[PATCH v3] drm/msm/dp: call dp_hpd_plug_handle()/unplug_handle() directly for external HPD

[Abhinav Kumar]

From: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>

For HPD events coming from external modules using drm_bridge_hpd_notify(),
the sequence of calls leading to dp_bridge_hpd_notify() is like below:

dp_bridge_hpd_notify+0x18/0x70 [msm]
drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
drm_helper_probe_detect+0x94/0xc0 [drm_kms_helper]
drm_helper_probe_single_connector_modes+0x43c/0x53c [drm_kms_helper]
drm_client_modeset_probe+0x240/0x1114 [drm]
drm_fb_helper_hotplug_event.part.26+0x9c/0xe8 [drm_kms_helper]
drm_fb_helper_hotplug_event+0x24/0x38 [drm_kms_helper]
msm_fbdev_client_hotplug+0x24/0xd4 [msm]
drm_client_dev_hotplug+0xd8/0x148 [drm]
drm_kms_helper_connector_hotplug_event+0x30/0x3c [drm_kms_helper]
drm_bridge_connector_handle_hpd+0x84/0x94 [drm_kms_helper]
drm_bridge_connector_hpd_cb+0xc/0x14 [drm_kms_helper]
drm_bridge_hpd_notify+0x38/0x50 [drm]
drm_aux_hpd_bridge_notify+0x14/0x20 [aux_hpd_bridge]
pmic_glink_altmode_worker+0xec/0x27c [pmic_glink_altmode]
process_scheduled_works+0x17c/0x2cc
worker_thread+0x2ac/0x2d0
kthread+0xfc/0x120

There are three notifications delivered to DP driver for each notification event.

1) From the drm_aux_hpd_bridge_notify() itself as shown above

2) From output_poll_execute() thread which arises due to
drm_helper_probe_single_connector_modes() call of the above stacktrace
as shown in more detail here.

dp_bridge_hpd_notify+0x18/0x70 [msm]
drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
drm_helper_probe_detect+0x94/0xc0 [drm_kms_helper]
drm_helper_probe_single_connector_modes+0x43c/0x53c [drm_kms_helper]
drm_client_modeset_probe+0x240/0x1114 [drm]
drm_fb_helper_hotplug_event.part.26+0x9c/0xe8 [drm_kms_helper]
drm_fb_helper_hotplug_event+0x24/0x38 [drm_kms_helper]
msm_fbdev_client_hotplug+0x24/0xd4 [msm]
drm_client_dev_hotplug+0xd8/0x148 [drm]
drm_kms_helper_hotplug_event+0x30/0x3c [drm_kms_helper]
output_poll_execute+0xe0/0x210 [drm_kms_helper]

3) From the DP driver as the dp_bridge_hpd_notify() callback today triggers
the hpd_event_thread for connect and disconnect events respectively via below stack

dp_bridge_hpd_notify+0x18/0x70 [msm]
drm_bridge_connector_detect+0x60/0xe8 [drm_kms_helper]
drm_helper_probe_detect_ctx+0x98/0x110 [drm_kms_helper]
check_connector_changed+0x4c/0x20c [drm_kms_helper]
drm_helper_hpd_irq_event+0x98/0x120 [drm_kms_helper]
hpd_event_thread+0x478/0x5bc [msm]

dp_bridge_hpd_notify() delivered from output_poll_execute() thread
returns the incorrect HPD status as the MSM DP driver returns the value
of link_ready and not the HPD status currently in the .detect() callback.

And because the HPD event thread has not run yet, this results in two complementary
events.

To address this, fix dp_bridge_hpd_notify() to call dp_hpd_plug_handle/unplug_handle()
directly to return consistent values for the above scenarios.

changes in v3:
	- Fix the commit message as per submitting guidelines.
	- remove extra line added

changes in v2:
	- Fix the commit message to explain the scenario
	- Fix the subject a little as well

Fixes: 542b37efc20e ("drm/msm/dp: Implement hpd_notify()")
Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index d80f89581760..bfb6dfff27e8 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -1665,7 +1665,7 @@ void dp_bridge_hpd_notify(struct drm_bridge *bridge,
 		return;
 
 	if (!dp_display->link_ready && status == connector_status_connected)
-		dp_add_event(dp, EV_HPD_PLUG_INT, 0, 0);
+		dp_hpd_plug_handle(dp, 0);
 	else if (dp_display->link_ready && status == connector_status_disconnected)
-		dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
+		dp_hpd_unplug_handle(dp, 0);
 }
-- 
2.43.2