linux-kernel - Re: [PATCH v3] drm/msm/dp: call dp_hpd_plug_handle()/unplug

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Message-ID: <b7ed299d-4cf7-8829-fd7f-e518aef05fb2@quicinc.com>
Date: Mon, 8 Apr 2024 14:08:47 -0700
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
CC: <freedreno@...ts.freedesktop.org>, Rob Clark <robdclark@...il.com>,
        "Dmitry Baryshkov" <dmitry.baryshkov@...aro.org>,
        Sean Paul
	<sean@...rly.run>,
        "Marijn Suijten" <marijn.suijten@...ainline.org>,
        David
 Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Kuogee Hsieh
	<quic_khsieh@...cinc.com>,
        <dri-devel@...ts.freedesktop.org>, <seanpaul@...omium.org>,
        <swboyd@...omium.org>, <quic_jesszhan@...cinc.com>,
        <quic_bjorande@...cinc.com>, <johan@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] drm/msm/dp: call dp_hpd_plug_handle()/unplug_handle()
 directly for external HPD



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@...cinc.com>
>>> [..]
>>>> 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
>>>>