Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
final correction: I probably could actually get rid of this patch and do this
a bit more nicely by just making sure that we reprobe path resources for
connectors while under drm_dp_mst_topology_mgr->base.lock on CSNs, instead of
punting it off to the link address work like we seem to be doing. So, going to
try doing that instead.
On Fri, 2020-03-06 at 15:03 -0500, Lyude Paul wrote:
> On Thu, 2020-03-05 at 20:29 +0200, Ville Syrjälä wrote:
> > On Thu, Mar 05, 2020 at 01:13:36PM -0500, Lyude Paul wrote:
> > > On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> > > > On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > > > > It's next to impossible for us to do connector probing on topologies
> > > > > without occasionally racing with userspace, since creating a
> > > > > connector
> > > > > itself causes a hotplug event which we have to send before probing
> > > > > the
> > > > > available PBN of a connector. Even if we didn't have this hotplug
> > > > > event
> > > > > sent, there's still always a chance that userspace started probing
> > > > > connectors before we finished probing the topology.
> > > > >
> > > > > This can be a problem when validating a new MST state since the
> > > > > connector will be shown as connected briefly, but without any
> > > > > available
> > > > > PBN - causing any atomic state which would enable said connector to
> > > > > fail
> > > > > with -ENOSPC. So, let's simply workaround this by telling userspace
> > > > > new
> > > > > MST connectors are disconnected until we've finished probing their
> > > > > PBN.
> > > > > Since we always send a hotplug event at the end of the link address
> > > > > probing process, userspace will still know to reprobe the connector
> > > > > when
> > > > > we're ready.
> > > > >
> > > > > Signed-off-by: Lyude Paul
> > > > > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to
> > > > > MST
> > > > > atomic check")
> > > > > Cc: Mikita Lipski
> > > > > Cc: Alex Deucher
> > > > > Cc: Sean Paul
> > > > > Cc: Hans de Goede
> > > > > ---
> > > > > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > > > > 1 file changed, 13 insertions(+)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > index 207eef08d12c..7b0ff0cff954 100644
> > > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > > > > *connector,
> > > > > ret = connector_status_connected;
> > > > > break;
> > > > > }
> > > > > +
> > > > > + /* We don't want to tell userspace the port is actually
> > > > > plugged into
> > > > > + * anything until we've finished probing it's available_pbn,
> > > > > otherwise
> > > >
> > > > "its"
> > > >
> > > > Why is the connector even registered before we've finished the probe?
> > > >
> > > Oops, I'm not sure how I did this by accident but the explanation I gave
> > > in
> > > the commit message was uh, completely wrong. I must have forgotten that
> > > I
> > > made
> > > sure we didn't expose connectors before probing their PBN back when I
> > > started
> > > my MST cleanup
> > >
> > > So: despite what I said before it's not actually when new connectors are
> > > created, it's when downstream hotplugs happen which means that the
> > > conenctor's
> > > always going to be there before we probe the available_pbn.
> >
> > Not sure I understand. You're saying this is going to change for already
> > existing connectors when something else gets plugged in, and either we
> > zero it out during the probe or it always was zero to begin with for
> > whatever reason?
>
> ok-me and Sean Paul did some playing around with available_pbn and full_pbn
> (I'll get into this one in a moment), and I also played around with a couple
> of different hubs and have a much better understanding of how this should
> work
> now.
>
> So: first off tl;dr available_pbn is absolutely not what we want in
> basically
> any scenario, we actually want to use the full_pbn field that we get when
> sending ENUM_PATH_RESOURCES. Second, full_pbn represents the _smallest_
> bandwidth limitation encountered in the path between the root MSTB and each
> connected sink. Remember that there's technically a DisplayPort link trained
> between each branch device going down the topology, so that bandwidth
> limitation basically equates to "what is the lowest trained link rate that
> exists down the path to this port?". This also means that full_pbn will
> potentially change every time a new connector is plugged in, as some hubs
> will be clever and optimize the link rate they decide to use. Likewise,
> since there's not going to be anything trained on a disconnected port (e.g.
