Thanks for the feedback.

On Sat, 15 Aug 2020 at 01:00, Imre Deak imre.deak@intel.com wrote:

On Wed, Jul 29, 2020 at 04:15:28PM +1000, Sam McNally wrote:

...

As of commit d8bd15b37d32 ("drm/dp_mst: Fix the DDC I2C device registration of an MST port"), DP MST DDC I2C devices are consistently parented to the underlying DRM device, making it challenging to associate the ddc i2c device with its connector from userspace.

I can't see how was it less challenging before the commit. There is no guarantee for a CSN message which was the only way for the i2c device to get reparented to the connector.

Yes, that's true - the state before and after are both unable to support ddc reliable i2c device discovery, and consistency is better. The challenging part certainly is an ongoing affair - I wasn't intending to blame it on that commit, though it has come out that way, unfortunately. Looking at it now, that paragraph doesn't need to reference any commits in particular; I'll rewrite it for the next version.

...

Given the need for further refactoring before the i2c devices can be parented to their connectors, in the meantime follow the pattern of commit e1a29c6c5955 ("drm: Add ddc link in sysfs created by drm_connector"), creating sysfs ddc links to the associated i2c device for MST DP connectors.

If the connector is created and registered before the i2c device, create the link when registering the i2c device; otherwise, create the link during late connector registration.

Signed-off-by: Sam McNally sammc@chromium.org

drivers/gpu/drm/drm_dp_mst_topology.c | 29 +++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 1ac874e4e7a1..73a2299c2faa 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -2161,11 +2161,23 @@ static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb, int drm_dp_mst_connector_late_register(struct drm_connector *connector, struct drm_dp_mst_port *port) {

• int ret;
  DRM_DEBUG_KMS("registering %s remote bus for %s\n",
                port->aux.name, connector->kdev->kobj.name);
  
  port->aux.dev = connector->kdev;
  

• return drm_dp_aux_register_devnode(&port->aux);
  

• ret = drm_dp_aux_register_devnode(&port->aux);
  

• if (ret)
  

•         return ret;
  

• if (port->pdt != DP_PEER_DEVICE_NONE &&
  

•     drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
  

How can we get here when drm_dp_mst_is_end_device(port) is not true? AFAICS that's only case where we should create a connector and an i2c device. (IOW we don't create them for branch ports.)

I'm not sure what you mean. Wouldn't this condition be checked during the registration of any MST connector? This follows the pattern used in drm_dp_mst_port_add_connector() [0], which seems like it's invoked in the same cases as drm_dp_mst_connector_late_register(), modulo early outs for errors.

[0] https://cgit.freedesktop.org/drm-tip/tree/drivers/gpu/drm/drm_dp_mst_topolog...

...

•         ret = sysfs_create_link(&port->connector->kdev->kobj,
  

•                                 &port->aux.ddc.dev.kobj, "ddc");
  

•         if (ret)
  

•                 drm_dp_aux_unregister_devnode(&port->aux);
  

• }
  

• return ret;
  

} EXPORT_SYMBOL(drm_dp_mst_connector_late_register);

@@ -5490,6 +5502,7 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) { struct drm_dp_aux *aux = &port->aux; struct device *parent_dev = port->mgr->dev->dev;

• int ret;
  
  aux->ddc.algo = &drm_dp_mst_i2c_algo;
  aux->ddc.algo_data = aux;
  

@@ -5504,7 +5517,17 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev), sizeof(aux->ddc.name));

• return i2c_add_adapter(&aux->ddc);
  

• ret = i2c_add_adapter(&aux->ddc);
  

• if (ret)
  

•         return ret;
  

• if (port->connector && port->connector->kdev) {
  

•         ret = sysfs_create_link(&port->connector->kdev->kobj,
  

•                                 &port->aux.ddc.dev.kobj, "ddc");
  

•         if (ret)
  

