Re: [PATCH v3 01/11] drm/connector: Add a way to init/add a connector in separate steps

[Imre Deak <imre.deak@intel.com>]

On Thu, Dec 12, 2024 at 12:04:17PM +0200, Jani Nikula wrote:
> On Thu, 12 Dec 2024, Imre Deak <imre.deak@intel.com> wrote:
> > Atm when the connector is added to the drm_mode_config::connector_list,
> > the connector may not be fully initialized yet. This is not a problem
> > for static connectors initialized/added during driver loading, for which
> > the driver ensures that look-ups via the above list are not possible
> > until all the connector and other required state is fully initialized
> > already. It's also not a problem for user space looking up either a
> > static or dynamic (see what this is below) connector, since this will be
> > only possible once the connector is registered.
> >
> > A dynamic - atm only a DP MST - connector can be initialized and added
> > after the load time initialization is done. Such a connector may be
> > looked up by in-kernel users once it's added to the connector list. In
> > particular a hotplug handler could perform a detection on all the
> > connectors on the list and hence find a connector there which isn't yet
> > initialized. For instance the connector's helper hooks may be unset,
> > leading to a NULL dereference while the detect helper calls the
> > connector's drm_connector_helper_funcs::detect() or detect_ctx()
> > handler.
> >
> > To resolve the above issue, add a way for dynamic connectors to
> > separately initialize the DRM core specific parts of the connector
> > without adding it to the connector list - by calling the new
> > drm_connector_dynamic_init() - and to add the connector to the list
> > later once all the initialization is complete and the connector is
> > registered - by calling the new drm_connector_dynamic_register().
> >
> > Adding the above 2 functions was also motivated to make the distinction
> > of the interface between static and dynamic connectors clearer: Drivers
> > should manually initialize and register only dynamic connectors (with
> > the above 2 functions). A driver should only initialize a static
> > connector (with one of the drm_connector_init*, drmm_connector_init*
> > functions) while the registration of the connector will be done
> > automatically by DRM core.
> >
> > v2: (Jani)
> > - Let initing DDC as well via drm_connector_init_core().
> > - Rename __drm_connector_init to drm_connector_init_core_and_add().
> >
> > v3:
> > - Rename drm_connector_init_core() to drm_connector_dynamic_init().
> >   (Sima)
> > - Instead of exporting drm_connector_add(), move adding the connector
> >   to the registration step via a new drm_connector_dynamic_register().
> >   (Sima)
> > - Update drm_connector_dynamic_init()'s function documentation and the
> >   commit log according to the above changes.
> > - Update the commit log describing the problematic scenario during
> >   connector detection. (Maxime)
> >
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Simona Vetter <simona@ffwll.ch>
> > Cc: Maxime Ripard <mripard@kernel.org>
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> (v1)
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> 
> Overall
> 
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Thanks.

> with some non-blocking subjective nitpicks inline.
> 
> > ---
> >  drivers/gpu/drm/drm_connector.c | 150 +++++++++++++++++++++++++++-----
> >  include/drm/drm_connector.h     |   6 ++
> >  2 files changed, 136 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > index fc35f47e2849e..a53e5629ba6c1 100644
> > --- a/drivers/gpu/drm/drm_connector.c
> > +++ b/drivers/gpu/drm/drm_connector.c
> > @@ -218,11 +218,11 @@ void drm_connector_free_work_fn(struct work_struct *work)
> >  	}
> >  }
> >  
> > -static int __drm_connector_init(struct drm_device *dev,
> > -				struct drm_connector *connector,
> > -				const struct drm_connector_funcs *funcs,
> > -				int connector_type,
> > -				struct i2c_adapter *ddc)
> > +static int drm_connector_init_only(struct drm_device *dev,
> > +				   struct drm_connector *connector,
> > +				   const struct drm_connector_funcs *funcs,
> > +				   int connector_type,
> > +				   struct i2c_adapter *ddc)
> >  {
> >  	struct drm_mode_config *config = &dev->mode_config;
> >  	int ret;
> > @@ -273,6 +273,7 @@ static int __drm_connector_init(struct drm_device *dev,
> >  	/* provide ddc symlink in sysfs */
> >  	connector->ddc = ddc;
> >  
> > +	INIT_LIST_HEAD(&connector->head);
> 
> Side note, it's confusing the node is called a head, and its
> documentation actually describes it as a "list of all connectors".
> 
> >  	INIT_LIST_HEAD(&connector->global_connector_list_entry);
> >  	INIT_LIST_HEAD(&connector->probed_modes);
> >  	INIT_LIST_HEAD(&connector->modes);
> > @@ -288,14 +289,6 @@ static int __drm_connector_init(struct drm_device *dev,
> >  
> >  	drm_connector_get_cmdline_mode(connector);
> >  
> > -	/* We should add connectors at the end to avoid upsetting the connector
> > -	 * index too much.
> > -	 */
> > -	spin_lock_irq(&config->connector_list_lock);
> > -	list_add_tail(&connector->head, &config->connector_list);
> > -	config->num_connector++;
> > -	spin_unlock_irq(&config->connector_list_lock);
> > -
> >  	if (connector_type != DRM_MODE_CONNECTOR_VIRTUAL &&
> >  	    connector_type != DRM_MODE_CONNECTOR_WRITEBACK)
> >  		drm_connector_attach_edid_property(connector);
> > @@ -332,6 +325,58 @@ static int __drm_connector_init(struct drm_device *dev,
> >  	return ret;
> >  }
> >  
> > +static void drm_connector_add(struct drm_connector *connector)
> > +{
> > +	struct drm_device *dev = connector->dev;
> > +	struct drm_mode_config *config = &dev->mode_config;
> > +
> > +	/*
> > +	 * TODO: Change this to a WARN, once all drivers are converted to
> > +	 * call drm_connector_dynamic_init() for MST connectors.
> > +	 */
> > +	if (!list_empty(&connector->head))
> > +		return;
> > +
> > +	spin_lock_irq(&config->connector_list_lock);
> > +	list_add_tail(&connector->head, &config->connector_list);
> > +	config->num_connector++;
> > +	spin_unlock_irq(&config->connector_list_lock);
> > +}
> > +
> > +static void drm_connector_remove(struct drm_connector *connector)
> > +{
> > +	struct drm_device *dev = connector->dev;
> > +
> > +	/*
> > +	 * For dynamic connectors drm_connector_cleanup() can call this function
> > +	 * before the connector is registered and added to the list.
> > +	 */
> > +	if (list_empty(&connector->head))
> > +		return;
> > +
> > +	spin_lock_irq(&dev->mode_config.connector_list_lock);
> > +	list_del_init(&connector->head);
> > +	dev->mode_config.num_connector--;
> > +	spin_unlock_irq(&dev->mode_config.connector_list_lock);
> > +}
> 
> I think there's a bit much going on in this patch, and the splitting of
> the above functions could've been a separate prep patch.

