[PATCH RFC v2 05/19] drm/panel: embed a drm_bridge into every drm_panel

[Luca Ceresoli]

Adding a drm_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:

 * the 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 that other driver doesn't know whether this is needed because it
   doesn't know whether it has created a panel_bridge or not

Other drivers call [a variant of] drm_panel_bridge_add(), which also has
some of the above drawbacks.

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

Switch to the new approach: embed a drm_bridge inside every drm_panel,
which behaves just like the current drm_panel_bridge.

Do this by copying and adapting the code from bridge/panel.c, using
function names that are more suitable within drm_panel.c and doing the
minimal adaptation needed.

Currently drm_bridge and drm_panel have independent refcounted
allocation. As they now become a single struct, just change
drm_panel_get/put() to get/put the bridge. As a result, the refcount for a
drm_bridge embedded in a drm_panel is:

  bridge.refcount == number of drm_bridge_get() calls
                   + number of drm_panel_get() calls
                   - number of drm_bridge_put() calls
                   - number of drm_panel_put() calls

Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>

---

This patch is new in v2, and replaces "drm/bridge: panel: add a
panel_bridge to every panel" which was based on a different approach.
---
 drivers/gpu/drm/drm_panel.c | 258 +++++++++++++++++++++++++++++++++++++++++---
 include/drm/drm_panel.h     |  33 ++++--
 2 files changed, 266 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
index f8f6082e637f..9b86195f9f66 100644
--- a/drivers/gpu/drm/drm_panel.c
+++ b/drivers/gpu/drm/drm_panel.c
@@ -22,15 +22,19 @@
  */
 
 #include <linux/backlight.h>
+#include <linux/debugfs.h>
 #include <linux/err.h>
 #include <linux/export.h>
 #include <linux/module.h>
 #include <linux/of.h>
 
+#include <drm/drm_atomic_helper.h>
 #include <drm/drm_crtc.h>
+#include <drm/drm_modeset_helper_vtables.h>
 #include <drm/drm_of.h>
 #include <drm/drm_panel.h>
 #include <drm/drm_print.h>
+#include <drm/drm_probe_helper.h>
 
 static DEFINE_MUTEX(panel_lock);
 static LIST_HEAD(panel_list);
@@ -46,6 +50,18 @@ static LIST_HEAD(panel_list);
  * take look at drm_panel_bridge_add() and devm_drm_panel_bridge_add().
  */
 
+static inline struct drm_panel *
+drm_bridge_to_panel(const struct drm_bridge *bridge)
+{
+	return container_of(bridge, struct drm_panel, bridge);
+}
+
+static inline struct drm_panel *
+drm_connector_to_panel(const struct drm_connector *connector)
+{
+	return container_of(connector, struct drm_panel, connector);
+}
+
 /**
  * drm_panel_init - initialize a panel
  * @panel: DRM panel
@@ -86,6 +102,7 @@ void drm_panel_add(struct drm_panel *panel)
 	mutex_lock(&panel_lock);
 	list_add_tail(&panel->list, &panel_list);
 	mutex_unlock(&panel_lock);
+	drm_bridge_add(&panel->bridge);
 }
 EXPORT_SYMBOL(drm_panel_add);
 
@@ -97,6 +114,7 @@ EXPORT_SYMBOL(drm_panel_add);
  */
 void drm_panel_remove(struct drm_panel *panel)
 {
+	drm_bridge_remove(&panel->bridge);
 	mutex_lock(&panel_lock);
 	list_del_init(&panel->list);
 	mutex_unlock(&panel_lock);
@@ -370,13 +388,198 @@ int drm_panel_get_modes(struct drm_panel *panel,
 }
 EXPORT_SYMBOL(drm_panel_get_modes);
 
