Re: [PATCH v2 16/27] drm/dp_mst: Refactor pdt setup/teardown, add more locking

Sean Paul
2019-09-27T13:30:16Z

On Wed, Sep 25, 2019 at 05:00:00PM -0400, Lyude Paul wrote:
> On Wed, 2019-09-25 at 15:27 -0400, Sean Paul wrote:
> > On Tue, Sep 03, 2019 at 04:45:54PM -0400, Lyude Paul wrote:
> > > Since we're going to be implementing suspend/resume reprobing very soon,
> > > we need to make sure we are extra careful to ensure that our locking
> > > actually protects the topology state where we expect it to. Turns out
> > > this isn't the case with drm_dp_port_setup_pdt() and
> > > drm_dp_port_teardown_pdt(), both of which change port->mstb without
> > > grabbing &mgr->lock.
> > >
> > > Additionally, since most callers of these functions are just using it to
> > > teardown the port's previous PDT and setup a new one we can simplify
> > > things a bit and combine drm_dp_port_setup_pdt() and
> > > drm_dp_port_teardown_pdt() into a single function:
> > > drm_dp_port_set_pdt(). This function also handles actually ensuring that
> > > we grab the correct locks when we need to modify port->mstb.
> > >
> > > 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>
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > > ---
> > > drivers/gpu/drm/drm_dp_mst_topology.c | 181 +++++++++++++++-----------
> > > include/drm/drm_dp_mst_helper.h | 6 +-
> > > 2 files changed, 110 insertions(+), 77 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > index d1610434a0cb..9944ef2ce885 100644
> > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> > > @@ -1487,24 +1487,6 @@ drm_dp_mst_topology_put_mstb(struct
> > > drm_dp_mst_branch *mstb)
> > > kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
> > > }
> > >
> > > -static void drm_dp_port_teardown_pdt(struct drm_dp_mst_port *port, int
> > > old_pdt)
> > > -{
> > > - struct drm_dp_mst_branch *mstb;
> > > -
> > > - switch (old_pdt) {
> > > - case DP_PEER_DEVICE_DP_LEGACY_CONV:
> > > - case DP_PEER_DEVICE_SST_SINK:
> > > - /* remove i2c over sideband */
> > > - drm_dp_mst_unregister_i2c_bus(&port->aux);
> > > - break;
> > > - case DP_PEER_DEVICE_MST_BRANCHING:
> > > - mstb = port->mstb;
> > > - port->mstb = NULL;
> > > - drm_dp_mst_topology_put_mstb(mstb);
> > > - break;
> > > - }
> > > -}
> > > -
> > > static void drm_dp_destroy_port(struct kref *kref)
> > > {
> > > struct drm_dp_mst_port *port =
> > > @@ -1714,38 +1696,79 @@ static u8 drm_dp_calculate_rad(struct
> > > drm_dp_mst_port *port,
> > > return parent_lct + 1;
> > > }
> > >
> > > -/*
> > > - * return sends link address for new mstb
> > > - */
> > > -static bool drm_dp_port_setup_pdt(struct drm_dp_mst_port *port)
> > > +static int drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt)
> > > {
> > > - int ret;
> > > - u8 rad[6], lct;
> > > - bool send_link = false;
> > > + struct drm_dp_mst_topology_mgr *mgr = port->mgr;
> > > + struct drm_dp_mst_branch *mstb;
> > > + u8 rad[8], lct;
> > > + int ret = 0;
> > > +
> > > + if (port->pdt == new_pdt)
> >
> > Shouldn't we also ensure that access to port->pdt is also locked?
> >
>
> It's specifically port->mstb that needs to be protected under lock. We don't
> use port->pdt for traversing the topology at all, so keeping it under
> connection_mutex is sufficient.
