Re: [Intel-gfx] [PATCH v1 2/2] drm/i915: Reject the atomic modeset if an associated Type-C port is disconnected

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

On Mon, May 16, 2022 at 01:54:02AM -0700, Vivek Kasireddy wrote:
> Although, doing a modeset on any disconnected connector might be futile,
> it can be particularly problematic if the connector is a Type-C port
> without a sink. And, the spec only says "Display software must not use
> a disconnected port" while referring to the Type-C DDI seqeuence, it does
> not spell out what happens if such an attempt is made. Experimental results
> have shown that this can lead to serious issues including a system hang.
> Therefore, reject the atomic modeset if we detect that the Type-C port
> is not connected.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_atomic.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_atomic.c b/drivers/gpu/drm/i915/display/intel_atomic.c
> index 40da7910f845..40576964b8c1 100644
> --- a/drivers/gpu/drm/i915/display/intel_atomic.c
> +++ b/drivers/gpu/drm/i915/display/intel_atomic.c
> @@ -114,6 +114,8 @@ int intel_digital_connector_atomic_set_property(struct drm_connector *connector,
>  int intel_digital_connector_atomic_check(struct drm_connector *conn,
>  					 struct drm_atomic_state *state)
>  {
> +	struct drm_device *dev = conn->dev;
> +	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct drm_connector_state *new_state =
>  		drm_atomic_get_new_connector_state(state, conn);
>  	struct intel_digital_connector_state *new_conn_state =
> @@ -122,6 +124,10 @@ int intel_digital_connector_atomic_check(struct drm_connector *conn,
>  		drm_atomic_get_old_connector_state(state, conn);
>  	struct intel_digital_connector_state *old_conn_state =
>  		to_intel_digital_connector_state(old_state);
> +	struct intel_encoder *encoder =
> +		intel_attached_encoder(to_intel_connector(conn));
> +	struct intel_digital_port *dig_port =
> +		encoder ? enc_to_dig_port(encoder) : NULL;
>  	struct drm_crtc_state *crtc_state;
>  
>  	intel_hdcp_atomic_check(conn, old_state, new_state);
> @@ -131,6 +137,20 @@ int intel_digital_connector_atomic_check(struct drm_connector *conn,
>  
>  	crtc_state = drm_atomic_get_new_crtc_state(state, new_state->crtc);
>  
> +	/*
> +	 * The spec says that it is not safe to use a disconnected Type-C port.
> +	 * Therefore, check to see if this connector is connected and reject
> +	 * the modeset if there is no sink detected.
> +	 */
> +	if (dig_port && !dig_port->connected(encoder) &&

This check is racy, as right after dig_port->connected() returns true,
the port can become disconnected.

> +	    intel_phy_is_tc(dev_priv,
> +	    intel_port_to_phy(dev_priv, encoder->port))) {
> +		drm_dbg_atomic(&dev_priv->drm,
> +			       "[CONNECTOR:%d:%s] is not connected; rejecting the modeset\n",
> +			       conn->base.id, conn->name);
> +		return -EINVAL;
> +	}
> +
>  	/*
>  	 * These properties are handled by fastset, and might not end
>  	 * up in a modeset.
> -- 
> 2.35.1
>