> ddps=0) there's no point in keeping full_pbn around for disconnected ports,
> since otherwise we might let users
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Thu, 2020-03-05 at 20:29 +0200, Ville Syrjälä wrote:
> On Thu, Mar 05, 2020 at 01:13:36PM -0500, Lyude Paul wrote:
> > On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> > > On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > > > It's next to impossible for us to do connector probing on topologies
> > > > without occasionally racing with userspace, since creating a connector
> > > > itself causes a hotplug event which we have to send before probing the
> > > > available PBN of a connector. Even if we didn't have this hotplug
> > > > event
> > > > sent, there's still always a chance that userspace started probing
> > > > connectors before we finished probing the topology.
> > > >
> > > > This can be a problem when validating a new MST state since the
> > > > connector will be shown as connected briefly, but without any
> > > > available
> > > > PBN - causing any atomic state which would enable said connector to
> > > > fail
> > > > with -ENOSPC. So, let's simply workaround this by telling userspace
> > > > new
> > > > MST connectors are disconnected until we've finished probing their
> > > > PBN.
> > > > Since we always send a hotplug event at the end of the link address
> > > > probing process, userspace will still know to reprobe the connector
> > > > when
> > > > we're ready.
> > > >
> > > > Signed-off-by: Lyude Paul
> > > > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to
> > > > MST
> > > > atomic check")
> > > > Cc: Mikita Lipski
> > > > Cc: Alex Deucher
> > > > Cc: Sean Paul
> > > > Cc: Hans de Goede
> > > > ---
> > > > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > > > 1 file changed, 13 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > index 207eef08d12c..7b0ff0cff954 100644
> > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > > > *connector,
> > > > ret = connector_status_connected;
> > > > break;
> > > > }
> > > > +
> > > > + /* We don't want to tell userspace the port is actually
> > > > plugged into
> > > > +* anything until we've finished probing it's available_pbn,
> > > > otherwise
> > >
> > > "its"
> > >
> > > Why is the connector even registered before we've finished the probe?
> > >
> > Oops, I'm not sure how I did this by accident but the explanation I gave
> > in
> > the commit message was uh, completely wrong. I must have forgotten that I
> > made
> > sure we didn't expose connectors before probing their PBN back when I
> > started
> > my MST cleanup
> >
> > So: despite what I said before it's not actually when new connectors are
> > created, it's when downstream hotplugs happen which means that the
> > conenctor's
> > always going to be there before we probe the available_pbn.
>
> Not sure I understand. You're saying this is going to change for already
> existing connectors when something else gets plugged in, and either we
> zero it out during the probe or it always was zero to begin with for
> whatever reason?
ok-me and Sean Paul did some playing around with available_pbn and full_pbn
(I'll get into this one in a moment), and I also played around with a couple
of different hubs and have a much better understanding of how this should work
now.
So: first off tl;dr available_pbn is absolutely not what we want in basically
any scenario, we actually want to use the full_pbn field that we get when
sending ENUM_PATH_RESOURCES. Second, full_pbn represents the _smallest_
bandwidth limitation encountered in the path between the root MSTB and each
connected sink. Remember that there's technically a DisplayPort link trained
between each branch device going down the topology, so that bandwidth
limitation basically equates to "what is the lowest trained link rate that
exists down the path to this port?". This also means that full_pbn will
potentially change every time a new connector is plugged in, as some hubs will
be clever and optimize the link rate they decide to use. Likewise, since
there's not going to be anything trained on a disconnected port (e.g. ddps=0)
there's no point in keeping full_pbn around for disconnected ports, since
otherwise we might let userspace see a connected port with a stale full_pbn
value.
So-IMHO the behavior of not letting connectors show as connected until we also
have their full_pbn probed should definitely be the right solution here.
Especially if we want to eventually start pruning modes based on full_pbn at
some point in the future.
>
> > I did just notice
> > though that we send a hotplug on connection status notifications even
> > before
> > we've finished the PBN probe, so I might be able to improve on that as
> > well.
> > We still definitely want to report the connector as disconnected before
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Thu, 2020-03-05 at 13:52 -0500, Lyude Paul wrote:
> On Thu, 2020-03-05 at 20:29 +0200, Ville Syrjälä wrote:
> > On Thu, Mar 05, 2020 at 01:13:36PM -0500, Lyude Paul wrote:
> > > On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> > > > On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > > > > It's next to impossible for us to do connector probing on topologies
> > > > > without occasionally racing with userspace, since creating a
> > > > > connector
> > > > > itself causes a hotplug event which we have to send before probing
> > > > > the
> > > > > available PBN of a connector. Even if we didn't have this hotplug
> > > > > event
> > > > > sent, there's still always a chance that userspace started probing
> > > > > connectors before we finished probing the topology.
