[PATCH] V2: Currently, DRM get the capability of the mst hub only from DP_DPCD_REV and get the slower speed even the mst hub can run in the faster speed.

[Lyude Paul]

The commit message should be shorter and follow the format other commits for
drm usually do, in this case something like:

drm/dp_mst: Retrieve extended DPCD caps for topology manager

On Thu, 2020-09-10 at 14:36 +0800, Koba Ko wrote:
> As per DP-1.3, First check DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT.
> If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 1, read the DP_DP13_DPCD_REV to
> get the faster capability.
> If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 0, read DP_DPCD_REV.
> 
> Signed-off-by: Koba Ko <koba.ko at canonical.com>
> ---
> ChangeLog:
> 1. use drm_dp_read_dpcd_caps instead.
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 7753c718ddf9..293f71d0ae90 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3694,8 +3694,8 @@ int drm_dp_mst_topology_mgr_set_mst(struct
> drm_dp_mst_topology_mgr *mgr, bool ms
>  			((dpcd_ext & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT)
> ?  DP_DP13_DPCD_REV : DP_DPCD_REV);
>  
>  		/* get dpcd info */
> -		ret = drm_dp_dpcd_read(mgr->aux, dpcd_offset, mgr->dpcd,
> DP_RECEIVER_CAP_SIZE);
> -		if (ret != DP_RECEIVER_CAP_SIZE) {
> +		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
> +		if (ret < 0) {
>  			DRM_DEBUG_KMS("failed to read DPCD\n");

Let's use drm_dbg_kms() here, and let's also print the return code when this
fails.

With those things fixed:

Reviewed-by: Lyude Paul <lyude at redhat.com>

>  			goto out_unlock;
>  		}
-- 
Cheers,
	Lyude Paul (she/her)
	Software Engineer at Red Hat