•                 i2c_del_adapter(&port->aux.ddc);
  

• }
  

• return ret;
  

}

/** @@ -5513,6 +5536,8 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) */ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port) {

• if (port->connector && port->connector->kdev)
  

•         sysfs_remove_link(&port->connector->kdev->kobj, "ddc");
  i2c_del_adapter(&port->aux.ddc);
  

}

-- 2.28.0.rc0.142.g3c755180ce-goog

On Thu, 2020-08-20 at 21:03 +0300, Imre Deak wrote:

On Thu, Aug 20, 2020 at 12:27:03PM +1000, Sam McNally wrote:

...

...

...

[...] diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 1ac874e4e7a1..73a2299c2faa 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -2161,11 +2161,23 @@ static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb, int drm_dp_mst_connector_late_register(struct drm_connector *connector, struct drm_dp_mst_port *port) {

• int ret;
  DRM_DEBUG_KMS("registering %s remote bus for %s\n",
                port->aux.name, connector->kdev->kobj.name);
  
  port->aux.dev = connector->kdev;
  

• return drm_dp_aux_register_devnode(&port->aux);
  

• ret = drm_dp_aux_register_devnode(&port->aux);
  

• if (ret)
  

•         return ret;
  

• if (port->pdt != DP_PEER_DEVICE_NONE &&
  

•     drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
  

How can we get here when drm_dp_mst_is_end_device(port) is not true? AFAICS that's only case where we should create a connector and an i2c device. (IOW we don't create them for branch ports.)

I'm not sure what you mean. Wouldn't this condition be checked during the registration of any MST connector? This follows the pattern used in drm_dp_mst_port_add_connector() [0], which seems like it's invoked in the same cases as drm_dp_mst_connector_late_register(), modulo early outs for errors.

Re-reading the code, a DRM connector is created whenever the MST port is an output port, so even in the case of an output branch port.

I'm still not sure why we can't register/unregister the I2C bus whenever creating/removing the DRM connector. That's also the scope of the AUX bus, which is what I2C depends on, and if a port doesn't support I2C messaging then the corresponding AUX messages would be NAKed.

FWIW - I'm totally fine with this, as long as it works :)

--Imre

...

[0] https://cgit.freedesktop.org/drm-tip/tree/drivers/gpu/drm/drm_dp_mst_topolog...

...

...

•         ret = sysfs_create_link(&port->connector->kdev->kobj,
  

•                                 &port->aux.ddc.dev.kobj, "ddc");
  

•         if (ret)
  

•                 drm_dp_aux_unregister_devnode(&port->aux);
  

• }
  

• return ret;
  

} EXPORT_SYMBOL(drm_dp_mst_connector_late_register);

@@ -5490,6 +5502,7 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) { struct drm_dp_aux *aux = &port->aux; struct device *parent_dev = port->mgr->dev->dev;

• int ret;
  
  aux->ddc.algo = &drm_dp_mst_i2c_algo;
  aux->ddc.algo_data = aux;
  

@@ -5504,7 +5517,17 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(parent_dev), sizeof(aux->ddc.name));

• return i2c_add_adapter(&aux->ddc);
  

• ret = i2c_add_adapter(&aux->ddc);
  

• if (ret)
  

•         return ret;
  

• if (port->connector && port->connector->kdev) {
  

•         ret = sysfs_create_link(&port->connector->kdev->kobj,
  

•                                 &port->aux.ddc.dev.kobj, "ddc");
  

•         if (ret)
  

•                 i2c_del_adapter(&port->aux.ddc);
  

• }
  

• return ret;
  

}

/** @@ -5513,6 +5536,8 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port) */ static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port) {

• if (port->connector && port->connector->kdev)
  

•         sysfs_remove_link(&port->connector->kdev->kobj, "ddc");
  i2c_del_adapter(&port->aux.ddc);
  

}

-- 2.28.0.rc0.142.g3c755180ce-goog