[PATCH] drm/dp/mst: Restore primary hub guid on resume

[Harry Wentland]

Patch makes sense to me. It looks like when the receiver detects an 
upstream disconnect it will reset its internal state, at least somewhat. 
We've seen that happen when system enters S3 and GPU loses power.

Reviewed-by: Harry Wentland <harry.wentland at amd.com>

Harry

On 2016-04-13 04:50 PM, Lyude wrote:
> Some hubs are forgetful, and end up forgetting whatever GUID we set
> previously after we do a suspend/resume cycle. This can lead to
> hotplugging breaking (along with probably other things) since the hub
> will start sending connection notifications with the wrong GUID. As
> such, we need to check on resume whether or not the GUID the hub is
> giving us is valid.
>
> Signed-off-by: Lyude <cpaul at redhat.com>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
> ---
>   drivers/gpu/drm/drm_dp_mst_topology.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 27fbd79..d2efd78 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2121,6 +2121,8 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr)
>   
>   	if (mgr->mst_primary) {
>   		int sret;
> +		u8 guid[16];
> +
>   		sret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
>   		if (sret != DP_RECEIVER_CAP_SIZE) {
>   			DRM_DEBUG_KMS("dpcd read failed - undocked during suspend?\n");
> @@ -2135,6 +2137,16 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr)
>   			ret = -1;
>   			goto out_unlock;
>   		}
> +
> +		/* Some hubs forget their guids after they resume */
> +		sret = drm_dp_dpcd_read(mgr->aux, DP_GUID, guid, 16);
> +		if (sret != 16) {
> +			DRM_DEBUG_KMS("dpcd read failed - undocked during suspend?\n");
> +			ret = -1;
> +			goto out_unlock;
> +		}
> +		drm_dp_check_mstb_guid(mgr->mst_primary, guid);
> +
>   		ret = 0;
>   	} else
>   		ret = -1;