-static void __drm_panel_free(struct kref *kref)
+static int drm_panel_bridge_connector_get_modes(struct drm_connector *connector)
+{
+	struct drm_panel *drm_panel = drm_connector_to_panel(connector);
+
+	return drm_panel_get_modes(drm_panel, connector);
+}
+
+/**
+ * drm_bridge_set_connector_orientation - Set the connector panel
+ * orientation from the bridge that can be transformed to drm_panel.
+ *
+ * @bridge: The drm_bridge for a drm_panel.
+ * @connector: The connector to be set panel orientation.
+ *
+ * Returns 0 on success, negative errno on failure.
+ */
+int drm_bridge_set_connector_orientation(const struct drm_bridge *bridge,
+					 struct drm_connector *connector)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+
+	return drm_connector_set_orientation_from_panel(connector, panel);
+}
+EXPORT_SYMBOL(drm_bridge_set_connector_orientation);
+
+static const struct drm_connector_helper_funcs
+drm_panel_bridge_connector_helper_funcs = {
+	.get_modes = drm_panel_bridge_connector_get_modes,
+};
+
+static const struct drm_connector_funcs drm_panel_bridge_connector_funcs = {
+	.reset = drm_atomic_helper_connector_reset,
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = drm_connector_cleanup,
+	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+};
+
+static int drm_panel_bridge_attach(struct drm_bridge *bridge,
+				   struct drm_encoder *encoder,
+				   enum drm_bridge_attach_flags flags)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_connector *connector = &panel->connector;
+	int ret;
+
+	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
+		return 0;
+
+	drm_connector_helper_add(connector,
+				 &drm_panel_bridge_connector_helper_funcs);
+
+	ret = drm_connector_init(bridge->dev, connector,
+				 &drm_panel_bridge_connector_funcs,
+				 panel->connector_type);
+	if (ret) {
+		DRM_ERROR("Failed to initialize connector\n");
+		return ret;
+	}
+
+	drm_bridge_set_connector_orientation(bridge, connector);
+
+	drm_connector_attach_encoder(connector, encoder);
+
+	if (bridge->dev->registered) {
+		if (connector->funcs->reset)
+			connector->funcs->reset(connector);
+		drm_connector_register(connector);
+	}
+
+	return 0;
+}
+
+static void drm_panel_bridge_detach(struct drm_bridge *bridge)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_connector *connector = &panel->connector;
+
+	/* Cleanup the connector if we know it was initialized */
+	if (connector->dev)
+		drm_connector_cleanup(connector);
+}
+
+static void drm_panel_bridge_atomic_pre_enable(struct drm_bridge *bridge,
+					       struct drm_atomic_commit *atomic_commit)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *old_crtc_state;
+
+	crtc = drm_atomic_get_new_crtc_for_encoder(atomic_commit, encoder);
+	if (!crtc)
+		return;
+
+	old_crtc_state = drm_atomic_get_old_crtc_state(atomic_commit, crtc);
+	if (old_crtc_state && old_crtc_state->self_refresh_active)
+		return;
+
+	drm_panel_prepare(panel);
+}
+
+static void drm_panel_bridge_atomic_enable(struct drm_bridge *bridge,
+					   struct drm_atomic_commit *atomic_commit)
 {
-	struct drm_panel *panel = container_of(kref, struct drm_panel, refcount);
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *old_crtc_state;
 
-	kfree(panel->container);
+	crtc = drm_atomic_get_new_crtc_for_encoder(atomic_commit, encoder);
+	if (!crtc)
+		return;
+
+	old_crtc_state = drm_atomic_get_old_crtc_state(atomic_commit, crtc);
+	if (old_crtc_state && old_crtc_state->self_refresh_active)
+		return;
+
+	drm_panel_enable(panel);
+}
+
+static void drm_panel_bridge_atomic_disable(struct drm_bridge *bridge,
+					    struct drm_atomic_commit *atomic_commit)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *new_crtc_state;
+
+	crtc = drm_atomic_get_old_crtc_for_encoder(atomic_commit, encoder);
+	if (!crtc)
+		return;
+
+	new_crtc_state = drm_atomic_get_new_crtc_state(atomic_commit, crtc);
+	if (new_crtc_state && new_crtc_state->self_refresh_active)
+		return;
+
+	drm_panel_disable(panel);
 }
 
+static void drm_panel_bridge_atomic_post_disable(struct drm_bridge *bridge,
+						 struct drm_atomic_commit *atomic_commit)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *new_crtc_state;
+
+	crtc = drm_atomic_get_old_crtc_for_encoder(atomic_commit, encoder);
+	if (!crtc)
+		return;
+
+	new_crtc_state = drm_atomic_get_new_crtc_state(atomic_commit, crtc);
+	if (new_crtc_state && new_crtc_state->self_refresh_active)
+		return;
+
+	drm_panel_unprepare(panel);
+}
+
+static int drm_panel_bridge_get_modes(struct drm_bridge *bridge,
+				      struct drm_connector *connector)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+
+	return drm_panel_get_modes(panel, connector);
+}
+
+static void drm_panel_bridge_debugfs_init(struct drm_bridge *bridge,
+					  struct dentry *root)
+{
+	struct drm_panel *panel = drm_bridge_to_panel(bridge);
+
+	root = debugfs_create_dir("panel", root);
+	if (panel->funcs->debugfs_init)
+		panel->funcs->debugfs_init(panel, root);
+}
+
+static const struct drm_bridge_funcs drm_panel_bridge_funcs = {
+	.attach = drm_panel_bridge_attach,
+	.detach = drm_panel_bridge_detach,
+	.atomic_pre_enable = drm_panel_bridge_atomic_pre_enable,
+	.atomic_enable = drm_panel_bridge_atomic_enable,
+	.atomic_disable = drm_panel_bridge_atomic_disable,
+	.atomic_post_disable = drm_panel_bridge_atomic_post_disable,
+	.get_modes = drm_panel_bridge_get_modes,
+	.atomic_create_state = drm_atomic_helper_bridge_create_state,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+	.atomic_get_input_bus_fmts = drm_atomic_helper_bridge_propagate_bus_fmt,
+	.debugfs_init = drm_panel_bridge_debugfs_init,
+};
+
 /**
  * drm_panel_get - Acquire a panel reference
  * @panel: DRM panel
@@ -387,10 +590,8 @@ static void __drm_panel_free(struct kref *kref)
  */
 struct drm_panel *drm_panel_get(struct drm_panel *panel)
 {
-	if (!panel)
-		return panel;
-
-	kref_get(&panel->refcount);
+	if (panel)
+		drm_bridge_get(&panel->bridge);
 
 	return panel;
 }
@@ -406,7 +607,7 @@ EXPORT_SYMBOL(drm_panel_get);
 void drm_panel_put(struct drm_panel *panel)
 {
 	if (panel)
-		kref_put(&panel->refcount, __drm_panel_free);
+		drm_bridge_put(&panel->bridge);
 }
 EXPORT_SYMBOL(drm_panel_put);
 
