[PATCH 05/11] drm/bridge: panel: add a panel_bridge to every panel

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Adding a panel does currently not add a panel_bridge wrapping it. Usually
the panel_bridge creation happens later, when some other driver (e.g. the
previous bridge or the encoder) calls *_of_get_bridge() and the following
element in the pipeline is a panel.

This has some drawbacks:

 * hte bridge API is currently the best practice to access various
   components of the pipeline, especially with complex cards where bridges
   can be combined in different ways on different hardware
 * the panel_bridge is not created in the context of the driver of the
   underlying physical device (the panel driver), but of some other driver
 * that other driver is not aware of whether the returned drm_bridge
   pointer is a panel_bridge created on the fly, a pre-existing
   panel_bridge or a non-panel bridge
 * removal of a panel_bridge requires calling drm_panel_bridge_remove(),
   but the other driver doesn't know whether this is needed because it
   doesn't know whether it has created a panel_bridge or not

So far the current approach has been working because devm and drmm ensure
the panel bridge would be dealloacted at some later point. However with the
upcoming implementation of dynamic bridge lifetime this will get more
complicated.

Switch to the new approach: always create a panel_bridge with a drm_panel,
thus matching the lifetime of the drm_panel and the panel_bridge wrapping
it. This makes lifetime much more straightforward to understand and to
further develop on.

As a consequence devm_drm_of_get_bridge() and drmm_of_get_bridge() don't
need to look for a panel anymore and become simple wrappers to
of_drm_get_bridge_by_endpoint(). Also deprecate them as they can be
replaced by of_drm_get_bridge_by_endpoint() which also handles refcount.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
 drivers/gpu/drm/bridge/panel.c | 47 +++++++++++++++++++++---------------------
 drivers/gpu/drm/drm_panel.c    |  3 +++
 include/drm/drm_panel.h        |  8 +++++++
 3 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
index 02388a3de626..d86555254aa9 100644
--- a/drivers/gpu/drm/bridge/panel.c
+++ b/drivers/gpu/drm/bridge/panel.c
@@ -412,6 +412,11 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
 {
 	struct drm_bridge **ptr, *bridge;
 
+	if (panel->bridge) {
+		dev_dbg(dev, "returning existing bridge=%p\n", panel->bridge);
+		return panel->bridge;
+	}
+
 	ptr = devres_alloc(devm_drm_panel_bridge_release, sizeof(*ptr),
 			   GFP_KERNEL);
 	if (!ptr)
@@ -495,9 +500,12 @@ EXPORT_SYMBOL(drm_panel_bridge_connector);
  * @port: port in the device tree node
  * @endpoint: endpoint in the device tree node
  *
+ * This function is deprecated and should not be used in new drivers. The
+ * returned bridge refcount is not incremented! Replace by
+ * of_drm_get_bridge_by_endpoint() and handle bridge refcount.
+ *
  * Given a DT node's port and endpoint number, finds the connected node
- * and returns the associated bridge if any, or creates and returns a
- * drm panel bridge instance if a panel is connected.
+ * and returns the associated bridge if any.
  *
  * Returns a pointer to the bridge if successful, or an error pointer
  * otherwise.
@@ -507,18 +515,12 @@ struct drm_bridge *devm_drm_of_get_bridge(struct device *dev,
 					  u32 port, u32 endpoint)
 {
 	struct drm_bridge *bridge;
-	struct drm_panel *panel;
-	int ret;
 
-	ret = drm_of_find_panel_or_bridge(np, port, endpoint,
-					  &panel, &bridge);
-	if (ret)
-		return ERR_PTR(ret);
+	bridge = of_drm_get_bridge_by_endpoint(np, port, endpoint);
+	if (IS_ERR(bridge))
+		return bridge;
 
-	if (panel) {
-		bridge = devm_drm_panel_bridge_add(dev, panel);
-		drm_panel_put(panel);
-	}
+	drm_bridge_put(bridge);
 
 	return bridge;
 }
@@ -531,9 +533,12 @@ EXPORT_SYMBOL(devm_drm_of_get_bridge);
  * @port: port in the device tree node
  * @endpoint: endpoint in the device tree node
  *
+ * This function is deprecated and should not be used in new drivers. The
+ * returned bridge refcount is not incremented! Replace by
+ * of_drm_get_bridge_by_endpoint() and handle bridge refcount.
+ *
  * Given a DT node's port and endpoint number, finds the connected node
- * and returns the associated bridge if any, or creates and returns a
- * drm panel bridge instance if a panel is connected.
+ * and returns the associated bridge if any.
  *
  * Returns a drmm managed pointer to the bridge if successful, or an error
  * pointer otherwise.
@@ -543,18 +548,12 @@ struct drm_bridge *drmm_of_get_bridge(struct drm_device *drm,
 				      u32 port, u32 endpoint)
 {
 	struct drm_bridge *bridge;
-	struct drm_panel *panel;
-	int ret;
 
-	ret = drm_of_find_panel_or_bridge(np, port, endpoint,
-					  &panel, &bridge);
-	if (ret)
-		return ERR_PTR(ret);
+	bridge = of_drm_get_bridge_by_endpoint(np, port, endpoint);
+	if (IS_ERR(bridge))
+		return bridge;
 
-	if (panel) {
-		bridge = drmm_panel_bridge_add(drm, panel);
-		drm_panel_put(panel);
-	}
+	drm_bridge_put(bridge);
 
 	return bridge;
 }
diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f8f6082e637f..95fc95d1b4b7 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -453,6 +453,9 @@ void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
 
 	drm_panel_init(panel, dev, funcs, connector_type);
 
+	panel->bridge = devm_drm_panel_bridge_add(dev, panel);
+	WARN_ON(!panel->bridge);
+
 	return container;
 }
 EXPORT_SYMBOL(__devm_drm_panel_alloc);
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index b87323443f49..9a042675eb3e 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -210,6 +210,14 @@ struct drm_panel {
 	 */
 	struct device *dev;
 
+	/**
+	 * @bridge:
+	 *
+	 * Pointer to the panel bridge giving access to the panel using the
+	 * DRM bridge API.
+	 */
+	struct drm_bridge *bridge;
+
 	/**
 	 * @backlight:
 	 *

-- 
2.55.0