>

I hadn't gotten to the connection_mutex patch yet when I made that comment :)

Reviewed-by: Sean Paul <sean@poorly.run>

> > Sean
> >
> > > + return 0;
> > > +
> > > + /* Teardown the old pdt, if there is one */
> > > + switch (port->pdt) {
> > > + case DP_PEER_DEVICE_DP_LEGACY_CONV:
> > > + case DP_PEER_DEVICE_SST_SINK:
> > > + /*
> > > + * If the new PDT would also have an i2c bus, don't bother
> > > + * with reregistering it
> > > + */
> > > + if (new_pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
> > > + new_pdt == DP_PEER_DEVICE_SST_SINK) {
> > > + port->pdt = new_pdt;
> > > + return 0;
> > > + }
> > > +
> > > + /* remove i2c over sideband */
> > > + drm_dp_mst_unregister_i2c_bus(&port->aux);
> > > + break;
> > > + case DP_PEER_DEVICE_MST_BRANCHING:
> > > + mutex_lock(&mgr->lock);
> > > + drm_dp_mst_topology_put_mstb(port->mstb);
> > > + port->mstb = NULL;
> > > + mutex_unlock(&mgr->lock);
> > > + break;
> > > + }
> > > +
> > > + port->pdt = new_pdt;
> > > switch (port->pdt) {
> > > case DP_PEER_DEVICE_DP_LEGACY_CONV:
> > > case DP_PEER_DEVICE_SST_SINK:
> > > /* add i2c over sideband */
> > > ret = drm_dp_mst_register_i2c_bus(&port->aux);
> > > break;
> > > +
> > > case DP_PEER_DEVICE_MST_BRANCHING:
> > > lct = drm_dp_calculate_rad(port, rad);
> > > + mstb = drm_dp_add_mst_branch_device(lct, rad);
> > > + if (!mstb) {
> > > + ret = -ENOMEM;
> > > + DRM_ERROR("Failed to create MSTB for port %p", port);
> > > + goto out;
> > > + }
> > >
> > > - port->mstb = drm_dp_add_mst_branch_device(lct, rad);
> > > - if (port->mstb) {
> > > - port->mstb->mgr = port->mgr;
> > > - port->mstb->port_parent = port;
> > > - /*
> > > - * Make sure this port's memory allocation stays
> > > - * around until its child MSTB releases it
> > > - */
> > > - drm_dp_mst_get_port_malloc(port);
> > > + mutex_lock(&mgr->lock);
> > > + port->mstb = mstb;
> > > + mstb->mgr = port->mgr;
> > > + mstb->port_parent = port;
> > >
> > > - send_link = true;
> > > - }
> > > + /*
> > > + * Make sure this port's memory allocation stays
> > > + * around until its child MSTB releases it
> > > + */
> > > + drm_dp_mst_get_port_malloc(port);
> > > + mutex_unlock(&mgr->lock);
> > > +
> > > + /* And make sure we send a link address for this */
> > > + ret = 1;
> > > break;
> > > }
> > > - return send_link;
> > > +
> > > +out:
> > > + if (ret < 0)
> > > + port->pdt = DP_PEER_DEVICE_NONE;
> > > + return ret;
> > > }
> > >
> > > /**
> > > @@ -1881,10 +1904,9 @@ static void drm_dp_add_port(struct
> > > drm_dp_mst_branch *mstb,
> > > struct drm_device *dev,
> > > struct drm_dp_link_addr_reply_port *port_msg)
> > > {
> > > + struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> > > struct drm_dp_mst_port *port;
> > > - bool ret;
> > > bool created = false;
> > > - int old_pdt = 0;
> > > int old_ddps = 0;
> > >
> > > port = drm_dp_get_port(mstb, port_msg->port_number);
> > > @@ -1896,7 +1918,7 @@ static void drm_dp_add_port(struct drm_dp_mst_branch
> > > *mstb,
> > > kref_init(&port->malloc_kref);
> > > port->parent = mstb;
> > > port->port_num = port_msg->port_number;
> > > - port->mgr = mstb->mgr;
> > > + port->mgr = mgr;
