[Intel-gfx] [PATCH] drm/dp/mst: Read the extended DPCD capabilities during system resume

[Imre Deak]

On Tue, Jun 14, 2022 at 03:32:59PM +0300, Jani Nikula wrote:
> On Tue, 14 Jun 2022, Imre Deak <imre.deak at intel.com> wrote:
> > The WD22TB4 Thunderbolt dock at least will revert its DP_MAX_LINK_RATE
> > from HBR3 to HBR2 after system suspend/resume if the DP_DP13_DPCD_REV
> > registers are not read subsequently also as required.
> 
> Does it actually change the behaviour depending on whether the dpcd is
> read or not, or is this just about the resume path overwriting mgr->dpcd
> with stuff from DP_DPCD_REV?

Yes, the reading out DP_DP13_DPCD_REV has a side-effect, see
https://gitlab.freedesktop.org/drm/intel/-/issues/5292#note_1343399

> drm_dp_mst_topology_mgr_set_mst() does use drm_dp_read_dpcd_caps() for
> reading the caps, which would normally set mgr->dpcd from
> DP_DP13_DPCD_REV.

Right, but at that point DP_DP13_DPCD_REV returns HBR2 w/o this change.

> BR,
> Jani.
> 
> >
> > Fix this by reading DP_DP13_DPCD_REV registers as well, matching what is
> > done during connector detection. While at it also fix up the same call
> > in drm_dp_mst_dump_topology().
> >
> > Cc: Lyude Paul <lyude at redhat.com>
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5292
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/display/drm_dp_mst_topology.c | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > index 67b3b9697da7f..18f2b6075b780 100644
> > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > @@ -3860,9 +3860,7 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr,
> >  	if (!mgr->mst_primary)
> >  		goto out_fail;
> >  
> > -	ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd,
> > -			       DP_RECEIVER_CAP_SIZE);
> > -	if (ret != DP_RECEIVER_CAP_SIZE) {
> > +	if (drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd) < 0) {
> >  		drm_dbg_kms(mgr->dev, "dpcd read failed - undocked during suspend?\n");
> >  		goto out_fail;
> >  	}
> > @@ -4911,8 +4909,7 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
> >  		u8 buf[DP_PAYLOAD_TABLE_SIZE];
> >  		int ret;
> >  
> > -		ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, buf, DP_RECEIVER_CAP_SIZE);
> > -		if (ret) {
> > +		if (drm_dp_read_dpcd_caps(mgr->aux, buf) < 0) {
> >  			seq_printf(m, "dpcd read failed\n");
> >  			goto out;
> >  		}
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center