drm/bridge: prevent encoder chain changes while iterating with list_for_each_entry_from()

These loops in drm_bridge.c iterate over the encoder chain using
list_for_each_entry_from(), which does not prevent changes to the bridge
chain while iterating over it.

Convert most of those loops to instead use
drm_for_each_bridge_in_chain_from(), which locks the chain.

This also simplifies code.

All the "simple" loops are converted here. The only ones not touched are
those in drm_atomic_bridge_chain_pre_enable() and
drm_atomic_bridge_chain_post_disable(), because they have nested loops
which are not well handled by drm_for_each_bridge_in_chain_from(). Those
two functions are handled by a separate commit.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://patch.msgid.link/20260324-drm-bridge-alloc-encoder-chain-mutex-v5-5-8bf786c5c7e6@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index fed8f1f06d949d66558da2131255ae27c89d5cde..344b7f317bf4df78763290499f3b478ca4a09b04 100644 (file)
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -725,7 +725,7 @@ void drm_bridge_detach(struct drm_bridge *bridge)
 /**
  * drm_bridge_chain_mode_valid - validate the mode against all bridges in the
  *                              encoder chain.
- * @bridge: bridge control structure
+ * @first_bridge: bridge control structure
  * @info: display info against which the mode shall be validated
  * @mode: desired mode to be validated
  *
@@ -739,17 +739,14 @@ void drm_bridge_detach(struct drm_bridge *bridge)
  * MODE_OK on success, drm_mode_status Enum error code on failure
  */
 enum drm_mode_status
-drm_bridge_chain_mode_valid(struct drm_bridge *bridge,
+drm_bridge_chain_mode_valid(struct drm_bridge *first_bridge,
                            const struct drm_display_info *info,
                            const struct drm_display_mode *mode)
 {
-       struct drm_encoder *encoder;
-
-       if (!bridge)
+       if (!first_bridge)
                return MODE_OK;
 
-       encoder = bridge->encoder;
-       list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
+       drm_for_each_bridge_in_chain_from(first_bridge, bridge) {
                enum drm_mode_status ret;
 
                if (!bridge->funcs->mode_valid)
@@ -767,7 +764,7 @@ EXPORT_SYMBOL(drm_bridge_chain_mode_valid);
 /**
  * drm_bridge_chain_mode_set - set proposed mode for all bridges in the
  *                            encoder chain
- * @bridge: bridge control structure
+ * @first_bridge: bridge control structure
  * @mode: desired mode to be set for the encoder chain
  * @adjusted_mode: updated mode that works for this encoder chain
  *
@@ -776,20 +773,16 @@ EXPORT_SYMBOL(drm_bridge_chain_mode_valid);
  *
  * Note: the bridge passed should be the one closest to the encoder
  */
-void drm_bridge_chain_mode_set(struct drm_bridge *bridge,
+void drm_bridge_chain_mode_set(struct drm_bridge *first_bridge,
                               const struct drm_display_mode *mode,
                               const struct drm_display_mode *adjusted_mode)
 {
-       struct drm_encoder *encoder;
-
-       if (!bridge)
+       if (!first_bridge)
                return;
 
-       encoder = bridge->encoder;
-       list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
+       drm_for_each_bridge_in_chain_from(first_bridge, bridge)
                if (bridge->funcs->mode_set)
                        bridge->funcs->mode_set(bridge, mode, adjusted_mode);
-       }
 }
 EXPORT_SYMBOL(drm_bridge_chain_mode_set);
 
@@ -1013,7 +1006,7 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable);
 
 /**
  * drm_atomic_bridge_chain_enable - enables all bridges in the encoder chain
- * @bridge: bridge control structure
+ * @first_bridge: bridge control structure
  * @state: atomic state being committed
  *
  * Calls &drm_bridge_funcs.atomic_enable (falls back on
@@ -1023,22 +1016,18 @@ EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable);
  *
  * Note: the bridge passed should be the one closest to the encoder
  */
-void drm_atomic_bridge_chain_enable(struct drm_bridge *bridge,
+void drm_atomic_bridge_chain_enable(struct drm_bridge *first_bridge,
                                    struct drm_atomic_state *state)
 {
-       struct drm_encoder *encoder;
-
-       if (!bridge)
+       if (!first_bridge)
                return;
 
-       encoder = bridge->encoder;
-       list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) {
+       drm_for_each_bridge_in_chain_from(first_bridge, bridge)
                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);