> > > > >
> > > > > This can be a problem when validating a new MST state since the
> > > > > connector will be shown as connected briefly, but without any
> > > > > available
> > > > > PBN - causing any atomic state which would enable said connector to
> > > > > fail
> > > > > with -ENOSPC. So, let's simply workaround this by telling userspace
> > > > > new
> > > > > MST connectors are disconnected until we've finished probing their
> > > > > PBN.
> > > > > Since we always send a hotplug event at the end of the link address
> > > > > probing process, userspace will still know to reprobe the connector
> > > > > when
> > > > > we're ready.
> > > > >
> > > > > Signed-off-by: Lyude Paul
> > > > > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to
> > > > > MST
> > > > > atomic check")
> > > > > Cc: Mikita Lipski
> > > > > Cc: Alex Deucher
> > > > > Cc: Sean Paul
> > > > > Cc: Hans de Goede
> > > > > ---
> > > > > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > > > > 1 file changed, 13 insertions(+)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > index 207eef08d12c..7b0ff0cff954 100644
> > > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > > > > *connector,
> > > > > ret = connector_status_connected;
> > > > > break;
> > > > > }
> > > > > +
> > > > > + /* We don't want to tell userspace the port is actually
> > > > > plugged into
> > > > > + * anything until we've finished probing it's available_pbn,
> > > > > otherwise
> > > >
> > > > "its"
> > > >
> > > > Why is the connector even registered before we've finished the probe?
> > > >
> > > Oops, I'm not sure how I did this by accident but the explanation I gave
> > > in
> > > the commit message was uh, completely wrong. I must have forgotten that
> > > I
> > > made
> > > sure we didn't expose connectors before probing their PBN back when I
> > > started
> > > my MST cleanup
> > >
> > > So: despite what I said before it's not actually when new connectors are
> > > created, it's when downstream hotplugs happen which means that the
> > > conenctor's
> > > always going to be there before we probe the available_pbn.
> >
> > Not sure I understand. You're saying this is going to change for already
> > existing connectors when something else gets plugged in, and either we
> > zero it out during the probe or it always was zero to begin with for
> > whatever reason?
>
> So: you just made me realize that I'm not actually sure whether there's any
> point to us clearing port->available_pbn here since the available_pbn (at
> least the value that we cache on initial link address probing for bandwidth
> constraint checking) shouldn't actually change on a port just because of a
> hotplug. I bet this is probably causing more problems on it's own as well,
> since reprobing the available_pbn might actually give us a value that
> reflects
> allocations on other ports that are already in place.
>
> So: I think what I'm going to do instead is make it so that we never clear
> port->available_pbn; mainly to make things less complicated during
> suspend/resume, since we want to make sure there's always some sort of PBN
> value populated even during the middle of reprobing the link address on
> resume. That way we don't have to pretend that it's ever disconnected
> either.
> Will send a respin in a bit.
Wait, nope, I believe I am the fool here - _supposedly_ available bw is
supposed to reflect the smallest link rate that occurs in a patch to a branch
device. I think, me and sean paul are looking at this a bit more closely. I
think I might need to do some more playing around with my hubs to make sure
this value is actually what we think it is because unfortunately the spec is
pretty vague on this from what I can tell :(
>
> > > I did just notice
> > > though that we send a hotplug on connection status notifications even
> > > before
> > > we've finished the PBN probe, so I might be able to
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Thu, 2020-03-05 at 20:29 +0200, Ville Syrjälä wrote:
> On Thu, Mar 05, 2020 at 01:13:36PM -0500, Lyude Paul wrote:
> > On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> > > On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > > > It's next to impossible for us to do connector probing on topologies
> > > > without occasionally racing with userspace, since creating a connector
> > > > itself causes a hotplug event which we have to send before probing the
> > > > available PBN of a connector. Even if we didn't have this hotplug
> > > > event
> > > > sent, there's still always a chance that userspace started probing
> > > > connectors before we finished probing the topology.
