[Intel-gfx] [PATCH] drm/i915: Wait one vblank before sending hotplug event to userspace

[Mika Kahola]

Occasionally, we get the following error in our CI runs

[853.132830] Workqueue: events i915_hotplug_work_func [i915]
[853.132844] RIP: 0010:drm_wait_one_vblank+0x19b/0x1b0
[853.132852] Code: fe ff ff e8 b7 4e a6 ff 48 89 e6 4c 89 ff e8 6c 5f ab ff 45 85 ed 0f 85
15 ff ff ff 89 ee 48 c7 c7 e8 03 10 82 e8 b5 4b a6 ff <0f> 0b e9 00 ff ff ff 0f 1f 40 00 66
2e 0f 1f 84 00 00 00 00 00 8b
[853.132859] RSP: 0018:ffffc9000146bca0 EFLAGS: 00010286
[853.132866] RAX: 0000000000000000 RBX: ffff88849ef00000 RCX: 0000000000000000
[853.132873] RDX: 0000000000000007 RSI: ffffffff820c6f58 RDI: 00000000ffffffff
[853.132879] RBP: 0000000000000000 R08: 000000007ffc637a R09: 0000000000000000
[853.132884] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[853.132890] R13: 0000000000000000 R14: 000000000000d0c2 R15: ffff8884a491e680
[853.132897] FS:  0000000000000000(0000) GS:ffff8884afe80000(0000) knlGS:0000000000000000
[853.132904] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[853.132910] CR2: 00007f63bf0df000 CR3: 0000000005210006 CR4: 0000000000760ee0
[853.132916] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[853.132922] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[853.132927] PKRU: 55555554
[853.132932] Call Trace:
[853.132949]  ? wait_woken+0xa0/0xa0
[853.133068]  intel_dp_retrain_link+0x130/0x190 [i915]
[853.133176]  intel_ddi_hotplug+0x54/0x2e0 [i915]
[853.133298]  i915_hotplug_work_func+0x1a9/0x240 [i915]
[853.133324]  process_one_work+0x262/0x630
[853.133349]  worker_thread+0x37/0x380
[853.133365]  ? process_one_work+0x630/0x630
[853.133373]  kthread+0x119/0x130
[853.133383]  ? kthread_park+0x80/0x80
[853.133400]  ret_from_fork+0x3a/0x50
[853.133433] irq event stamp: 1426928

I suspect that this is caused by a racy condition when retraining the
DisplayPort link. My proposal is to wait for one additional vblank
event before we send out a hotplug event to userspace for reprobing.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108835

Cc: Manasi Navare <manasi.d.navare at intel.com>
Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index a6907a1761ab..6ce7d54e49af 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -6746,6 +6746,10 @@ static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
 {
 	struct intel_connector *intel_connector;
 	struct drm_connector *connector;
+	struct drm_connector_state *conn_state;
+	struct drm_i915_private *dev_priv;
+	struct intel_crtc *crtc;
+	struct intel_crtc_state *crtc_state;
 
 	intel_connector = container_of(work, typeof(*intel_connector),
 				       modeset_retry_work);
@@ -6753,6 +6757,14 @@ static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n", connector->base.id,
 		      connector->name);
 
+	dev_priv = to_i915(connector->dev);
+	conn_state = intel_connector->base.state;
+
+	crtc = to_intel_crtc(conn_state->crtc);
+	crtc_state = to_intel_crtc_state(crtc->base.state);
+
+	WARN_ON(!intel_crtc_has_dp_encoder(crtc_state));
+
 	/* Grab the locks before changing connector property*/
 	mutex_lock(&connector->dev->mode_config.mutex);
 	/* Set connector link status to BAD and send a Uevent to notify
@@ -6761,6 +6773,21 @@ static void intel_dp_modeset_retry_work_fn(struct work_struct *work)
 	drm_connector_set_link_status_property(connector,
 					       DRM_MODE_LINK_STATUS_BAD);
 	mutex_unlock(&connector->dev->mode_config.mutex);
+
+	/* Suppress underruns caused by re-training */
+	intel_set_cpu_fifo_underrun_reporting(dev_priv, crtc->pipe, false);
+	if (crtc_state->has_pch_encoder)
+		intel_set_pch_fifo_underrun_reporting(dev_priv,
+						      intel_crtc_pch_transcoder(crtc), false);
+
+	/* Keep underrun reporting disabled until things are stable */
+	intel_wait_for_vblank(dev_priv, crtc->pipe);
+
+	intel_set_cpu_fifo_underrun_reporting(dev_priv, crtc->pipe, true);
+	if (crtc_state->has_pch_encoder)
+		intel_set_pch_fifo_underrun_reporting(dev_priv,
+						      intel_crtc_pch_transcoder(crtc), true);
+
 	/* Send Hotplug uevent so userspace can reprobe */
 	drm_kms_helper_hotplug_event(connector->dev);
 }
-- 
2.17.1