Revert "drm: of: Properly try all possible cases for bridge/panel detection"

Commit '80253168dbfd ("drm: of: Lookup if child node has panel or
bridge")' introduced the ability to describe a panel under a display
controller without having to use a graph to connect the controller to
its single child panel (or bridge).

The implementation of this would find the first non-graph node and
attempt to acquire the related panel or bridge. This prevents cases
where any other child node, such as a aux bus for a DisplayPort
controller, or an opp-table to find the referenced panel.

Commit '67bae5f28c89 ("drm: of: Properly try all possible cases for
bridge/panel detection")' attempted to solve this problem by not
bypassing the graph reference lookup before attempting to find the panel
or bridge.

While this does solve the case where a proper graph reference is
present, it does not allow the caller to distinguish between a
yet-to-be-probed panel or bridge and the absence of a reference to a
panel.

One such case is a DisplayPort controller that on some boards have an
explicitly described reference to a panel, but on others have a
discoverable DisplayPort display attached (which doesn't need to be
expressed in DeviceTree).

This reverts commit '67bae5f28c89 ("drm: of: Properly try all possible
cases for bridge/panel detection")', as a step towards reverting commit
'80253168dbfd ("drm: of: Lookup if child node has panel or bridge")'.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420231230.58499-1-bjorn.andersson@linaro.org

diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
index f4df344509a87245d97f701433a4de41dc702d08..026e4e29a0f374436a839303c019eef0541fb45a 100644 (file)
--- a/drivers/gpu/drm/drm_of.c
+++ b/drivers/gpu/drm/drm_of.c
@@ -214,29 +214,6 @@ int drm_of_encoder_active_endpoint(struct device_node *node,
 }
 EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
 
-static int find_panel_or_bridge(struct device_node *node,
-                               struct drm_panel **panel,
-                               struct drm_bridge **bridge)
-{
-       if (panel) {
-               *panel = of_drm_find_panel(node);
-               if (!IS_ERR(*panel))
-                       return 0;
-
-               /* Clear the panel pointer in case of error. */
-               *panel = NULL;
-       }
-
-       /* No panel found yet, check for a bridge next. */
-       if (bridge) {
-               *bridge = of_drm_find_bridge(node);
-               if (*bridge)
-                       return 0;
-       }
-
-       return -EPROBE_DEFER;
-}
-
 /**
  * drm_of_find_panel_or_bridge - return connected panel or bridge device
  * @np: device tree node containing encoder output ports
@@ -259,44 +236,66 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
                                struct drm_panel **panel,
                                struct drm_bridge **bridge)
 {
-       struct device_node *node;
-       int ret;
+       int ret = -EPROBE_DEFER;
+       struct device_node *remote;
 
        if (!panel && !bridge)
                return -EINVAL;
-
        if (panel)
                *panel = NULL;
-       if (bridge)
-               *bridge = NULL;
-
-       /* Check for a graph on the device node first. */
-       if (of_graph_is_present(np)) {
-               node = of_graph_get_remote_node(np, port, endpoint);
-               if (node) {
-                       ret = find_panel_or_bridge(node, panel, bridge);
-                       of_node_put(node);
-
-                       if (!ret)
-                               return 0;
-               }
-       }
 
-       /* Otherwise check for any child node other than port/ports. */
-       for_each_available_child_of_node(np, node) {
-               if (of_node_name_eq(node, "port") ||
-                   of_node_name_eq(node, "ports"))
+       /**
+        * Devices can also be child nodes when we also control that device
+        * through the upstream device (ie, MIPI-DCS for a MIPI-DSI device).
+        *
+        * Lookup for a child node of the given parent that isn't either port
+        * or ports.
+        */
+       for_each_available_child_of_node(np, remote) {
+               if (of_node_name_eq(remote, "port") ||
+                   of_node_name_eq(remote, "ports"))
                        continue;
 
-               ret = find_panel_or_bridge(node, panel, bridge);
-               of_node_put(node);
+               goto of_find_panel_or_bridge;
+       }
+
+       /*
+        * of_graph_get_remote_node() produces a noisy error message if port
+        * node isn't found and the absence of the port is a legit case here,
+        * so at first we silently check whether graph presents in the
+        * device-tree node.
+        */
+       if (!of_graph_is_present(np))
+               return -ENODEV;
+
+       remote = of_graph_get_remote_node(np, port, endpoint);
+
+of_find_panel_or_bridge:
+       if (!remote)
+               return -ENODEV;
+
+       if (panel) {
+               *panel = of_drm_find_panel(remote);
+               if (!IS_ERR(*panel))
+                       ret = 0;
+               else
+                       *panel = NULL;
+       }
+
+       /* No panel found yet, check for a bridge next. */
+       if (bridge) {
+               if (ret) {
+                       *bridge = of_drm_find_bridge(remote);
+                       if (*bridge)
+                               ret = 0;
+               } else {
+                       *bridge = NULL;
+               }
 
-               /* Stop at the first found occurrence. */
-               if (!ret)
-                       return 0;
        }
 
-       return -EPROBE_DEFER;
+       of_node_put(remote);
+       return ret;
 }
 EXPORT_SYMBOL_GPL(drm_of_find_panel_or_bridge);