[PATCH] drm/dp_mst: clear time slots for ports invalid
Lyude Paul
lyude at redhat.com
Fri Jan 3 23:33:50 UTC 2020
On Wed, 2019-12-25 at 06:45 +0000, Lin, Wayne wrote:
> > -----Original Message-----
> > From: Lyude Paul <lyude at redhat.com>
> > Sent: Saturday, December 21, 2019 8:12 AM
> > To: Lin, Wayne <Wayne.Lin at amd.com>; dri-devel at lists.freedesktop.org;
> > amd-gfx at lists.freedesktop.org
> > Cc: Kazlauskas, Nicholas <Nicholas.Kazlauskas at amd.com>; Wentland, Harry
> > <Harry.Wentland at amd.com>; Zuo, Jerry <Jerry.Zuo at amd.com>;
> > stable at vger.kernel.org
> > Subject: Re: [PATCH] drm/dp_mst: clear time slots for ports invalid
> >
> > Mhh-I think I understand the problem you're trying to solve here but I
> > think this
> > solution might be a bit overkill. When I did the rework of topology
> > references
> > for ports, I made it so that we can guarantee memory access to a port
> > without
> > it needing to be a valid part of the topology. As well, all parents of the
> > port are
> > guaranteed to be accessible for as long as the child is. Take a look at:
> >
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2F01.org%
> > 2Flinuxgraphics%2Fgfx-docs%2Fdrm%2Fgpu%2Fdrm-kms-helpers.html%23refco
> > unt-relationships-in-a-topology&data=02%7C01%7Cwayne.lin%40amd.co
> > m%7C722655b546c049dc081908d785aa6758%7C3dd8961fe4884e608e11a82d
> > 994e183d%7C0%7C0%7C637124839257213115&sdata=Ctha3ja8kleeFOp
> > PpA7EwDV1is81RAMsjqd1P6463ak%3D&reserved=0
> >
> > It's also worth noting that because of this there's a lot of
> > get_port_validated()/put_port_validated() calls in the MST helpers that
> > are
> > now bogus and need to be removed once I get a chance. For new code we
> > should limit the use of topology references to sections of code where we
> > need
> > a guarantee that resources on the port/branch (such as a drm connector, dp
> > aux port, etc.) won't go away for as long as we need to use them.
> >
> > Do you think we could change this patch so instead of removing it from the
> > proposed payloads on the CONNECTION_STATUS_NOTIFY, we keep the port's
> > memory allocation around until it's been removed from the proposed
> > payloads
> > table and clean it up there on the next payload update?
> >
> Really appreciate for your time and comments in detail.
>
> In this patch, I wanted to just set the proposed_vcpi->num_slots to 0 for
> those
> ports which are no longer in the topology due to there is no need to
> allocate time
> slots for these port. And expect those vcpi will be updated during next
> update of
> payload ID table by drm_dp_update_payload_part1().
>
> I tried to use drm_dp_mst_topology_get_port_validated() as a helper to
> decide whether a port is in the topology or not. Use this function to
> iterate over
> all ports that all proposed_vcpi[] drive to. If one port is not in the
> topology, set the
> num_slots of the proposed_vcpi for this port to 0. With num_slots as 0,
> these
> proposed_vcpi will be clean up in next payload table update by
> drm_dp_update_payload_part1(). If a port is still in the topology, then
> release
> the reference count which was acquired previously from
> drm_dp_mst_topology_get_port_validated() and do nothing.
>
> I didn't mean to kill invalid ports on receiving CONNECTION_STATUS_NOTIFY.
> Sorry if I misuse or misunderstand something here?
Ahh, it seems I made the mistake here then because from your explanation
you're using the API exactly as intended :). All of this has me wondering if
some day we should try to get rid of the payload tracking we have and move it
into atomic. But, that's a problem for another day.
Anyway-one small change below:
>
> > On Fri, 2019-12-06 at 16:39 +0800, Wayne Lin wrote:
> > > [Why]
> > > When change the connection status in a MST topology, mst device which
> > > detect the event will send out CONNECTION_STATUS_NOTIFY messgae.