> > > >
> > > > This can be a problem when validating a new MST state since the
> > > > connector will be shown as connected briefly, but without any
> > > > available
> > > > PBN - causing any atomic state which would enable said connector to
> > > > fail
> > > > with -ENOSPC. So, let's simply workaround this by telling userspace
> > > > new
> > > > MST connectors are disconnected until we've finished probing their
> > > > PBN.
> > > > Since we always send a hotplug event at the end of the link address
> > > > probing process, userspace will still know to reprobe the connector
> > > > when
> > > > we're ready.
> > > >
> > > > Signed-off-by: Lyude Paul
> > > > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to
> > > > MST
> > > > atomic check")
> > > > Cc: Mikita Lipski
> > > > Cc: Alex Deucher
> > > > Cc: Sean Paul
> > > > Cc: Hans de Goede
> > > > ---
> > > > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > > > 1 file changed, 13 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > index 207eef08d12c..7b0ff0cff954 100644
> > > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > > > *connector,
> > > > ret = connector_status_connected;
> > > > break;
> > > > }
> > > > +
> > > > + /* We don't want to tell userspace the port is actually
> > > > plugged into
> > > > +* anything until we've finished probing it's available_pbn,
> > > > otherwise
> > >
> > > "its"
> > >
> > > Why is the connector even registered before we've finished the probe?
> > >
> > Oops, I'm not sure how I did this by accident but the explanation I gave
> > in
> > the commit message was uh, completely wrong. I must have forgotten that I
> > made
> > sure we didn't expose connectors before probing their PBN back when I
> > started
> > my MST cleanup
> >
> > So: despite what I said before it's not actually when new connectors are
> > created, it's when downstream hotplugs happen which means that the
> > conenctor's
> > always going to be there before we probe the available_pbn.
>
> Not sure I understand. You're saying this is going to change for already
> existing connectors when something else gets plugged in, and either we
> zero it out during the probe or it always was zero to begin with for
> whatever reason?
So: you just made me realize that I'm not actually sure whether there's any
point to us clearing port->available_pbn here since the available_pbn (at
least the value that we cache on initial link address probing for bandwidth
constraint checking) shouldn't actually change on a port just because of a
hotplug. I bet this is probably causing more problems on it's own as well,
since reprobing the available_pbn might actually give us a value that reflects
allocations on other ports that are already in place.
So: I think what I'm going to do instead is make it so that we never clear
port->available_pbn; mainly to make things less complicated during
suspend/resume, since we want to make sure there's always some sort of PBN
value populated even during the middle of reprobing the link address on
resume. That way we don't have to pretend that it's ever disconnected either.
Will send a respin in a bit.
>
> > I did just notice
> > though that we send a hotplug on connection status notifications even
> > before
> > we've finished the PBN probe, so I might be able to improve on that as
> > well.
> > We still definitely want to report the connector as disconnected before we
> > have the available PBN though, in case another probe was already going
> > before
> > we got the connection status notification.
> >
> > I'll make sure to fixup the explanation in the commit message on the next
> > respin
> >
> > > > +* userspace will see racy atomic check failures
> > > > +*
> > > > +* Since we always send a hotplug at the end of probing
> > > > topology
> > > > +* state, we can just let userspace reprobe this connector
> > > > later.
> > > > +*/
> > > > + if (ret == connector_status_connected && !port
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Thu, Mar 05, 2020 at 01:13:36PM -0500, Lyude Paul wrote:
> On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> > On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > > It's next to impossible for us to do connector probing on topologies
> > > without occasionally racing with userspace, since creating a connector
> > > itself causes a hotplug event which we have to send before probing the
> > > available PBN of a connector. Even if we didn't have this hotplug event
> > > sent, there's still always a chance that userspace started probing
> > > connectors before we finished probing the topology.
> > >
> > > This can be a problem when validating a new MST state since the
> > > connector will be shown as connected briefly, but without any available
> > > PBN - causing any atomic state which would enable said connector to fail
> > > with -ENOSPC. So, let's simply workaround this by telling userspace new
> > > MST connectors are disconnected until we've finished probing their PBN.
> > > Since we always send a hotplug event at the end of the link address
> > > probing process, userspace will still know to reprobe the connector when
> > > we're ready.
