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

Sean Paul
2019-09-25T19:27:54Z

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?

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
>

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