On Tue, 2020-10-20 at 16:25 -0700, José Roberto de Souza wrote:
> On Tue, 2020-10-20 at 15:41 +0300, Ville Syrjälä wrote:
> > On Tue, Oct 20, 2020 at 12:45:55AM -0700, Khaled Almahallawy wrote:
> > > This patch avoids failing atomic commits sent by user space by making
> > > sure CRTC/Connector added to drm_atomic_state by the driver are in valid
> > > state.
> > >
> > > When disconnecting MST hub with two or more connected displays. The user
> > > space sends IOCTL for each MST pipe to disable.
> > > drm_atomic_state object sent from user space contains only the state of
> > > the crtc/pipe intended to disable.
> > > In TGL, intel_dp_mst_atomic_master_trans_check will add all other CRTC
> > > and connectors that share the MST stream to drm_atomic_state:
> > >
> > > drm_atomic_commit
> > > drm_atomic_helper_check_modeset
> > > update_connector_routing
> > > intel_dp_mst_atomic_check = funcs->atomic_check(connector, state);
> > > intel_dp_mst_atomic_master_trans_check
> > > intel_atomic_get_digital_connector_state
> > > drm_atomic_get_connector_state <-- Add all Connectors
> > > drm_atomic_get_crtc_state <-- Add all CRTCs
> > > update_connector_routing <-- Check added Connector/CRTCs - Will
> > > fail
> > >
> > > However the added crtc/connector pair will be in invalid state (enabled
> > > state for a removed connector)
> > > triggering this condition in drm_atomic_helper.c/update_connector_routing:
> > >
> > > if (!state->duplicated && drm_connector_is_unregistered(connector) &&
> > > crtc_state->active) {
> > > DRM_DEBUG_ATOMIC("[CONNECTOR:%d:%s] is not registered\n",
> > > connector->base.id, connector->name);
> > > return -EINVAL;
> > > }
> >
> > Yeah, I think that "reject modeset on unregistered connectors" idea is
> > a bit broken given how the uapi has worked in the past. Cc:ing danvet
> > and lyude who IIRC were involved with that.
> >
> > Hmm. Maybe we could add the other stuff to the state only after the
> > connector .atomic_check() stuff has been done? I don't quite remember
> > why we decided to do it here. José do you recall the details?
>
> Because the connector check function runs twice in
> drm_atomic_helper_check_modeset(), in the first iteration it will add all
> connectors that share the
> same MST stream to state, the second one will make sure all other checks
> passed in all connectors of the MST stream.
>
> To me looks like the Chrome userspace is not doing the right thing, it is
> sending asynchronous atomic commits with conflicting state between each
> commit.
Oh it do not have information about other connectors so not conflicting but
anyways userspace should retry atomic commits anyways.
> If it had a pool that dispatch one atomic state at time waiting for
> completion before dispatch the next one it would not be a issue.
>
> >
> > >
> > > Which will cause the drm_atomic_commit/IOCTL for disabling one of MST
> > > stream pipes (Main MST) to fail.
> > >
> > > The problem happens when a user space (as Chrome) doesn’t retry a falling
> > > commit, leaving a disconnected MST pipe still ON,
> > > which will result in failing reconnect of MST hub or even worse leaving
> > > TC PHY in a connected state while the MST Hub is disconnected.
> > >
> > > Tested on Ubuntu(drm-tip) and Chrome(kernel-next 5.9 rc7)
> > >
> > > Signed-off-by: Khaled Almahallawy <khaled.almahall...@intel.com>
> > > ---
> > > drivers/gpu/drm/i915/display/intel_dp_mst.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > index e948aacbd4ab..1ede980876ed 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > > @@ -265,6 +265,9 @@ intel_dp_mst_atomic_master_trans_check(struct
> > > intel_connector *connector,
> > > return ret;
> > > }
> > > crtc_state->uapi.mode_changed = true;
> > > +
> > > + if (connector_iter->base.status ==
> > > connector_status_disconnected)
> > > + crtc_state->uapi.active = false;
> >
> > That will make the state userspace last set inconsistent with what's
> > really going on. Which means suddenly page flips/vblank waits and
> > whatnot will start to fail.
> >
> > Also that wil directly mutate the prop visible to user space, which
> > is not how these things are supposed to work. I think if we did do
> > something like this we should maybe have some kind of internal
> > flag for it.
> >
> > > }
> > > drm_connector_list_iter_end(&connector_list_iter);
> > >
> > >
> > >
> > >
> > > --
> > > 2.25.1
> >
>
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