We just added a new helper for DPCD retrieval to drm_dp_helper.c (which also
handles grabbing the extended receiver caps), we should probably make use of
it here
On Wed, 2020-09-09 at 14:31 +0800, Koba Ko wrote:
> On Thu, Aug 27, 2020 at 1:30 PM Koba Ko <koba.ko@xxxxxxxxxxxxx> 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.ko@xxxxxxxxxxxxx>
> > ---
> > 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
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
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