Ok, agreed, can do that if I need to resend the patchset.

> > +
> > +static int drm_connector_init_and_add(struct drm_device *dev,
> > +				      struct drm_connector *connector,
> > +				      const struct drm_connector_funcs *funcs,
> > +				      int connector_type,
> > +				      struct i2c_adapter *ddc)
> > +{
> > +	int ret;
> > +
> > +	ret = drm_connector_init_only(dev, connector, funcs, connector_type, ddc);
> > +	if (ret)
> > +		return ret;
> > +
> > +	drm_connector_add(connector);
> > +
> > +	return 0;
> > +}
> > +
> >  /**
> >   * drm_connector_init - Init a preallocated connector
> >   * @dev: DRM device
> > @@ -361,10 +406,51 @@ int drm_connector_init(struct drm_device *dev,
> >  	if (drm_WARN_ON(dev, !(funcs && funcs->destroy)))
> >  		return -EINVAL;
> >  
> > -	return __drm_connector_init(dev, connector, funcs, connector_type, NULL);
> > +	return drm_connector_init_and_add(dev, connector, funcs, connector_type, NULL);
> >  }
> >  EXPORT_SYMBOL(drm_connector_init);
> >  
> > +/**
> > + * drm_connector_dynamic_init - Init a preallocated dynamic connector
> > + * @dev: DRM device
> > + * @connector: the connector to init
> > + * @funcs: callbacks for this connector
> > + * @connector_type: user visible type of the connector
> > + * @ddc: pointer to the associated ddc adapter
> > + *
> > + * Initialises a preallocated dynamic connector. Connectors should be
> > + * subclassed as part of driver connector objects. The connector
> > + * structure should not be allocated with devm_kzalloc().
> > + *
> > + * Drivers should call this for dynamic connectors which can be hotplugged
> > + * after drm_dev_register() has been called already, e.g. DP MST connectors.
> > + * For all other - static - connectors, drivers should call one of the
> > + * drm_connector_init*()/drmm_connector_init*() functions.
> > + *
> > + * After calling this function the drivers must call
> > + * drm_connector_dynamic_register().
> > + *
> > + * To remove the connector the driver must call drm_connector_unregister()
> > + * followed by drm_connector_put(). Putting the last reference will call the
> > + * driver's &drm_connector_funcs.destroy hook, which in turn must call
> > + * drm_connector_cleanup() and free the connector structure.
> > + *
> > + * Returns:
> > + * Zero on success, error code on failure.
> > + */
> > +int drm_connector_dynamic_init(struct drm_device *dev,
> > +			       struct drm_connector *connector,
> > +			       const struct drm_connector_funcs *funcs,
> > +			       int connector_type,
> > +			       struct i2c_adapter *ddc)
> > +{
> > +	if (drm_WARN_ON(dev, !(funcs && funcs->destroy)))
> > +		return -EINVAL;
> > +
> > +	return drm_connector_init_only(dev, connector, funcs, connector_type, ddc);
> > +}
> > +EXPORT_SYMBOL(drm_connector_dynamic_init);
> > +
> >  /**
> >   * drm_connector_init_with_ddc - Init a preallocated connector
> >   * @dev: DRM device
> > @@ -398,7 +484,7 @@ int drm_connector_init_with_ddc(struct drm_device *dev,
> >  	if (drm_WARN_ON(dev, !(funcs && funcs->destroy)))
> >  		return -EINVAL;
> >  
> > -	return __drm_connector_init(dev, connector, funcs, connector_type, ddc);
> > +	return drm_connector_init_and_add(dev, connector, funcs, connector_type, ddc);
> >  }
> >  EXPORT_SYMBOL(drm_connector_init_with_ddc);
> >  
> > @@ -442,7 +528,7 @@ int drmm_connector_init(struct drm_device *dev,
> >  	if (drm_WARN_ON(dev, funcs && funcs->destroy))
> >  		return -EINVAL;
> >  
> > -	ret = __drm_connector_init(dev, connector, funcs, connector_type, ddc);
> > +	ret = drm_connector_init_and_add(dev, connector, funcs, connector_type, ddc);
> >  	if (ret)
> >  		return ret;
> >  
> > @@ -659,10 +745,8 @@ void drm_connector_cleanup(struct drm_connector *connector)
> >  	connector->name = NULL;
> >  	fwnode_handle_put(connector->fwnode);
> >  	connector->fwnode = NULL;
> > -	spin_lock_irq(&dev->mode_config.connector_list_lock);
> > -	list_del(&connector->head);
> > -	dev->mode_config.num_connector--;
> > -	spin_unlock_irq(&dev->mode_config.connector_list_lock);
> > +
> > +	drm_connector_remove(connector);
> >  
> >  	WARN_ON(connector->state && !connector->funcs->atomic_destroy_state);
> >  	if (connector->state && connector->funcs->atomic_destroy_state)
> > @@ -749,6 +833,32 @@ int drm_connector_register(struct drm_connector *connector)
> >  }
> >  EXPORT_SYMBOL(drm_connector_register);
> >  
> > +/**
> > + * drm_connector_dynamic_register - register a dynamic connector
> > + * @connector: the connector to register
> > + *
> > + * Register userspace interfaces for a connector. Only call this for connectors
> > + * initialized by calling drm_connector_dynamic_init(). All other connectors
> > + * will be registered automatically when calling drm_dev_register().
> > + *
> > + * When the connector is no longer available the driver must call
> > + * drm_connector_unregister().
> > + *
> > + * Returns:
> > + * Zero on success, error code on failure.
> > + */
> > +int drm_connector_dynamic_register(struct drm_connector *connector)
> > +{
> > +	/* Was the connector inited already? */
> > +	if (WARN_ON(!(connector->funcs && connector->funcs->destroy)))
> > +		return -EINVAL;
> > +
> > +	drm_connector_add(connector);
> > +
> > +	return drm_connector_register(connector);
> > +}
> > +EXPORT_SYMBOL(drm_connector_dynamic_register);
> 
> On the one hand I don't want to rehash this series anymore, but on the
> other hand... if the dynamic register set a flag, say connector->dynamic
> or whatever, we could keep the single drm_connector_register() that
> behaves slightly differently for dynamically initialized connectors.

