Hello Luca,
On 11/11/2025 11:14 PM, Luca Ceresoli wrote:
Hello Chaoyi,
On Tue Nov 11, 2025 at 11:50 AM CET, Chaoyi Chen wrote:
From: Chaoyi Chen <[email protected]>
The RK3399 has two USB/DP combo PHY and one CDN-DP controller. And
the CDN-DP can be switched to output to one of the PHYs. If both ports
are plugged into DP, DP will select the first port for output.
This patch adds support for multiple bridges, enabling users to flexibly
select the output port. For each PHY port, a separate encoder and bridge
are registered.
The change is based on the DRM AUX HPD bridge, rather than the
extcon approach. This requires the DT to correctly describe the
connections between the first bridge in bridge chain and DP
controller. For example, the bridge chain may be like this:
PHY aux birdge -> fsa4480 analog audio switch bridge ->
onnn,nb7vpq904m USB reminder bridge -> USB-C controller AUX HPD bridge
In this case, the connection relationships among the PHY aux bridge
and the DP contorller need to be described in DT.
In addition, the cdn_dp_parse_next_bridge_dt() will parses it and
determines whether to register one or two bridges.
Since there is only one DP controller, only one of the PHY ports can
output at a time. The key is how to switch between different PHYs,
which is handled by cdn_dp_switch_port() and cdn_dp_enable().
There are two cases:
1. Neither bridge is enabled. In this case, both bridges can
independently read the EDID, and the PHY port may switch before
reading the EDID.
2. One bridge is already enabled. In this case, other bridges are not
allowed to read the EDID. So we will try to return the cached EDID.
Since the scenario of two ports plug in at the same time is rare,
I don't have a board which support two TypeC connector to test this.
Therefore, I tested forced switching on a single PHY port, as well as
output using a fake PHY port alongside a real PHY port.
Signed-off-by: Chaoyi Chen <[email protected]>
[...]
@@ -966,28 +1084,16 @@ static int cdn_dp_pd_event(struct notifier_block *nb,
return NOTIFY_DONE;
}
-static int cdn_dp_bind(struct device *dev, struct device *master, void *data)
+static int cdn_bridge_add(struct device *dev,
+ struct drm_bridge *bridge,
+ struct drm_bridge *next_bridge,
+ struct drm_encoder *encoder)
{
struct cdn_dp_device *dp = dev_get_drvdata(dev);
- struct drm_encoder *encoder;
+ struct drm_device *drm_dev = dp->drm_dev;
+ struct drm_bridge *last_bridge = NULL;
struct drm_connector *connector;
- struct cdn_dp_port *port;
- struct drm_device *drm_dev = data;
- int ret, i;
[...]
+ if (next_bridge) {
+ ret = drm_bridge_attach(encoder, next_bridge, bridge,
+ DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+ if (ret)
+ return ret;
+
+ last_bridge = next_bridge;
+ while (drm_bridge_get_next_bridge(last_bridge))
+ last_bridge = drm_bridge_get_next_bridge(last_bridge);
DRM bridges are now refcounted, and you are not calling drm_bridge_get()
and drm_bridge_put() here. But here you can use
drm_bridge_chain_get_last_bridge() which will simplify your job.
Don't forget to call drm_bridge_put() on the returned bridge when the
bridge is not referenced anymore. This should be as easy as adding a
cleanup action on the variable declaration above:
- struct drm_bridge *last_bridge = NULL;
+ struct drm_bridge *last_bridge __free(drm_bridge_put) = NULL;
Ah, I have seen your patch about this. Thank you for the reminder, I will fix
this in v10.
@@ -1029,8 +1147,102 @@ static int cdn_dp_bind(struct device *dev, struct
device *master, void *data)
return ret;
}
+ if (last_bridge)
+ connector->fwnode =
fwnode_handle_get(of_fwnode_handle(last_bridge->of_node));
+
drm_connector_attach_encoder(connector, encoder);
+ return 0;
+}
+
+static int cdn_dp_parse_next_bridge_dt(struct cdn_dp_device *dp)
+{
+ struct device_node *np = dp->dev->of_node;
+ struct device_node *port __free(device_node) =
of_graph_get_port_by_id(np, 1);
+ struct drm_bridge *bridge;
+ int count = 0;
+ int ret = 0;
+ int i;
+
+ /* If device use extcon, do not use hpd bridge */
+ for (i = 0; i < dp->ports; i++) {
+ if (dp->port[i]->extcon) {
+ dp->bridge_count = 1;
+ return 0;
+ }
+ }
+
+
+ /* One endpoint may correspond to one next bridge. */
+ for_each_of_graph_port_endpoint(port, dp_ep) {
+ struct device_node *next_bridge_node __free(device_node) =
+ of_graph_get_remote_port_parent(dp_ep);
+
+ bridge = of_drm_find_bridge(next_bridge_node);
+ if (!bridge) {
+ ret = -EPROBE_DEFER;
+ goto out;
+ }
+
+ dp->next_bridge_valid = true;
+ dp->next_bridge_list[count].bridge = bridge;
You are storing a reference to a drm_bridge, so have to increment the
refcount:
dp->next_bridge_list[count].bridge = drm_bridge_get(bridge);
^^^^^^^^^^^^^^
FYI there is a plan to replace of_drm_find_bridge() with a function that
increases the bridge refcount before returning the bridge, but it's not
there yet. When that will happen, the explicit drm_bridge_get() won't be
needed anymore and this code can be updated accordingly.