> > >
> > > e.g. src-mst-mst-sst => src-mst (unplug) mst-sst
> > >
> > > Currently, under the above case of unplugging device, ports which have
> > > been allocated payloads and are no longer in the topology still occupy
> > > time slots and recorded in proposed_vcpi[] of topology manager.
> > >
> > > If we don't clean up the proposed_vcpi[], when code flow goes to try
> > > to update payload table by calling drm_dp_update_payload_part1(), we
> > > will fail at checking port validation due to there are ports with
> > > proposed time slots but no longer in the mst topology. As the result
> > > of that, we will also stop updating the DPCD payload table of down
> > > stream
> > port.
> > > [How]
> > > While handling the CONNECTION_STATUS_NOTIFY message, add a detection
> > > to see if the event indicates that a device is unplugged to an output
> > > port.
> > > If the detection is true, then iterrate over all proposed_vcpi[] to
> > > see whether a port of the proposed_vcpi[] is still in the topology or
> > > not. If the port is invalid, set its num_slots to 0.
> > >
> > > Thereafter, when try to update payload table by calling
> > > drm_dp_update_payload_part1(), we can successfully update the DPCD
> > > payload table of down stream port and clear the proposed_vcpi[] to NULL.
> > >
> > > Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
> > > Cc: stable at vger.kernel.org
> > > ---
> > > drivers/gpu/drm/drm_dp_mst_topology.c | 24
> > +++++++++++++++++++++++-
> > > 1 file changed, 23 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 5306c47dc820..2e236b6275c4 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -2318,7 +2318,7 @@ drm_dp_mst_handle_conn_stat(struct
> > > drm_dp_mst_branch *mstb, {
> > > struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> > > struct drm_dp_mst_port *port;
> > > - int old_ddps, ret;
> > > + int old_ddps, old_input, ret, i;
> > > u8 new_pdt;
> > > bool dowork = false, create_connector = false;
> > >
> > > @@ -2349,6 +2349,7 @@ drm_dp_mst_handle_conn_stat(struct
> > > drm_dp_mst_branch *mstb,
> > > }
> > >
> > > old_ddps = port->ddps;
> > > + old_input = port->input;
> > > port->input = conn_stat->input_port;
> > > port->mcs = conn_stat->message_capability_status;
> > > port->ldps = conn_stat->legacy_device_plug_status;
> > > @@ -2373,6 +2374,27 @@ drm_dp_mst_handle_conn_stat(struct
> > > drm_dp_mst_branch *mstb,
> > > dowork = false;
> > > }
> > >
> > > + if (!old_input && old_ddps != port->ddps && !port->ddps) {
> > > + for (i = 0; i < mgr->max_payloads; i++) {
> > > + struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
> > > + struct drm_dp_mst_port *port_validated;
> > > +
> > > + if (vcpi) {
Let's invert this conditional to reduce the indenting here a bit
if (!vcpi)
continue;
With that change this is:
Reviewed-by: Lyude Paul <lyude at redhat.com>
> > > + port_validated =
> > > + container_of(vcpi, struct
> > > drm_dp_mst_port, vcpi);
> > > + port_validated =
> > > + drm_dp_mst_topology_get_port_validated
> > > (mgr, port_validated);
> > > + if (!port_validated) {
> > > + mutex_lock(&mgr->payload_lock);
> > > + vcpi->num_slots = 0;
> > > + mutex_unlock(&mgr->payload_lock);
> > > + } else {
> > > + drm_dp_mst_topology_put_port(port_vali
> > > dated);
> > > + }
> > > + }
> > > + }
> > > + }
> > > +
> > > if (port->connector)
> > > drm_modeset_unlock(&mgr->base.lock);
> > > else if (create_connector)
> > --
> > Cheers,
> > Lyude Paul
> --
> Best regards,
> Wayne Lin
--
Cheers,
Lyude Paul
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