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From: Wentland, Harry Harry.Wentland@amd.com Sent: Thursday, June 17, 2021 03:53 To: Lin, Wayne; dri-devel@lists.freedesktop.org Cc: lyude@redhat.com; Kazlauskas, Nicholas; Zuo, Jerry; Pillai, Aurabindo; Maarten Lankhorst; Maxime Ripard; Thomas Zimmermann; stable@vger.kernel.org Subject: Re: [PATCH v2 1/2] drm/dp_mst: Do not set proposed vcpi directly

On 2021-06-15 11:55 p.m., Wayne Lin wrote:

...

[Why] When we receive CSN message to notify one port is disconnected, we will implicitly set its corresponding num_slots to 0. Later on, we will eventually call drm_dp_update_payload_part1() to arrange down streams.

In drm_dp_update_payload_part1(), we iterate over all proposed_vcpis[] to do the update. Not specific to a target sink only. For example, if we light up 2 monitors, Monitor_A and Monitor_B, and then we unplug Monitor_B. Later on, when we call drm_dp_update_payload_part1() to try to update payload for Monitor_A, we'll also implicitly clean payload for Monitor_B at the same time. And finally, when we try to call drm_dp_update_payload_part1() to clean payload for Monitor_B, we will do nothing at this time since payload for Monitor_B has been cleaned up previously.

For StarTech 1to3 DP hub, it seems like if we didn't update DPCD payload ID table then polling for "ACT Handled"(BIT_1 of DPCD 002C0h) will fail and this polling will last for 3 seconds.

Therefore, guess the best way is we don't set the proposed_vcpi[] diretly. Let user of these herlper functions to set the proposed_vcpi directly.

[How]

1. Revert commit 7617e9621bf2 ("drm/dp_mst: clear time slots for ports

invalid") 2. Tackle the issue in previous commit by skipping those trasient proposed VCPIs. These stale VCPIs shoulde be explicitly cleared by user later on.

Changes since v1:

• Change debug macro to use drm_dbg_kms() instead
• Amend the commit message to add Fixed & Cc tags

Signed-off-by: Wayne Lin Wayne.Lin@amd.com Fixes: 7617e9621bf2 ("drm/dp_mst: clear time slots for ports invalid") Cc: Lyude Paul lyude@redhat.com Cc: Wayne Lin Wayne.Lin@amd.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v5.5+

---

drivers/gpu/drm/drm_dp_mst_topology.c | 36 ++++++++------------------- 1 file changed, 10 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 32b7f8983b94..b41b837db66d 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -2501,7 +2501,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb, { struct drm_dp_mst_topology_mgr *mgr = mstb->mgr; struct drm_dp_mst_port *port;

• int old_ddps, old_input, ret, i;
  

• int old_ddps, ret;
  u8 new_pdt;
  bool new_mcs;
  bool dowork = false, create_connector = false;
  

@@ -2533,7 +2533,6 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb, }

  old_ddps = port->ddps;

• old_input = port->input;
  port->input = conn_stat->input_port;
  port->ldps = conn_stat->legacy_device_plug_status;
  port->ddps = conn_stat->displayport_device_plug_status;
  

@@ -2555,28 +2554,6 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb, dowork = false; }

• if (!old_input && old_ddps != port->ddps && !port->ddps) {
  

•         for (i = 0; i < mgr->max_payloads; i++) {
  

•                 struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
  

•                 struct drm_dp_mst_port *port_validated;
  

•                 if (!vcpi)
  

•                         continue;
  

•                 port_validated =
  

•                         container_of(vcpi, struct drm_dp_mst_port, vcpi);
  

•                 port_validated =
  

•                         drm_dp_mst_topology_get_port_validated(mgr, port_validated);
  

•                 if (!port_validated) {
  

•                         mutex_lock(&mgr->payload_lock);
  

•                         vcpi->num_slots = 0;
  

•                         mutex_unlock(&mgr->payload_lock);
  

•                 } else {
  

•                         drm_dp_mst_topology_put_port(port_validated);
  

•                 }
  

•         }
  

• }
  

• if (port->connector)
          drm_modeset_unlock(&mgr->base.lock);
  else if (create_connector)
  

@@ -3410,8 +3387,15 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr) port = drm_dp_mst_topology_get_port_validated( mgr, port); if (!port) {

•                                 mutex_unlock(&mgr->payload_lock);
  

•                                 return -EINVAL;
  

•                                 if (vcpi->num_slots == payload->num_slots) {
  

•                                         cur_slots += vcpi->num_slots;
  

•                                         payload->start_slot = req_payload.start_slot;
  

•                                         continue;
  

•                                 } else {
  

•                                         drm_dbg_kms("Fail:set payload to invalid sink");
  

drm_dbg_kms takes a drm_device as first parameter.

