Re: [PATCH v3 4/4] drm_dp_cec: add MST support

[Hans Verkuil <hverkuil@xs4all.nl>]

On 23/09/2020 04:13, Sam McNally wrote:
> With DP v2.0 errata E5, CEC tunneling can be supported through an MST
> topology.
> 
> There are some minor differences for CEC tunneling through an MST
> topology compared to CEC tunneling to an SST port:
> - CEC IRQs are delivered via a sink event notify message
> - CEC-related DPCD registers are accessed via remote DPCD reads and
>   writes.
> 
> This results in the MST implementation diverging from the existing SST
> implementation:
> - sink event notify messages with CEC_IRQ ID set indicate CEC IRQ rather
>   than ESI1
> - setting edid and handling CEC IRQs, which can be triggered from
>   contexts where locks held preclude HPD handling, are deferred to avoid
>   remote DPCD access which would block until HPD handling is performed
>   or a timeout
> 
> Register and unregister for all MST connectors, ensuring their
> drm_dp_aux_cec struct won't be accessed uninitialized.
> 
> Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Signed-off-by: Sam McNally <sammc@chromium.org>
> ---
> 
> Changes in v3:
> - Fixed whitespace in drm_dp_cec_mst_irq_work()
> - Moved drm_dp_cec_mst_set_edid_work() with the other set_edid functions
> 
> Changes in v2:
> - Used aux->is_remote instead of aux->cec.is_mst, removing the need for
>   the previous patch in the series
> - Added a defensive check for null edid in the deferred set_edid work,
>   in case the edid is no longer valid at that point
> 
>  drivers/gpu/drm/drm_dp_cec.c          | 68 +++++++++++++++++++++++++--
>  drivers/gpu/drm/drm_dp_mst_topology.c | 24 ++++++++++
>  include/drm/drm_dp_helper.h           |  4 ++
>  3 files changed, 91 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_cec.c b/drivers/gpu/drm/drm_dp_cec.c
> index 3ab2609f9ec7..1020b2cffdf0 100644
> --- a/drivers/gpu/drm/drm_dp_cec.c
> +++ b/drivers/gpu/drm/drm_dp_cec.c
> @@ -14,6 +14,7 @@
>  #include <drm/drm_connector.h>
>  #include <drm/drm_device.h>
>  #include <drm/drm_dp_helper.h>
> +#include <drm/drm_dp_mst_helper.h>
>  
>  /*
>   * Unfortunately it turns out that we have a chicken-and-egg situation
> @@ -248,6 +249,10 @@ void drm_dp_cec_irq(struct drm_dp_aux *aux)
>  	if (!aux->transfer)
>  		return;
>  
> +	if (aux->is_remote) {
> +		schedule_work(&aux->cec.mst_irq_work);
> +		return;
> +	}

Are these workqueues for cec_irq and cec_set_edid actually needed? They are called
directly from drm_dp_mst_topology.c, and I think they can be handled identically to
a normal, non-remote, aux device.

Avoiding using a workqueue probably also means that there is no need for exporting
drm_dp_mst_topology_get_port_validated and drm_dp_mst_topology_put_port.

Provided that I am not missing something, this should simplify the code quite a bit.