> > >
> > > Signed-off-by: Lyude Paul
> > > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST
> > > atomic check")
> > > Cc: Mikita Lipski
> > > Cc: Alex Deucher
> > > Cc: Sean Paul
> > > Cc: Hans de Goede
> > > ---
> > > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > > 1 file changed, 13 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index 207eef08d12c..7b0ff0cff954 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > > *connector,
> > > ret = connector_status_connected;
> > > break;
> > > }
> > > +
> > > + /* We don't want to tell userspace the port is actually plugged into
> > > + * anything until we've finished probing it's available_pbn, otherwise
> >
> > "its"
> >
> > Why is the connector even registered before we've finished the probe?
> >
> Oops, I'm not sure how I did this by accident but the explanation I gave in
> the commit message was uh, completely wrong. I must have forgotten that I made
> sure we didn't expose connectors before probing their PBN back when I started
> my MST cleanup
>
> So: despite what I said before it's not actually when new connectors are
> created, it's when downstream hotplugs happen which means that the conenctor's
> always going to be there before we probe the available_pbn.
Not sure I understand. You're saying this is going to change for already
existing connectors when something else gets plugged in, and either we
zero it out during the probe or it always was zero to begin with for
whatever reason?
> I did just notice
> though that we send a hotplug on connection status notifications even before
> we've finished the PBN probe, so I might be able to improve on that as well.
> We still definitely want to report the connector as disconnected before we
> have the available PBN though, in case another probe was already going before
> we got the connection status notification.
>
> I'll make sure to fixup the explanation in the commit message on the next
> respin
>
> > > + * userspace will see racy atomic check failures
> > > + *
> > > + * Since we always send a hotplug at the end of probing topology
> > > + * state, we can just let userspace reprobe this connector later.
> > > + */
> > > + if (ret == connector_status_connected && !port->available_pbn) {
> > > + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] not ready yet (PBN not
> > > probed)\n",
> > > + connector->base.id, connector->name);
> > > + ret = connector_status_disconnected;
> > > + }
> > > out:
> > > drm_dp_mst_topology_put_port(port);
> > > return ret;
> > > --
> > > 2.24.1
> > >
> > > ___
> > > dri-devel mailing list
> > > dri-de...@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> --
> Cheers,
> Lyude Paul (she/her)
> Associate Software Engineer at Red Hat
--
Ville Syrjälä
Intel
___
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Thu, 2020-03-05 at 15:11 +0200, Ville Syrjälä wrote:
> On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> > It's next to impossible for us to do connector probing on topologies
> > without occasionally racing with userspace, since creating a connector
> > itself causes a hotplug event which we have to send before probing the
> > available PBN of a connector. Even if we didn't have this hotplug event
> > sent, there's still always a chance that userspace started probing
> > connectors before we finished probing the topology.
> >
> > This can be a problem when validating a new MST state since the
> > connector will be shown as connected briefly, but without any available
> > PBN - causing any atomic state which would enable said connector to fail
> > with -ENOSPC. So, let's simply workaround this by telling userspace new
> > MST connectors are disconnected until we've finished probing their PBN.
> > Since we always send a hotplug event at the end of the link address
> > probing process, userspace will still know to reprobe the connector when
> > we're ready.
> >
> > Signed-off-by: Lyude Paul
> > Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST
> > atomic check")
> > Cc: Mikita Lipski
> > Cc: Alex Deucher
> > Cc: Sean Paul
> > Cc: Hans de Goede
> > ---
> > drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index 207eef08d12c..7b0ff0cff954 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector
> > *connector,
> > ret = connector_status_connected;
> > break;
> > }
> > +
> > + /* We don't want to tell userspace the port is actually plugged into
> > +* anything until we've finished probing it's available_pbn, otherwise
>
> "its"
>
> Why is the connector even registered before we've finished the probe?
>
Oops, I'm not sure how I did this by accident but the explanation I gave in
the commit message was uh, completely wrong. I must have forgotten that I made
sure we didn't expose connectors before probing their PBN back when I started
my MST cleanup
So: despite what I said before it's not actually when new connectors are
created, it's when downstream hotplugs happen which means that the conenctor's
always going to be there before we probe the available_pbn. I did just notice
though that we send a hotplug on connection status notifications even before
we've finished the PBN probe, so I might be able to improve on that as well.
We still definitely want to report the connector as disconnected before we
have the available PBN though, in case another probe was already going before
we got the connection status notification.
I'll make sure to fixup the explanation in the commit message on the next
respin
> > +* userspace will see racy atomic check failures
> > +*
> > +* Since we always send a hotplug at the end of probing topology
> > +* state, we can just let userspace reprobe this connector later.
