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

[Louis Li]

[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 500ms 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 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..043ddac73862 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 they drive HPD signal high.
+     */
+    mdelay(500);
+
 	/* 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