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From:   Paul Kocialkowski <paul.kocialkowski@bootlin.com>
To:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Linus Walleij <linus.walleij@linaro.org>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Subject: [PATCH v3] drm: of: Properly try all possible cases for bridge/panel detection
Date:   Tue, 29 Mar 2022 15:27:32 +0200
Message-Id: <20220329132732.628474-1-paul.kocialkowski@bootlin.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

While bridge/panel detection was initially relying on the usual
port/ports-based of graph detection, it was recently changed to
perform the lookup on any child node that is not port/ports
instead when such a node is available, with no fallback on the
usual way.

This results in breaking detection when a child node is present
but does not contain any panel or bridge node, even when the
usual port/ports-based of graph is there.

In order to support both situations properly, this commit reworks
the logic to try both options and not just one of the two: it will
only return -EPROBE_DEFER when both have failed.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Fixes: 80253168dbfd ("drm: of: Lookup if child node has panel or bridge")
---

Changes since v2:
- Removed unnecessary else statement and added a comment about
  clearing the panel pointer on error.

Changes since v1:
- Renamed remote to node;
- Renamed helper to find_panel_or_bridge;
- Cleared bridge pointer early;
- Returned early to make the code more concise;

---
 drivers/gpu/drm/drm_of.c | 99 ++++++++++++++++++++--------------------
 1 file changed, 50 insertions(+), 49 deletions(-)

diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
index 9d90cd75c457..8716da6369a6 100644
--- a/drivers/gpu/drm/drm_of.c
+++ b/drivers/gpu/drm/drm_of.c
@@ -219,6 +219,29 @@ 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
@@ -241,66 +264,44 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 				struct drm_panel **panel,
 				struct drm_bridge **bridge)
 {
-	int ret = -EPROBE_DEFER;
-	struct device_node *remote;
+	struct device_node *node;
+	int ret;
 
 	if (!panel && !bridge)
 		return -EINVAL;
+
 	if (panel)
 		*panel = NULL;
-
-	/**
-	 * 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;
-
-		goto of_find_panel_or_bridge;
+	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;
+		}
 	}
 
-	/*
-	 * 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;
+	/* 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"))
+			continue;
 
-	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;
-		}
+		ret = find_panel_or_bridge(node, panel, bridge);
+		of_node_put(node);
 
+		/* Stop at the first found occurrence. */
+		if (!ret)
+			return 0;
 	}
 
-	of_node_put(remote);
-	return ret;
+	return -EPROBE_DEFER;
 }
 EXPORT_SYMBOL_GPL(drm_of_find_panel_or_bridge);
 
-- 
2.35.1