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Mon, 29 Dec 2025 09:14:28 -0800 (PST) Date: Mon, 29 Dec 2025 18:14:26 +0100 From: =?iso-8859-1?Q?Jos=E9_Exp=F3sito?= To: Louis Chauvet Cc: Haneen Mohammed , Simona Vetter , Melissa Wen , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Jonathan Corbet , victoria@system76.com, sebastian.wick@redhat.com, thomas.petazzoni@bootlin.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v3 33/33] drm/vkms: Introduce configfs for dynamic connector creation Message-ID: References: <20251222-vkms-all-config-v3-0-ba42dc3fb9ff@bootlin.com> <20251222-vkms-all-config-v3-33-ba42dc3fb9ff@bootlin.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20251222-vkms-all-config-v3-33-ba42dc3fb9ff@bootlin.com> On Mon, Dec 22, 2025 at 11:11:35AM +0100, Louis Chauvet wrote: > 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 > Signed-off-by: José Expósito > Signed-off-by: Louis Chauvet > --- > 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//connectors//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//connectors//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//connectors//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; Since this rollback jumps out of the guard, there is a chance that, while the connector is "enabled" (enabled as in the variable) and before is set to "was_enabled", another thread is executed and reads an invalid value. The cleanup path needs to be inside the guard. Jose > + } > + > + 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 >