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

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On 4/8/2024 1:41 PM, Bjorn Andersson wrote:
On Mon, Apr 08, 2024 at 12:43:34PM -0700, Abhinav Kumar wrote:


On 4/7/2024 11:48 AM, Bjorn Andersson wrote:
On Fri, Apr 05, 2024 at 08:15:47PM -0700, Abhinav Kumar wrote:
From: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
[..]
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);

If I read the code correctly, and we get an external connect event
inbetween a previous disconnect and the related disable call, this
should result in a PLUG_INT being injected into the queue still.

Will that not cause the same problem?

Regards,
Bjorn


Yes, your observation is correct and I had asked the same question to kuogee
before taking over this change and posting.

We will have to handle that case separately. I don't have a good solution
yet for it without requiring further rework or we drop the below snippet.

         if (state == ST_DISCONNECT_PENDING) {
                 /* wait until ST_DISCONNECTED */
                 dp_add_event(dp, EV_HPD_PLUG_INT, 0, 1); /* delay = 1 */
                 mutex_unlock(&dp->event_mutex);
                 return 0;
         }

I will need sometime to address that use-case as I need to see if we can
handle that better and then drop the the DISCONNECT_PENDING state to address
this fully. But it needs more testing.

But, we will need this patch anyway because without this we will not be able
to fix even the most regular and commonly seen case of basic
connect/disconnect receiving complementary events.


I did some more testing on this patch. Connecting and disconnecting the
cable while in fbcon works reliably, except for:

Thanks for the tests !

- edid/modes are not read before we bring up the link so I always end up
   with 640x480


hmmm, I wonder why this should be affected due to this patch. We always read the EDID during hpd_connect() and the selected resolution will be programmed with the modeset. We will retry this with our x1e80100 and see.

- if I run modetest -s <id>:<mode> the link is brought up with the new
   resolution and I get my test image on the screen.
   But as we're shutting down the link for the resolution chance I end up
   in dp_bridge_hpd_notify() with link_ready && state = disconnected.
   This triggers an unplug which hangs on the event_mutex, such that as
   soon as I get the test image, the state machine enters
   DISCONNECT_PENDING. This is immediately followed by another
   !link_ready && status = connected, which attempts to perform the plug
   operation, but as we're in DISCONNECT_PENDING this is posted on the
   event queue. From there I get a log entry from my PLUG_INT, every
   100ms stating that we're still in DISCONNECT_PENDING. If I exit
   modetest the screen goes black, and no new mode can be selected,
   because we're in DISCONNECT_PENDING. The only way out is to disconnect
   the cable to complete the DISCONNECT_PENDING.


I am going to run this test-case and see what we can do.

Regards,
Bjorn


   	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




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