Also you have to call drm_bridge_put() to release that reference when the
pointer goes away. I guess that should happen in cdn_dp_unbind().
You're right, this is indeed a pitfall. I will fix it in v10.
+static int cdn_dp_bind(struct device *dev, struct device *master, void *data)
+{
In this function you do:
...(see below)...
+ struct cdn_dp_device *dp = dev_get_drvdata(dev);
+ struct drm_bridge *bridge, *next_bridge;
+ struct drm_encoder *encoder;
+ struct cdn_dp_port *port;
+ struct drm_device *drm_dev = data;
+ struct cdn_dp_bridge *dp_bridge;
+ int ret, i;
+
+ ret = cdn_dp_parse_dt(dp);
+ if (ret < 0)
.> + return ret;
+
+ ret = cdn_dp_parse_next_bridge_dt(dp);
1. compute the next bridges and store them in dp->next_bridge_list[]
...
+ if (ret)
+ return ret;
+
+ dp->drm_dev = drm_dev;
+ dp->connected = false;
+ dp->active = false;
+ dp->active_port = -1;
+ dp->fw_loaded = false;
+
+ for (i = 0; i < dp->bridge_count; i++) {
+ dp_bridge = devm_drm_bridge_alloc(dev, struct cdn_dp_bridge,
bridge,
+ &cdn_dp_bridge_funcs);
+ if (IS_ERR(dp_bridge))
+ return PTR_ERR(dp_bridge);
+ dp_bridge->id = i;
+ dp_bridge->parent = dp;
+ if (!dp->next_bridge_valid)
+ dp_bridge->connected = true;
+ dp->bridge_list[i] = dp_bridge;
+ }
+
+ for (i = 0; i < dp->bridge_count; i++) {
+ encoder = &dp->bridge_list[i]->encoder.encoder;
+ bridge = &dp->bridge_list[i]->bridge;
+ next_bridge = dp->next_bridge_list[i].bridge;
+ ret = cdn_bridge_add(dev, bridge, next_bridge, encoder);
...
2. pass the dp->next_bridge_list[i].bridge to cdn_bridge_add
3. not use dp->next_bridge_list[i] elsewhere
So you may want to change this function to parse into a local array, with
function scope. If you do this, the drm_bridge_get/put() I mentioned above
should still exist, but would be localized to this function, thus even
easier to handle.
Even better, you can parse the DT one bridge at a time inside the for loop,
so you don't need to store any next_bridge pointer array. This will need a
bit of rework of cdn_dp_parse_next_bridge_dt() though, and I haven't
checked in detail so it might be not worth.
The next_bridge is obtained through of_drm_find_bridge(). According to your
description just now, drm_bridge_put() needs to be called in cdn_dp_unbind().
So if I understand correctly, we do need to store this pointer.
[...]
+struct cdn_dp_bridge {
+ struct cdn_dp_device *parent;
+ struct drm_bridge bridge;
+ struct rockchip_encoder encoder;
+ bool connected;
+ bool enabled;
+ int id;
+};
+
+struct cdn_dp_next_bridge {
+ struct cdn_dp_device *parent;
+ struct drm_bridge *bridge;
+ int id;
The @parent and @id fields are unused if I'm not mistaken.
If it is the case then you can... (see below)
struct cdn_dp_device {
struct device *dev;
struct drm_device *drm_dev;
- struct drm_bridge bridge;
- struct rockchip_encoder encoder;
+ int bridge_count;
+ struct cdn_dp_bridge *bridge_list[MAX_PHY];
+ struct cdn_dp_next_bridge next_bridge_list[MAX_PHY];
...replace this line with:
struct drm_bridge *next_bridge[MAX_PHY];
Unless of course you just don't store the next_bridge at all, as I
suggested above, and which looks way easier and more efficient.
Yes, the structure cdn_dp_next_bridge is only reserved for future expansion. I
will replace it with a simpler struct drm_bridge in v10.
--
Best,
Chaoyi
