[PATCH 2/4] drm/dp: Add a way to init/add a connector in separate steps

[Jani Nikula]

On Fri, 15 Nov 2024, Imre Deak <imre.deak at 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 user space, which will see the connector only after it's registered
> later, it could be a problem for in-kernel users looking up connectors
> via the above list.
>
> To resolve the above issue, add a way to separately initialize the DRM
> core specific parts of the connector and add it to the above list. This
> will move adding the connector to the list after the properties on the
> connector have been added, this is ok since these steps don't have a
> dependency.
>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c | 103 ++++++++++++++++++++++++++------
>  include/drm/drm_connector.h     |   5 ++
>  2 files changed, 91 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index fc35f47e2849e..6132a7917b20c 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_core(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);
>  	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 +325,84 @@ static int __drm_connector_init(struct drm_device *dev,
>  	return ret;
>  }
>  
> +/**
> + * drm_connector_init_core - Initialize the core state of a preallocated connector
> + * @dev: DRM device
> + * @connector: the connector to init
> + * @funcs: callbacks for this connector
> + * @connector_type: user visible type of the connector
> + *
> + * Initialises the core state of preallocated connector. This is
> + * equivalent to drm_connector_init(), without adding the connector to
> + * drm_mode_config::connector_list. This call must be followed by calling
> + * drm_connector_add() during initialization to expose the connector to
> + * in-kernel users via the above list.
> + *
> + * Returns:
> + * Zero on success, error code on failure.
> + */
> +int drm_connector_init_core(struct drm_device *dev,
> +			    struct drm_connector *connector,
> +			    const struct drm_connector_funcs *funcs,
> +			    int connector_type)

Please include the ddc parameter here, and have callers pass NULL. We
absolutely don't want to see drm_connector_init_core_with_ddc().

> +{
> +	if (drm_WARN_ON(dev, !(funcs && funcs->destroy)))
> +		return -EINVAL;
> +
> +	return __drm_connector_init_core(dev, connector, funcs, connector_type, NULL);
> +}
> +EXPORT_SYMBOL(drm_connector_init_core);
> +
> +/**
> + * drm_connector_add - Add the connector
> + * @connector: the connector to add
> + *
> + * Add the connector to the drm_mode_config::connector_list, exposing the
> + * connector to in-kernel users. This call must be preceded by a call to
> + * drm_connector_init_core().
> + */
> +void drm_connector_add(struct drm_connector *connector)
> +{
> +	struct drm_device *dev = connector->dev;
> +	struct drm_mode_config *config = &dev->mode_config;
> +
> +	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);
> +}
> +EXPORT_SYMBOL(drm_connector_add);
> +
> +static void drm_connector_remove(struct drm_connector *connector)
> +{
> +	struct drm_device *dev = connector->dev;
> +
> +	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);
> +}
> +
> +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)

I'd nuke this wrapper altogether, and put the stuff inline.

Which kind of highlights that drmm_connector_init() still has the same
problem, everyone's encouraged to move towards that, but then what?

> +{
> +	int ret;
> +
> +	ret = __drm_connector_init_core(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
> @@ -659,10 +730,8 @@ 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)
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index e3fa43291f449..8e8d130b40f98 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -2122,6 +2122,11 @@ struct drm_connector {
>  
>  #define obj_to_connector(x) container_of(x, struct drm_connector, base)
>  
> +int drm_connector_init_core(struct drm_device *dev,
> +			    struct drm_connector *connector,
> +			    const struct drm_connector_funcs *funcs,
> +			    int connector_type);
> +void drm_connector_add(struct drm_connector *connector);
>  int drm_connector_init(struct drm_device *dev,
>  		       struct drm_connector *connector,
>  		       const struct drm_connector_funcs *funcs,

-- 
Jani Nikula, Intel