@@ -429,8 +630,22 @@ void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
 			     const struct drm_panel_funcs *funcs,
 			     int connector_type)
 {
-	void *container;
+	/*
+	 * Struct embedding and offsets:
+	 *
+	 *    |--------------- user container struct ------------|
+	 *    :    |---------- struct drm_panel ------------|
+	 *    :    :    |----- struct drm_bridge ------|
+	 *    A    B    C
+	 *
+	 * B - A = offset (passed as argument)
+	 * C - B = panel_bridge_offset
+	 * C - A = alloc_bridge_offset
+	 */
+	const size_t panel_bridge_offset = offsetof(struct drm_panel, bridge);
+	const size_t alloc_bridge_offset = offset + panel_bridge_offset;
 	struct drm_panel *panel;
+	void *container;
 	int err;
 
 	if (!funcs) {
@@ -438,14 +653,16 @@ void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
 		return ERR_PTR(-EINVAL);
 	}
 
-	container = kzalloc(size, GFP_KERNEL);
-	if (!container)
-		return ERR_PTR(-ENOMEM);
+	container = __devm_drm_bridge_alloc(dev, size, alloc_bridge_offset,
+					    &drm_panel_bridge_funcs);
+	if (IS_ERR(container))
+		return container;
 
 	panel = container + offset;
-	panel->container = container;
 	panel->funcs = funcs;
-	kref_init(&panel->refcount);
+	panel->bridge.of_node = dev->of_node;
+
+	drm_panel_get(panel);
 
 	err = devm_add_action_or_reset(dev, drm_panel_put_void, panel);
 	if (err)
@@ -457,6 +674,19 @@ void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
 }
 EXPORT_SYMBOL(__devm_drm_panel_alloc);
 
+/**
+ * drm_bridge_is_panel - Tell if a drm_bridge is a panel.
+ *
+ * @bridge: The drm_bridge to be checked.
+ *
+ * Returns true if the bridge is a panel, or false otherwise.
+ */
+bool drm_bridge_is_panel(const struct drm_bridge *bridge)
+{
+	return bridge->funcs == &drm_panel_bridge_funcs;
+}
+EXPORT_SYMBOL(drm_bridge_is_panel);
+
 #ifdef CONFIG_OF
 /**
  * of_drm_find_panel - look up and reference a panel by device tree node
diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
index 08949d41d743..7fe2f3160b2a 100644
--- a/include/drm/drm_panel.h
+++ b/include/drm/drm_panel.h
@@ -30,6 +30,8 @@
 #include <linux/mutex.h>
 #include <linux/kref.h>
 
+#include <drm/drm_bridge.h>
+
 struct backlight_device;
 struct dentry;
 struct device_node;
@@ -228,6 +230,22 @@ struct drm_panel {
 	 */
 	const struct drm_panel_funcs *funcs;
 
+	/**
+	 * @bridge:
+	 *
+	 * Bridge to access the panel features through the drm_bridge API.
+	 */
+	struct drm_bridge bridge;
+
+	/**
+	 * @connector:
+	 *
+	 * Connector instantiated by the bridge (only for legacy code not
+	 * yet using the drm_bridge_connector and
+	 * DRM_BRIDGE_ATTACH_NO_CONNECTOR).
+	 */
+	struct drm_connector connector;
+
 	/**
 	 * @connector_type:
 	 *
@@ -281,17 +299,6 @@ struct drm_panel {
 	 * If true then the panel has been enabled.
 	 */
 	bool enabled;
-
-	/**
-	 * @container: Pointer to the private driver struct embedding this
-	 * @struct drm_panel.
-	 */
-	void *container;
-
-	/**
-	 * @refcount: reference count of users referencing this panel.
-	 */
-	struct kref refcount;
 };
 
 void *__devm_drm_panel_alloc(struct device *dev, size_t size, size_t offset,
@@ -327,6 +334,10 @@ void drm_panel_add(struct drm_panel *panel);
 void drm_panel_remove(struct drm_panel *panel);
 int devm_drm_panel_add(struct device *dev, struct drm_panel *panel);
 
+bool drm_bridge_is_panel(const struct drm_bridge *bridge);
+int drm_bridge_set_connector_orientation(const struct drm_bridge *bridge,
+					 struct drm_connector *connector);
+
 void drm_panel_prepare(struct drm_panel *panel);
 void drm_panel_unprepare(struct drm_panel *panel);
 

-- 
2.55.0