On Thu, Aug 27, 2020 at 1:30 PM Koba Ko <koba...@canonical.com> wrote:
>
> 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.
>
> 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...@canonical.com>
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 67dd72ea200e..3b84c6801281 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3497,6 +3497,8 @@ static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8
> dp_link_count)
> int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr,
> bool mst_state)
> {
> int ret = 0;
> + u8 dpcd_ext = 0;
> + unsigned int dpcd_offset = 0;
> struct drm_dp_mst_branch *mstb = NULL;
>
> mutex_lock(&mgr->payload_lock);
> @@ -3510,9 +3512,15 @@ int drm_dp_mst_topology_mgr_set_mst(struct
> drm_dp_mst_topology_mgr *mgr, bool ms
> struct drm_dp_payload reset_pay;
>
> WARN_ON(mgr->mst_primary);
> + drm_dp_dpcd_read(mgr->aux,
> + DP_TRAINING_AUX_RD_INTERVAL,
> + &dpcd_ext, sizeof(dpcd_ext));
> +
> + dpcd_offset =
> + ((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, DP_DPCD_REV, mgr->dpcd,
> DP_RECEIVER_CAP_SIZE);
> + ret = drm_dp_dpcd_read(mgr->aux, dpcd_offset, mgr->dpcd,
> DP_RECEIVER_CAP_SIZE);
> if (ret != DP_RECEIVER_CAP_SIZE) {
> DRM_DEBUG_KMS("failed to read DPCD\n");
> goto out_unlock;
> --
> 2.25.1
>
Add Lyude Paul
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