> > +*/
> > + if (ret == connector_status_connected && !port->available_pbn) {
> > + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] not ready yet (PBN not
> > probed)\n",
> > + connector->base.id, connector->name);
> > + ret = connector_status_disconnected;
> > + }
> > out:
> > drm_dp_mst_topology_put_port(port);
> > return ret;
> > --
> > 2.24.1
> >
> > ___
> > dri-devel mailing list
> > dri-de...@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Cheers,
Lyude Paul (she/her)
Associate Software Engineer at Red Hat
___
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
Re: [PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
> It's next to impossible for us to do connector probing on topologies
> without occasionally racing with userspace, since creating a connector
> itself causes a hotplug event which we have to send before probing the
> available PBN of a connector. Even if we didn't have this hotplug event
> sent, there's still always a chance that userspace started probing
> connectors before we finished probing the topology.
>
> This can be a problem when validating a new MST state since the
> connector will be shown as connected briefly, but without any available
> PBN - causing any atomic state which would enable said connector to fail
> with -ENOSPC. So, let's simply workaround this by telling userspace new
> MST connectors are disconnected until we've finished probing their PBN.
> Since we always send a hotplug event at the end of the link address
> probing process, userspace will still know to reprobe the connector when
> we're ready.
>
> Signed-off-by: Lyude Paul
> Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST
> atomic check")
> Cc: Mikita Lipski
> Cc: Alex Deucher
> Cc: Sean Paul
> Cc: Hans de Goede
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 207eef08d12c..7b0ff0cff954 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
> ret = connector_status_connected;
> break;
> }
> +
> + /* We don't want to tell userspace the port is actually plugged into
> + * anything until we've finished probing it's available_pbn, otherwise
"its"
Why is the connector even registered before we've finished the probe?
> + * userspace will see racy atomic check failures
> + *
> + * Since we always send a hotplug at the end of probing topology
> + * state, we can just let userspace reprobe this connector later.
> + */
> + if (ret == connector_status_connected && !port->available_pbn) {
> + DRM_DEBUG_KMS("[CONNECTOR:%d:%s] not ready yet (PBN not
> probed)\n",
> + connector->base.id, connector->name);
> + ret = connector_status_disconnected;
> + }
> out:
> drm_dp_mst_topology_put_port(port);
> return ret;
> --
> 2.24.1
>
> ___
> dri-devel mailing list
> dri-de...@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Ville Syrjälä
Intel
___
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
[PATCH 2/3] drm/dp_mst: Don't show connectors as connected before probing available PBN
It's next to impossible for us to do connector probing on topologies
without occasionally racing with userspace, since creating a connector
itself causes a hotplug event which we have to send before probing the
available PBN of a connector. Even if we didn't have this hotplug event
sent, there's still always a chance that userspace started probing
connectors before we finished probing the topology.
This can be a problem when validating a new MST state since the
connector will be shown as connected briefly, but without any available
PBN - causing any atomic state which would enable said connector to fail
with -ENOSPC. So, let's simply workaround this by telling userspace new
MST connectors are disconnected until we've finished probing their PBN.
Since we always send a hotplug event at the end of the link address
probing process, userspace will still know to reprobe the connector when
we're ready.
Signed-off-by: Lyude Paul
Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic
check")
Cc: Mikita Lipski
Cc: Alex Deucher
Cc: Sean Paul
Cc: Hans de Goede
---
drivers/gpu/drm/drm_dp_mst_topology.c | 13 +
1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 207eef08d12c..7b0ff0cff954 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
ret = connector_status_connected;
break;
}
+
+ /* We don't want to tell userspace the port is actually plugged into
+* anything until we've finished probing it's available_pbn, otherwise
+* userspace will see racy atomic check failures
+*
+* Since we always send a hotplug at the end of probing topology
+* state, we can just let userspace reprobe this connector later.
+*/
+ if (ret == connector_status_connected && !port->available_pbn) {
+ DRM_DEBUG_KMS("[CONNECTOR:%d:%s] not ready yet (PBN not
probed)\n",
+ connector->base.id, connector->name);
+ ret = connector_status_disconnected;
+ }
out:
drm_dp_mst_topology_put_port(port);
return ret;
--
2.24.1
___
amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
