On Thu, Aug 22, 2024 at 05:53:19PM +0300, Jani Nikula wrote: > On Thu, 22 Aug 2024, Imre Deak <imre.deak@xxxxxxxxx> wrote: > > On Thu, Aug 22, 2024 at 01:00:03PM +0300, Jani Nikula wrote: > >> On Wed, 21 Aug 2024, Imre Deak <imre.deak@xxxxxxxxx> wrote: > >> > On Wed, Aug 21, 2024 at 05:19:11PM +0300, Jani Nikula wrote: > >> >> On Wed, 24 Jul 2024, Imre Deak <imre.deak@xxxxxxxxx> wrote: > >> >> > In some cases the sink can reset itself after it was configured into MST > >> >> > mode, without the driver noticing the disconnected state. For instance > >> >> > the reset may happen in the middle of a modeset, or the (long) HPD pulse > >> >> > generated may be not long enough for the encoder detect handler to > >> >> > observe the HPD's deasserted state. In this case the sink's DPCD > >> >> > register programmed to enable MST will be reset, while the driver still > >> >> > assumes MST is still enabled. Detect this condition, which will tear > >> >> > down and recreate/re-enable the MST topology. > >> >> > > >> >> > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11195 > >> >> > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > >> >> > --- > >> >> > drivers/gpu/drm/i915/display/intel_dp.c | 3 +++ > >> >> > drivers/gpu/drm/i915/display/intel_dp_mst.c | 30 +++++++++++++++++++++ > >> >> > drivers/gpu/drm/i915/display/intel_dp_mst.h | 1 + > >> >> > 3 files changed, 34 insertions(+) > >> >> > > >> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c > >> >> > index 1e43e32e05199..c621f6daf8235 100644 > >> >> > --- a/drivers/gpu/drm/i915/display/intel_dp.c > >> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c > >> >> > @@ -5878,6 +5878,9 @@ intel_dp_detect(struct drm_connector *connector, > >> >> > else > >> >> > status = connector_status_disconnected; > >> >> > > >> >> > + if (!intel_dp_mst_verify_dpcd_state(intel_dp)) > >> >> > + status = connector_status_disconnected; > >> >> > + > >> >> > >> >> So I still don't understand. We've got a detect which we've determined > >> >> is connected. But then we disconnect because the sink state has changed. > >> >> > >> >> How do we get another connect? > >> > > >> > The detect in this case will be retried with a 1 sec delay, since the > >> > mode changes back to SST and the connector state stays disconnected. > >> > >> What exactly triggers the retry? I don't see this triggering the > >> INTEL_HOTPLUG_RETRY case. > > > > drm_connector::status is connector_status_disconnected before the detect > > (as always for an MST root connector) > > This was one of the missing pieces for me. I just thought we'd get here > with connector_status_connected && is_mst == true, which would lead to a > change. Yes, what the connector status means for an MST root connector is not very clear. How the detect will get retried also needs a comment here I think, I'll add that. > Very well then. One final nitpick below. > > > and it stays > > connector_status_disconnected. The connector's mode will also change to > > SST (intel_dp::is_mst from true to false). This condition will lead to > > the detect getting retried. > > > > A detect will actually happen in any case, since removing the MST > > connectors results in a (global) hotplug uevent being sent, to which > > userspace should respond with re-probing all connectors. > > > >> I'm just trying to understand, please bear with me. > >> [...] > >> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c > >> >> > index 27ce5c3f5951e..89b147e37b400 100644 > >> >> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c > >> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c > >> >> > @@ -1998,3 +1998,33 @@ bool intel_dp_mst_crtc_needs_modeset(struct intel_atomic_state *state, > >> >> > > >> >> > return false; > >> >> > } > >> >> > + > >> >> > +/** > >> >> > + * intel_dp_mst_verify_dpcd_state - verify the MST SW enabled state wrt. the DPCD > >> >> > + * @intel_dp: DP port object > >> >> > + * > >> >> > + * Verify if @intel_dp's MST enabled SW state matches the corresponding DPCD > >> >> > + * state. A long HPD pulse -not long enough to be detected as a disconnected > >> >> > + * state - could've reset the DPCD state, which requires tearing > >> >> > + * down/recreating the MST topology. > >> >> > + * > >> >> > + * Returns %true if the SW MST enabled and DPCD states match, %false > >> >> > + * otherwise. > >> >> > + */ > >> >> > +bool intel_dp_mst_verify_dpcd_state(struct intel_dp *intel_dp) > >> >> > +{ > >> >> > + int ret; > >> >> > + u8 val; > >> >> > + > >> >> > + if (!intel_dp->is_mst) > >> >> > + return true; > >> >> > + > >> >> > + ret = drm_dp_dpcd_readb(intel_dp->mst_mgr.aux, DP_MSTM_CTRL, &val); > >> >> > + if (ret < 0) > >> >> > + return false; > >> >> > + > >> >> > + if (val != (DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC)) > > Maybe let's add drm_dbg_kms() here so we know what's going on? Ok, can add it. > > BR, > Jani. > > > >> >> > + return false; > >> >> > + > >> >> > + return true; > >> >> > +} > >> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.h b/drivers/gpu/drm/i915/display/intel_dp_mst.h > >> >> > index 8ca1d599091c6..9e4c7679f1c3a 100644 > >> >> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.h > >> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.h > >> >> > @@ -27,5 +27,6 @@ int intel_dp_mst_atomic_check_link(struct intel_atomic_state *state, > >> >> > struct intel_link_bw_limits *limits); > >> >> > bool intel_dp_mst_crtc_needs_modeset(struct intel_atomic_state *state, > >> >> > struct intel_crtc *crtc); > >> >> > +bool intel_dp_mst_verify_dpcd_state(struct intel_dp *intel_dp); > >> >> > > >> >> > #endif /* __INTEL_DP_MST_H__ */ > >> >> > >> >> -- > >> >> Jani Nikula, Intel > >> > >> -- > >> Jani Nikula, Intel > > -- > Jani Nikula, Intel
