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.brezil...@collabora.com>
Reviewed-by: Neil Armstrong <narmstr...@baylibre.com>
Reviewed-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
---
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;
 };
-- 
2.23.0

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