The reason for a separate register function is that drivers should
register/unregister only a dynamic connector (MST). For that they
should use

drm_connector_dynamic_init(),
drm_connector_dynamic_register() and (eventually)
drm_connector_dynamic_unregister().

Instead of the last, drivers still use drm_connector_unregister(), but I
think that should be also changed - after more thought about the
unregister path - according to the above. This would make the API
clearer imo and would leave

drm_connector_register() / drm_connector_unregister() for DRM core's
internal use. I suppose this was also Sima's idea.

> And it could provide some extra sanity checking as well. But
> *shrug*. This works.
> 
> BR,
> Jani.
> 
> > +
> >  /**
> >   * drm_connector_unregister - unregister a connector
> >   * @connector: the connector to unregister
> > diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> > index e3fa43291f449..f766d194221d1 100644
> > --- a/include/drm/drm_connector.h
> > +++ b/include/drm/drm_connector.h
> > @@ -2126,6 +2126,11 @@ int drm_connector_init(struct drm_device *dev,
> >  		       struct drm_connector *connector,
> >  		       const struct drm_connector_funcs *funcs,
> >  		       int connector_type);
> > +int drm_connector_dynamic_init(struct drm_device *dev,
> > +			       struct drm_connector *connector,
> > +			       const struct drm_connector_funcs *funcs,
> > +			       int connector_type,
> > +			       struct i2c_adapter *ddc);
> >  int drm_connector_init_with_ddc(struct drm_device *dev,
> >  				struct drm_connector *connector,
> >  				const struct drm_connector_funcs *funcs,
> > @@ -2147,6 +2152,7 @@ int drmm_connector_hdmi_init(struct drm_device *dev,
> >  			     unsigned int max_bpc);
> >  void drm_connector_attach_edid_property(struct drm_connector *connector);
> >  int drm_connector_register(struct drm_connector *connector);
> > +int drm_connector_dynamic_register(struct drm_connector *connector);
> >  void drm_connector_unregister(struct drm_connector *connector);
> >  int drm_connector_attach_encoder(struct drm_connector *connector,
> >  				      struct drm_encoder *encoder);
> 
> -- 
> Jani Nikula, Intel