Regards,

	Hans

>  	mutex_lock(&aux->cec.lock);
>  	if (!aux->cec.adap)
>  		goto unlock;
> @@ -276,6 +281,23 @@ static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
>  	return true;
>  }
>  
> +static void drm_dp_cec_mst_irq_work(struct work_struct *work)
> +{
> +	struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
> +					      cec.mst_irq_work);
> +	struct drm_dp_mst_port *port =
> +		container_of(aux, struct drm_dp_mst_port, aux);
> +
> +	port = drm_dp_mst_topology_get_port_validated(port->mgr, port);
> +	if (!port)
> +		return;
> +	mutex_lock(&aux->cec.lock);
> +	if (aux->cec.adap)
> +		drm_dp_cec_handle_irq(aux);
> +	mutex_unlock(&aux->cec.lock);
> +	drm_dp_mst_topology_put_port(port);
> +}
> +
>  /*
>   * Called if the HPD was low for more than drm_dp_cec_unregister_delay
>   * seconds. This unregisters the CEC adapter.
> @@ -297,7 +319,8 @@ static void drm_dp_cec_unregister_work(struct work_struct *work)
>   * were unchanged and just update the CEC physical address. Otherwise
>   * unregister the old CEC adapter and create a new one.
>   */
> -void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
> +static void drm_dp_cec_handle_set_edid(struct drm_dp_aux *aux,
> +				       const struct edid *edid)
>  {
>  	struct drm_connector *connector = aux->cec.connector;
>  	u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD |
> @@ -306,10 +329,6 @@ void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
>  	unsigned int num_las = 1;
>  	u8 cap;
>  
> -	/* No transfer function was set, so not a DP connector */
> -	if (!aux->transfer)
> -		return;
> -
>  #ifndef CONFIG_MEDIA_CEC_RC
>  	/*
>  	 * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
> @@ -320,6 +339,7 @@ void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
>  	 */
>  	cec_caps &= ~CEC_CAP_RC;
>  #endif
> +	cancel_work_sync(&aux->cec.mst_irq_work);
>  	cancel_delayed_work_sync(&aux->cec.unregister_work);
>  
>  	mutex_lock(&aux->cec.lock);
> @@ -375,8 +395,40 @@ void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
>  unlock:
>  	mutex_unlock(&aux->cec.lock);
>  }
> +
> +void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
> +{
> +	/* No transfer function was set, so not a DP connector */
> +	if (!aux->transfer)
> +		return;
> +
> +	if (aux->is_remote)
> +		schedule_work(&aux->cec.mst_set_edid_work);
> +	else
> +		drm_dp_cec_handle_set_edid(aux, edid);
> +}
>  EXPORT_SYMBOL(drm_dp_cec_set_edid);
>  
> +static void drm_dp_cec_mst_set_edid_work(struct work_struct *work)
> +{
> +	struct drm_dp_aux *aux =
> +		container_of(work, struct drm_dp_aux, cec.mst_set_edid_work);
> +	struct drm_dp_mst_port *port =
> +		container_of(aux, struct drm_dp_mst_port, aux);
> +	struct edid *edid = NULL;
> +
> +	port = drm_dp_mst_topology_get_port_validated(port->mgr, port);
> +	if (!port)
> +		return;
> +
> +	edid = drm_get_edid(port->connector, &port->aux.ddc);
> +
> +	if (edid)
> +		drm_dp_cec_handle_set_edid(aux, edid);
> +
> +	drm_dp_mst_topology_put_port(port);
> +}
> +
>  /*
>   * The EDID disappeared (likely because of the HPD going down).
>   */
> @@ -393,6 +445,8 @@ void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
>  		goto unlock;
>  
>  	cec_phys_addr_invalidate(aux->cec.adap);
> +	cancel_work_sync(&aux->cec.mst_irq_work);
> +
>  	/*
>  	 * We're done if we want to keep the CEC device
>  	 * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
> @@ -433,6 +487,8 @@ void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
>  	aux->cec.connector = connector;
>  	INIT_DELAYED_WORK(&aux->cec.unregister_work,
>  			  drm_dp_cec_unregister_work);
> +	INIT_WORK(&aux->cec.mst_irq_work, drm_dp_cec_mst_irq_work);
> +	INIT_WORK(&aux->cec.mst_set_edid_work, drm_dp_cec_mst_set_edid_work);
>  }
>  EXPORT_SYMBOL(drm_dp_cec_register_connector);
>  
> @@ -442,6 +498,8 @@ EXPORT_SYMBOL(drm_dp_cec_register_connector);
>   */
>  void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
>  {
> +	cancel_work_sync(&aux->cec.mst_irq_work);
> +	cancel_work_sync(&aux->cec.mst_set_edid_work);
>  	if (!aux->cec.adap)
>  		return;
>  	cancel_delayed_work_sync(&aux->cec.unregister_work);
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index c783a2a1c114..221c30133739 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2183,6 +2183,8 @@ 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)
>  {
> +	drm_dp_cec_register_connector(&port->aux, connector);
> +
>  	DRM_DEBUG_KMS("registering %s remote bus for %s\n",
>  		      port->aux.name, connector->kdev->kobj.name);
>  
> @@ -2206,6 +2208,8 @@ void drm_dp_mst_connector_early_unregister(struct drm_connector *connector,
>  	DRM_DEBUG_KMS("unregistering %s remote bus for %s\n",
>  		      port->aux.name, connector->kdev->kobj.name);
>  	drm_dp_aux_unregister_devnode(&port->aux);
> +
> +	drm_dp_cec_unregister_connector(&port->aux);
>  }
>  EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);
>  
> @@ -2515,6 +2519,21 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
>  		queue_work(system_long_wq, &mstb->mgr->work);
>  }
>  
> +static void
> +drm_dp_mst_handle_sink_event(struct drm_dp_mst_branch *mstb,
> +			    struct drm_dp_sink_event_notify *sink_event)
> +{
> +	struct drm_dp_mst_port *port;
> +
> +	if (sink_event->event_id & DP_SINK_EVENT_CEC_IRQ_EVENT) {
> +		port = drm_dp_get_port(mstb, sink_event->port_number);
> +		if (port) {
> +			drm_dp_cec_irq(&port->aux);
> +			drm_dp_mst_topology_put_port(port);
> +		}
> +	}
> +}
> +
>  static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
>  							       u8 lct, u8 *rad)
>  {
> @@ -3954,6 +3973,8 @@ drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr,
>  	if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) {
>  		drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat);
>  		hotplug = true;
> +	} else if (msg->req_type == DP_SINK_EVENT_NOTIFY) {
> +		drm_dp_mst_handle_sink_event(mstb, &msg->u.sink_event);
>  	}
>  
>  	drm_dp_mst_topology_put_mstb(mstb);
> @@ -4147,6 +4168,8 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
>  		break;
>  	}
>  out:
> +	if (ret != connector_status_connected)
> +		drm_dp_cec_unset_edid(&port->aux);
>  	drm_dp_mst_topology_put_port(port);
>  	return ret;
>  }
> @@ -4177,6 +4200,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
>  		edid = drm_get_edid(connector, &port->aux.ddc);
>  	}
>  	port->has_audio = drm_detect_monitor_audio(edid);
> +	drm_dp_cec_set_edid(&port->aux, edid);
>  	drm_dp_mst_topology_put_port(port);
>  	return edid;
>  }
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 85513eeb2196..d8ee24a6319c 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1496,12 +1496,16 @@ struct drm_connector;
>   * @adap: the CEC adapter for CEC-Tunneling-over-AUX support.
>   * @connector: the connector this CEC adapter is associated with
>   * @unregister_work: unregister the CEC adapter
> + * @mst_irq_work: IRQ for CEC events on an MST branch
> + * @mst_set_edid_work: set the EDID for an MST branch
>   */
>  struct drm_dp_aux_cec {
>  	struct mutex lock;
>  	struct cec_adapter *adap;
>  	struct drm_connector *connector;
>  	struct delayed_work unregister_work;
> +	struct work_struct mst_irq_work;
> +	struct work_struct mst_set_edid_work;
>  };
>  
>  /**
>