Harry

Thanks Harry. Should be addressed by another patch provided by José.

...

•                                         mutex_unlock(&mgr->payload_lock);
  

•                                         return -EINVAL;
  

•                                 }
                          }
                          put_port = true;
                  }
  
  

-- Regards, Wayne

On Wed, 2021-06-16 at 11:55 +0800, Wayne Lin wrote:

[Why] After unplug/hotplug hub from the system, userspace might start to clear stale payloads gradually. If we call drm_dp_mst_deallocate_vcpi() to release stale VCPI of those ports which are not relating to current topology, we have chane to wrongly clear active payload table entry for current topology.

E.g. We have allocated VCPI 1 in current payload table and we call drm_dp_mst_deallocate_vcpi() to clean VCPI 1 in stale topology. In drm_dp_mst_deallocate_vcpi(), it will call drm_dp_mst_put_payload_id() tp put VCPI 1 and which means ID 1 is available again. Thereafter, if we want to allocate a new payload stream, it will find ID 1 is available by drm_dp_mst_assign_payload_id(). However, ID 1 is being used

[How] Check target sink is relating to current topology or not before doing any payload table update. Searching upward to find the target sink's relevant root branch device. If the found root branch device is not the same root of current topology, don't update payload table.

Changes since v1:

• Change debug macro to use drm_dbg_kms() instead
• Amend the commit message to add Cc tag.

Signed-off-by: Wayne Lin Wayne.Lin@amd.com Cc: stable@vger.kernel.org

---

drivers/gpu/drm/drm_dp_mst_topology.c | 29 +++++++++++++++++++++++++++ 1 file changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index b41b837db66d..9ac148efd9e4 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -94,6 +94,9 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port); static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port); static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);

+static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,

• 				 struct drm_dp_mst_branch *branch);
  

#define DBG_PREFIX "[dp_mst]"

#define DP_STR(x) [DP_ ## x] = #x @@ -3366,6 +3369,7 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr) struct drm_dp_mst_port *port; int i, j; int cur_slots = 1;

• bool skip;

  mutex_lock(&mgr->payload_lock); for (i = 0; i < mgr->max_payloads; i++) {

@@ -3380,6 +3384,14 @@ int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr) port = container_of(vcpi, struct drm_dp_mst_port, vcpi);

• 	mutex_lock(&mgr->lock);
  

• 	skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
  

• 	mutex_unlock(&mgr->lock);
  

• 	if (skip) {
  

• 		drm_dbg_kms("Virtual channel %d is not in current topology\n", i);
  

Missing dev/drm parameter and breaking the build.

• 		continue;
  

• 	}
  /* Validated ports don't matter if we're releasing
   * VCPI
   */
  

@@ -3479,6 +3491,7 @@ int drm_dp_update_payload_part2(struct drm_dp_mst_topology_mgr *mgr) struct drm_dp_mst_port *port; int i; int ret = 0;

• bool skip;

  mutex_lock(&mgr->payload_lock); for (i = 0; i < mgr->max_payloads; i++) {

@@ -3488,6 +3501,13 @@ int drm_dp_update_payload_part2(struct drm_dp_mst_topology_mgr *mgr)

port = container_of(mgr->proposed_vcpis[i], struct drm_dp_mst_port, vcpi);

• mutex_lock(&mgr->lock);
  

• skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
  

• mutex_unlock(&mgr->lock);
  

• if (skip)
  

• 	continue;
  

• drm_dbg_kms(mgr->dev, "payload %d %d\n", i, mgr->payloads[i].payload_state); if (mgr->payloads[i].payload_state == DP_PAYLOAD_LOCAL) { ret = drm_dp_create_payload_step2(mgr, port, mgr->proposed_vcpis[i]->vcpi, &mgr->payloads[i]);

@@ -4574,9 +4594,18 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots); void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port) {

• bool skip;

• if (!port->vcpi.vcpi) return;

• mutex_lock(&mgr->lock);

• skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);

• mutex_unlock(&mgr->lock);

• if (skip)

• return;
  

• drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi); port->vcpi.num_slots = 0; port->vcpi.pbn = 0;