[PATCH v2] drm/amd/display: Fix Apple dongle cannot be successfully detected

[Li, Ching-shih (Louis)]

Hi reviewers,

What is the review result for this patch? Customer is pushing on this change to merge. TKS for your attention.

BR,
Louis

-----Original Message-----
From: Louis Li <Ching-shih.Li at amd.com> 
Sent: Thursday, November 14, 2019 11:42 AM
To: amd-gfx at lists.freedesktop.org
Cc: Kazlauskas, Nicholas <Nicholas.Kazlauskas at amd.com>; Wentland, Harry <Harry.Wentland at amd.com>; Li, Ching-shih (Louis) <Ching-shih.Li at amd.com>
Subject: [PATCH v2] drm/amd/display: Fix Apple dongle cannot be successfully detected

[Why]
External monitor cannot be displayed consistently, if connecting via this Apple dongle (A1621, USB Type-C to HDMI).
By experiments, it is confirmed that the dongle needs 200ms at least to be ready for communication, after it sets HPD signal high.

[How]
When receiving HPD IRQ, delay 300ms at the beginning of handle_hpd_irq().
Then run the original procedure.
With this patch applied, the problem cannot be reproduced.
With other dongles, test results are PASS.
Test result is PASS to plug in HDMI cable while playing video, and the video is being playing smoothly.
Test result is PASS after system resumes from suspend.

Signed-off-by: Louis Li <Ching-shih.Li at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 0aef92b7c037..5b844b6a5a59 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -1025,6 +1025,11 @@ static void handle_hpd_irq(void *param)
 	struct drm_device *dev = connector->dev;
 	enum dc_connection_type new_connection_type = dc_connection_none;
 
+	/* Some monitors/dongles need around 200ms to be ready for communication
+	 * after those devices drive HPD signal high.
+	 */
+	msleep(300);
+
 	/* In case of failure or MST no need to update connector status or notify the OS
 	 * since (for MST case) MST does this in it's own context.
 	 */
--
2.21.0