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    Subject[PATCH 4.4 075/163] drm/dp/mst: Restore primary hub guid on resume
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Lyude <cpaul@redhat.com>

    commit 9dc0487d96a0396367a1451b31873482080b527f upstream.

    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@redhat.com>
    Reviewed-by: Harry Wentland <harry.wentland@amd.com>
    Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Link: http://patchwork.freedesktop.org/patch/msgid/1460580618-7421-1-git-send-email-cpaul@redhat.com
    Signed-off-by: Dave Airlie <airlied@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -2116,6 +2116,8 @@ int drm_dp_mst_topology_mgr_resume(struc

    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");
    @@ -2130,6 +2132,16 @@ int drm_dp_mst_topology_mgr_resume(struc
    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;

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