> > > port->aux.name = "DPMST";
> > > port->aux.dev = dev->dev;
> > > port->aux.is_remote = true;
> > > @@ -1909,11 +1931,9 @@ static void drm_dp_add_port(struct
> > > drm_dp_mst_branch *mstb,
> > >
> > > created = true;
> > > } else {
> > > - old_pdt = port->pdt;
> > > old_ddps = port->ddps;
> > > }
> > >
> > > - port->pdt = port_msg->peer_device_type;
> > > port->input = port_msg->input_port;
> > > port->mcs = port_msg->mcs;
> > > port->ddps = port_msg->ddps;
> > > @@ -1925,29 +1945,33 @@ static void drm_dp_add_port(struct
> > > drm_dp_mst_branch *mstb,
> > > /* manage mstb port lists with mgr lock - take a reference
> > > for this list */
> > > if (created) {
> > > - mutex_lock(&mstb->mgr->lock);
> > > + mutex_lock(&mgr->lock);
> > > drm_dp_mst_topology_get_port(port);
> > > list_add(&port->next, &mstb->ports);
> > > - mutex_unlock(&mstb->mgr->lock);
> > > + mutex_unlock(&mgr->lock);
> > > }
> > >
> > > if (old_ddps != port->ddps) {
> > > if (port->ddps) {
> > > if (!port->input) {
> > > - drm_dp_send_enum_path_resources(mstb->mgr,
> > > - mstb, port);
> > > + drm_dp_send_enum_path_resources(mgr, mstb,
> > > + port);
> > > }
> > > } else {
> > > port->available_pbn = 0;
> > > }
> > > }
> > >
> > > - if (old_pdt != port->pdt && !port->input) {
> > > - drm_dp_port_teardown_pdt(port, old_pdt);
> > > -
> > > - ret = drm_dp_port_setup_pdt(port);
> > > - if (ret == true)
> > > - drm_dp_send_link_address(mstb->mgr, port->mstb);
> > > + if (!port->input) {
> > > + int ret = drm_dp_port_set_pdt(port,
> > > + port_msg->peer_device_type);
> > > + if (ret == 1) {
> > > + drm_dp_send_link_address(mgr, port->mstb);
> > > + } else if (ret < 0) {
> > > + DRM_ERROR("Failed to change PDT on port %p: %d\n",
> > > + port, ret);
> > > + goto fail;
> > > + }
> > > }
> > >
> > > if (created && !port->input) {
> > > @@ -1955,18 +1979,11 @@ static void drm_dp_add_port(struct
> > > drm_dp_mst_branch *mstb,
> > >
> > > build_mst_prop_path(mstb, port->port_num, proppath,
> > > sizeof(proppath));
> > > - port->connector = (*mstb->mgr->cbs->add_connector)(mstb->mgr,
> > > - port,
> > > - proppath);
> > > - if (!port->connector) {
> > > - /* remove it from the port list */
> > > - mutex_lock(&mstb->mgr->lock);
> > > - list_del(&port->next);
> > > - mutex_unlock(&mstb->mgr->lock);
> > > - /* drop port list reference */
> > > - drm_dp_mst_topology_put_port(port);
> > > - goto out;
> > > - }
> > > + port->connector = (*mgr->cbs->add_connector)(mgr, port,
> > > + proppath);
> > > + if (!port->connector)
> > > + goto fail;
> > > +
> > > if ((port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV ||
> > > port->pdt == DP_PEER_DEVICE_SST_SINK) &&
> > > port->port_num >= DP_MST_LOGICAL_PORT_0) {
> > > @@ -1974,28 +1991,38 @@ static void drm_dp_add_port(struct
> > > drm_dp_mst_branch *mstb,
> > > &port->aux.ddc);
> > > drm_connector_set_tile_property(port->connector);
> > > }
> > > - (*mstb->mgr->cbs->register_connector)(port->connector);
> > > +
> > > + (*mgr->cbs->register_connector)(port->connector);
> > > }
> > >
> > > -out:
> > > /* put reference to this port */
> > > drm_dp_mst_topology_put_port(port);
