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SubjectRe: [PATCH 06/26] drm/dp_mst: Move PDT teardown for ports into destroy_connector_work
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On Tue, 2019-08-13 at 16:52 +0200, Daniel Vetter wrote:
> On Wed, Jul 17, 2019 at 09:42:29PM -0400, Lyude Paul wrote:
> > This will allow us to add some locking for port PDTs, which can't be
> > done from drm_dp_destroy_port() since we don't know what locks the
> > caller might be holding. Also, this gets rid of a good bit of unneeded
> > code.
> >
> > Cc: Juston Li <juston.li@intel.com>
> > Cc: Imre Deak <imre.deak@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Harry Wentland <hwentlan@amd.com>
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > ---
> > drivers/gpu/drm/drm_dp_mst_topology.c | 42 +++++++++++----------------
> > 1 file changed, 17 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > index defc5e09fb9a..0295e007c836 100644
> > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > @@ -1509,31 +1509,22 @@ static void drm_dp_destroy_port(struct kref *kref)
> > container_of(kref, struct drm_dp_mst_port, topology_kref);
> > struct drm_dp_mst_topology_mgr *mgr = port->mgr;
> >
> > - if (!port->input) {
> > - kfree(port->cached_edid);
> > -
> > - /*
> > - * The only time we don't have a connector
> > - * on an output port is if the connector init
> > - * fails.
> > - */
> > - if (port->connector) {
> > - /* we can't destroy the connector here, as
> > - * we might be holding the mode_config.mutex
> > - * from an EDID retrieval */
> > -
> > - mutex_lock(&mgr->destroy_connector_lock);
> > - list_add(&port->next, &mgr->destroy_connector_list);
> > - mutex_unlock(&mgr->destroy_connector_lock);
> > - schedule_work(&mgr->destroy_connector_work);
> > - return;
> > - }
> > - /* no need to clean up vcpi
> > - * as if we have no connector we never setup a vcpi */
> > - drm_dp_port_teardown_pdt(port, port->pdt);
> > - port->pdt = DP_PEER_DEVICE_NONE;
> > + /* There's nothing that needs locking to destroy an input port yet */
> > + if (port->input) {
> > + drm_dp_mst_put_port_malloc(port);
> > + return;
> > }
> > - drm_dp_mst_put_port_malloc(port);
> > +
> > + kfree(port->cached_edid);
> > +
> > + /*
> > + * we can't destroy the connector here, as we might be holding the
> > + * mode_config.mutex from an EDID retrieval
> > + */
> > + mutex_lock(&mgr->destroy_connector_lock);
> > + list_add(&port->next, &mgr->destroy_connector_list);
> > + mutex_unlock(&mgr->destroy_connector_lock);
> > + schedule_work(&mgr->destroy_connector_work);
>
> So if I'm not completely blind this just flattens the above code flow (by
> inverting the if (port->input)).

Now I'm really remembering why I refactored this. The control flow on the
previous version of this is pretty misleading. To summarize so it's a bit more
obvious:

if (port->input) {
drm_dp_mst_put_port_malloc(port);
return;
} else if (port->connector) {
add_connector_to_destroy_list();
return;
/* ^ now, this is where PDT teardown happens */
} else {
drm_dp_port_teardown_pdt(port, port->pdt);
}
/* free edid etc etc */

So, I suppose the title of this patch would be more accurate if it was
"drm/dp_mst: Remove PDT teardown in destroy_port() and refactor"
I'll go ahead and change that

>
> > }
> >
> > /**
> > @@ -3881,7 +3872,8 @@ drm_dp_finish_destroy_port(struct drm_dp_mst_port
> > *port)
> > {
> > INIT_LIST_HEAD(&port->next);
> >
> > - port->mgr->cbs->destroy_connector(port->mgr, port->connector);
> > + if (port->connector)
>
> And this here I can't connect with the commit message. I'm confused, did
> something go wrong with some rebase here, and this patch should have a
> different title/summary?
> -Daniel

No, this is correct. In the previous drm_dp_destroy_port() function we only
added a port to the delayed destroy work if it had a connector on it. Now that
we add ports unconditionally, we have to check port->connector before trying
to call port->mgr->cbs->destroy_connector() since port->connector is no longer
guaranteed to be != NULL.

>
> > + port->mgr->cbs->destroy_connector(port->mgr, port->connector);
> >
> > drm_dp_port_teardown_pdt(port, port->pdt);
> > port->pdt = DP_PEER_DEVICE_NONE;
> > --
> > 2.21.0
> >
--
Cheers,
Lyude Paul

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