struct drm_bridge, chain_node);
>   }
>   
>   bool drm_bridge_chain_mode_fixup(struct drm_bridge *bridge,
> diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h
> index f06164f44efe..5623994b6e9e 100644
> --- a/include/drm/drm_encoder.h
> +++ b/include/drm/drm_encoder.h
> @@ -172,7 +172,12 @@ struct drm_encoder {
>   	 * &drm_connector_state.crtc.
>   	 */
>   	struct drm_crtc *crtc;
> -	struct drm_bridge *bridge;
> +
> +	/**
> +	 * @bridge_chain: Bridges attached to this encoder.
> +	 */
> +	struct list_head bridge_chain;
> +
>   	const struct drm_encoder_funcs *funcs;
>   	const struct drm_encoder_helper_funcs *helper_private;
>   };

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland




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