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

Lyude Paul
2019-09-25T21:00:12Z

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.

> 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