[PATCH v3 33/33] drm/vkms: Introduce configfs for dynamic connector creation

Louis Chauvet
2025-12-22T10:12:55Z

DRM allows the connector to be created after the device. To allows
emulating this, add two configfs attributes to connector to allows this.

Using the dynamic attribute you can set if a connector will be dynamic or
not.
Using the enabled attribute, you can set at runtime if a dynamic connector
is present or not.

Co-developed-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
---
Documentation/ABI/testing/configfs-vkms | 14 +++
Documentation/gpu/vkms.rst | 6 +-
drivers/gpu/drm/vkms/vkms_configfs.c | 146 ++++++++++++++++++++++++++++++--
3 files changed, 155 insertions(+), 11 deletions(-)

diff --git a/Documentation/ABI/testing/configfs-vkms b/Documentation/ABI/testing/configfs-vkms
index 4061ada5d88b..a7fce35fcf91 100644
--- a/Documentation/ABI/testing/configfs-vkms
+++ b/Documentation/ABI/testing/configfs-vkms
@@ -62,6 +62,20 @@ Description:
Content of the EDID for this connector. Ignored if
edid_enabled is not set.

+What: /sys/kernel/config/vkms/<device>/connectors/<connector>/dynamic
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ Set to 1 to create a dynamic connector (emulates DP MST).
+ Value: 1 - dynamic, 0 - static.
+
+What: /sys/kernel/config/vkms/<device>/connectors/<connector>/enabled
+Date: Nov 2025
+Contact: dri-devel@lists.freedesktop.org
+Description:
+ For dynamic connectors, set to 1 to create the connector,
+ 0 to remove it. Value: 1 - enabled, 0 - disabled.
+
What: /sys/kernel/config/vkms/<device>/connectors/<connector>/possible_encoders
Date: Nov 2025
Contact: dri-devel@lists.freedesktop.org
diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 60367fd1bd65..fce229fbfc7c 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -138,7 +138,7 @@ Last but not least, create one or more connectors::

sudo mkdir /config/vkms/my-vkms/connectors/connector0

-Connectors have 5 configurable attribute:
+Connectors have 7 configurable attribute:

- status: Connection status: 1 connected, 2 disconnected, 3 unknown (same values
as those exposed by the "status" property of a connector)
@@ -150,7 +150,9 @@ Connectors have 5 configurable attribute:
- edid_enabled: Enable or not EDID for this connector. Some connectors may not have an
EDID but just a list of modes, this attribute allows to disable EDID property.
- edid: Content of the EDID. Ignored if edid_enabled is not set
-
+- dynamic: Set to 1 while configuring the device to create a dynamic connector. A dynamic
+ connector can be used to emulate DP MST connectors.
+- enabled: For dynamic connector, set it to 1 to create the connector, 0 to remove it.

To finish the configuration, link the different pipeline items::

diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 20f5150e8b24..657381a8a4c2 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -1144,6 +1144,12 @@ static ssize_t connector_status_show(struct config_item *item, char *page)
return sprintf(page, "%u", status);
}

+static bool connector_is_enabled(struct vkms_config_connector *connector_cfg)
+{
+ return !connector_cfg->dynamic ||
+ (connector_cfg->dynamic && connector_cfg->enabled);
+}
+
static ssize_t connector_status_store(struct config_item *item,
const char *page, size_t count)
{
@@ -1163,7 +1169,7 @@ static ssize_t connector_status_store(struct config_item *item,
scoped_guard(mutex, &connector->dev->lock) {
vkms_config_connector_set_status(connector->config, status);

- if (connector->dev->enabled)
+ if (connector->dev->enabled && connector_is_enabled(connector->config))
vkms_trigger_connector_hotplug(connector->dev->config->dev);
}

@@ -1224,7 +1230,7 @@ static ssize_t connector_type_store(struct config_item *item,
}

scoped_guard(mutex, &connector->dev->lock) {
- if (connector->dev->enabled)
+ if (connector->dev->enabled && connector_is_enabled(connector->config))
return -EBUSY;

