[PATCH 1/2] drm/dp_mst: Add a function to determine the mst end device

[Lyude Paul]

This patch series looks awesome so far, thank you for the great work! This
patch looks great, I think we should just squash it into the next patch though
since we don't use this function until then.

On Wed, 2020-01-08 at 16:44 +0800, Wayne Lin wrote:
> [Why]
> For later usage convenience, add the function
> drm_dp_mst_is_dp_mst_end_device() to decide whether a peer device
> connected to a DFP is mst end device. Which also indicates if the peer
> device is capable of handling message or not.
> 
> Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index eebf325d7f48..8f54b241db08 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -1918,6 +1918,22 @@ static u8 drm_dp_calculate_rad(struct drm_dp_mst_port
> *port,
>  	return parent_lct + 1;
>  }
>  
> +static bool drm_dp_mst_is_dp_mst_end_device(u8 pdt, bool mcs)
> +{
> +	switch (pdt) {
> +	case DP_PEER_DEVICE_DP_LEGACY_CONV:
> +	case DP_PEER_DEVICE_SST_SINK:
> +		return true;
> +	case DP_PEER_DEVICE_MST_BRANCHING:
> +		/* For sst branch device */
> +		if (!mcs)
> +			return true;
> +
> +		return false;
> +	}
> +	return true;
> +}
> +
>  static int drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt)
>  {
>  	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
-- 
Cheers,
	Lyude Paul