> > > + return;
> > > +
> > > +fail:
> > > + /* Remove it from the port list */
> > > + mutex_lock(&mgr->lock);
> > > + list_del(&port->next);
> > > + mutex_unlock(&mgr->lock);
> > > +
> > > + /* Drop the port list reference */
> > > + drm_dp_mst_topology_put_port(port);
> > > + /* And now drop our reference */
> > > + drm_dp_mst_topology_put_port(port);
> > > }
> > >
> > > static void drm_dp_update_port(struct drm_dp_mst_branch *mstb,
> > > struct drm_dp_connection_status_notify
> > > *conn_stat)
> > > {
> > > struct drm_dp_mst_port *port;
> > > - int old_pdt;
> > > int old_ddps;
> > > bool dowork = false;
> > > +
> > > port = drm_dp_get_port(mstb, conn_stat->port_number);
> > > if (!port)
> > > return;
> > >
> > > old_ddps = port->ddps;
> > > - old_pdt = port->pdt;
> > > - port->pdt = conn_stat->peer_device_type;
> > > port->mcs = conn_stat->message_capability_status;
> > > port->ldps = conn_stat->legacy_device_plug_status;
> > > port->ddps = conn_stat->displayport_device_plug_status;
> > > @@ -2007,11 +2034,17 @@ static void drm_dp_update_port(struct
> > > drm_dp_mst_branch *mstb,
> > > port->available_pbn = 0;
> > > }
> > > }
> > > - if (old_pdt != port->pdt && !port->input) {
> > > - drm_dp_port_teardown_pdt(port, old_pdt);
> > >
> > > - if (drm_dp_port_setup_pdt(port))
> > > + if (!port->input) {
> > > + int ret = drm_dp_port_set_pdt(port,
> > > + conn_stat->peer_device_type);
> > > + if (ret == 1) {
> > > dowork = true;
> > > + } else if (ret < 0) {
> > > + DRM_ERROR("Failed to change PDT for port %p: %d\n",
> > > + port, ret);
> > > + dowork = false;
> > > + }
> > > }
> > >
> > > drm_dp_mst_topology_put_port(port);
> > > @@ -4003,9 +4036,7 @@ drm_dp_delayed_destroy_port(struct drm_dp_mst_port
> > > *port)
> > > if (port->connector)
> > > port->mgr->cbs->destroy_connector(port->mgr, port->connector);
> > >
> > > - drm_dp_port_teardown_pdt(port, port->pdt);
> > > - port->pdt = DP_PEER_DEVICE_NONE;
> > > -
> > > + drm_dp_port_set_pdt(port, DP_PEER_DEVICE_NONE);
> > > drm_dp_mst_put_port_malloc(port);
> > > }
> > >
> > > diff --git a/include/drm/drm_dp_mst_helper.h
> > > b/include/drm/drm_dp_mst_helper.h
> > > index 5423a8adda78..f253ee43e9d9 100644
> > > --- a/include/drm/drm_dp_mst_helper.h
> > > +++ b/include/drm/drm_dp_mst_helper.h
> > > @@ -55,8 +55,10 @@ struct drm_dp_vcpi {
> > > * @num_sdp_stream_sinks: Number of stream sinks
> > > * @available_pbn: Available bandwidth for this port.
> > > * @next: link to next port on this branch device
> > > - * @mstb: branch device attach below this port
> > > - * @aux: i2c aux transport to talk to device connected to this port.
> > > + * @mstb: branch device on this port, protected by
> > > + * &drm_dp_mst_topology_mgr.lock
> > > + * @aux: i2c aux transport to talk to device connected to this port,
> > > protected
> > > + * by &drm_dp_mst_topology_mgr.lock
> > > * @parent: branch device parent of this port
> > > * @vcpi: Virtual Channel Payload info for this port.
> > > * @connector: DRM connector this port is connected to.
> > > --
> > > 2.21.0
> > >
> --
> Cheers,
> Lyude Paul
>

--
Sean Paul, Software Engineer, Google / Chromium OS