vkms_config_connector_set_type(connector->config, val);
@@ -1343,6 +1349,107 @@ static ssize_t connector_edid_store(struct config_item *item,
connector_status_disconnected)
vkms_trigger_connector_hotplug(connector->dev->config->dev);
}
+ return count;
+}
+
+static ssize_t connector_enabled_show(struct config_item *item, char *page)
+{
+ struct vkms_configfs_connector *connector;
+ bool enabled;
+
+ connector = connector_item_to_vkms_configfs_connector(item);
+
+ scoped_guard(mutex, &connector->dev->lock)
+ enabled = vkms_config_connector_is_enabled(connector->config);
+
+ return sprintf(page, "%d\n", enabled);
+}
+
+static ssize_t connector_enabled_store(struct config_item *item,
+ const char *page, size_t count)
+{
+ struct vkms_configfs_connector *connector;
+ struct vkms_config_connector *connector_cfg;
+ bool enabled, was_enabled;
+
+ connector = connector_item_to_vkms_configfs_connector(item);
+ connector_cfg = connector->config;
+
+ if (kstrtobool(page, &enabled))
+ return -EINVAL;
+ scoped_guard(mutex, &connector->dev->lock) {
+ if (!connector->dev->enabled) {
+ vkms_config_connector_set_enabled(connector_cfg, enabled);
+ } else {
+ // Only dynamic connector can be enabled/disabled at runtime
+ if (!connector_cfg->dynamic)
+ return -EBUSY;
+
+ was_enabled = vkms_config_connector_is_enabled(connector_cfg);
+ vkms_config_connector_set_enabled(connector_cfg, enabled);
+
+ // Resulting configuration is invalid (missing encoder for example)
+ // Early return to avoid drm core issue
+ if (!vkms_config_is_valid(connector->dev->config)) {
+ count = -EINVAL;
+ goto rollback;
+ }
+
+ if (!was_enabled && enabled) {
+ // Adding the connector
+ connector_cfg->connector = vkms_connector_hot_add(connector->dev->config->dev,
+ connector_cfg);
+ if (IS_ERR(connector_cfg->connector)) {
+ count = PTR_ERR(connector_cfg->connector);
+ goto rollback;
+ }
+ } else if (was_enabled && !enabled) {
+ vkms_connector_hot_remove(connector->dev->config->dev,
+ connector_cfg->connector);
+ }
+ }
+ }
+ return count;
+
+rollback:
+ vkms_config_connector_set_enabled(connector_cfg, was_enabled);
+ return count;
+}
+
+static ssize_t connector_dynamic_show(struct config_item *item, char *page)
+{
+ struct vkms_configfs_connector *connector;
+ bool enabled;
+
+ connector = connector_item_to_vkms_configfs_connector(item);
+
+ scoped_guard(mutex, &connector->dev->lock) {
+ enabled = vkms_config_connector_is_dynamic(connector->config);
+ }
+
+ return sprintf(page, "%d\n", enabled);
+}
+
+static ssize_t connector_dynamic_store(struct config_item *item,
+ const char *page, size_t count)
+{
+ struct vkms_configfs_connector *connector;
+ struct vkms_config_connector *connector_cfg;
+ bool dynamic;
+
+ connector = connector_item_to_vkms_configfs_connector(item);
+ connector_cfg = connector->config;
+
+ if (kstrtobool(page, &dynamic))
+ return -EINVAL;
+
+ scoped_guard(mutex, &connector->dev->lock) {
+ // Can't change the dynamic status when the device is activated
+ if (connector->dev->enabled)
+ return -EBUSY;
+
+ vkms_config_connector_set_dynamic(connector_cfg, dynamic);
+ }

return count;
}
@@ -1352,6 +1459,8 @@ CONFIGFS_ATTR(connector_, type);
CONFIGFS_ATTR(connector_, supported_colorspaces);
CONFIGFS_ATTR(connector_, edid_enabled);
CONFIGFS_ATTR(connector_, edid);
+CONFIGFS_ATTR(connector_, dynamic);
+CONFIGFS_ATTR(connector_, enabled);

static struct configfs_attribute *connector_item_attrs[] = {
&connector_attr_status,
@@ -1359,19 +1468,28 @@ static struct configfs_attribute *connector_item_attrs[] = {
&connector_attr_supported_colorspaces,
&connector_attr_edid_enabled,
&connector_attr_edid,
+ &connector_attr_dynamic,
+ &connector_attr_enabled,
NULL,
};

static void connector_release(struct config_item *item)
{
struct vkms_configfs_connector *connector;
+ struct vkms_config_connector *connector_cfg;
struct mutex *lock;

connector = connector_item_to_vkms_configfs_connector(item);
+ connector_cfg = connector->config;
lock = &connector->dev->lock;

scoped_guard(mutex, lock) {
+ if (connector->dev->enabled && connector_cfg->dynamic && connector_cfg->enabled)
+ vkms_connector_hot_remove(connector->dev->config->dev,
+ connector_cfg->connector);
+
vkms_config_destroy_connector(connector->config);
+
kfree(connector);
}
}
@@ -1390,6 +1508,7 @@ static int connector_possible_encoders_allow_link(struct config_item *src,
struct config_item *target)
{
struct vkms_configfs_connector *connector;
+ struct vkms_config_connector *connector_cfg;
struct vkms_configfs_encoder *encoder;
int ret;

@@ -1397,16 +1516,26 @@ static int connector_possible_encoders_allow_link(struct config_item *src,
return -EINVAL;

connector = connector_possible_encoders_item_to_vkms_configfs_connector(src);
+ connector_cfg = connector->config;
encoder = encoder_item_to_vkms_configfs_encoder(target);

scoped_guard(mutex, &connector->dev->lock) {
- if (connector->dev->enabled)
- return -EBUSY;
+ if (connector->dev->enabled && connector_cfg->enabled) {
+ if (!connector_cfg->dynamic)
+ return -EBUSY;
+
+ ret = vkms_connector_hot_attach_encoder(connector->dev->config->dev,
+ connector->config->connector,
+ encoder->config->encoder);
+ if (ret)
+ return ret;
+ }

ret = vkms_config_connector_attach_encoder(connector->config,
encoder->config);
+ if (ret)
+ return ret;
}
-
return ret;
}

@@ -1445,9 +1574,6 @@ static struct config_group *make_connector_group(struct config_group *group,
dev = child_group_to_vkms_configfs_device(group);

scoped_guard(mutex, &dev->lock) {
- if (dev->enabled)
- return ERR_PTR(-EBUSY);
-
connector = kzalloc(sizeof(*connector), GFP_KERNEL);
if (!connector)
return ERR_PTR(-ENOMEM);
@@ -1461,9 +1587,11 @@ static struct config_group *make_connector_group(struct config_group *group,
return ERR_PTR(ret);
}

+ vkms_config_connector_set_dynamic(connector->config, connector->dev->enabled);
+ vkms_config_connector_set_enabled(connector->config, !connector->dev->enabled);
+
config_group_init_type_name(&connector->group, name,
&connector_item_type);
-
config_group_init_type_name(&connector->possible_encoders_group,
"possible_encoders",
&connector_possible_encoders_group_type);

--
2.51.2