[PATCH v2 3/3] drm/i915/dp_mst: Work around out-of-spec adapters filtering short pulses

[Imre Deak]

Some TypeC -> native DP adapters, at least the Club CAC-1557 adapter,
incorrectly filter out HPD short pulses with a duration less than ~540
usec, leading to MST probe failures.

According to the DP alt mode specification adapters should forward short
pulses with a duration greater than 250 usec. According to the DP
specificatin DP sources should detect short pulses in the
500 usec -> 2 ms range. Based on this filtering out short pulses with a
duration less than 540 usec is incorrect.

To make such adapters work add support for a driver polling on MST
inerrupt flags, and wire this up in the i915 driver. The sink can clear
an interrupt it raised after 110 ms if the source doesn't respond, so
use a 50 ms poll period to avoid missing an interrupt. Polling of the
MST interrupt flags is explicitly allowed by the DP specification.

This fixes MST probe failures I saw using this adapter and a DELL U2515H
monitor.

v2:
- Fix the wait event timeout for the no-poll case.

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c       | 19 ++++++++++++++++---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 15 +++++++++++++++
 include/drm/drm_dp_mst_helper.h             |  1 +
 3 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 5bc72e800b85..4e987a513df8 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1178,11 +1178,24 @@ static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
 				    struct drm_dp_sideband_msg_tx *txmsg)
 {
 	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
+	unsigned long wait_timeout = msecs_to_jiffies(4000);
+	unsigned long wait_expires = jiffies + wait_timeout;
 	int ret;
 
-	ret = wait_event_timeout(mgr->tx_waitq,
-				 check_txmsg_state(mgr, txmsg),
-				 (4 * HZ));
+	for (;;) {
+		ret = wait_event_timeout(mgr->tx_waitq,
+					 check_txmsg_state(mgr, txmsg),
+					 mgr->cbs->update_hpd_irq_state ?
+						msecs_to_jiffies(50) :
+						wait_timeout);
+
+		if (ret || !mgr->cbs->update_hpd_irq_state ||
+		    time_after(jiffies, wait_expires))
+			break;
+
+		mgr->cbs->update_hpd_irq_state(mgr);
+	}
+
 	mutex_lock(&mgr->qlock);
 	if (ret > 0) {
 		if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index d18b406f2a7d..1ff7d0096262 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -765,8 +765,23 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 	return NULL;
 }
 
+static void
+intel_dp_mst_update_hpd_irq_state(struct drm_dp_mst_topology_mgr *mgr)
+{
+	struct intel_dp *intel_dp = container_of(mgr, struct intel_dp, mst_mgr);
+	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
+	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
+
+	spin_lock_irq(&i915->irq_lock);
+	i915->hotplug.short_port_mask |= BIT(dig_port->base.port);
+	spin_unlock_irq(&i915->irq_lock);
+
+	queue_work(i915->hotplug.dp_wq, &i915->hotplug.dig_port_work);
+}
+
 static const struct drm_dp_mst_topology_cbs mst_cbs = {
 	.add_connector = intel_dp_add_mst_connector,
+	.update_hpd_irq_state = intel_dp_mst_update_hpd_irq_state,
 };
 
 static struct intel_dp_mst_encoder *
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 9e1ffcd7cb68..c902f4380200 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -475,6 +475,7 @@ struct drm_dp_mst_topology_mgr;
 struct drm_dp_mst_topology_cbs {
 	/* create a connector for a port */
 	struct drm_connector *(*add_connector)(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_mst_port *port, const char *path);
+	void (*update_hpd_irq_state)(struct drm_dp_mst_topology_mgr *mgr);
 };
 
 #define DP_MAX_PAYLOAD (sizeof(unsigned long) * 8)
-- 
2.23.1