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

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Date: Mon, 8 Apr 2024 14:17:29 -0700
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Bjorn Andersson <andersson@...nel.org>, <freedreno@...ts.freedesktop.org>,
        Rob Clark <robdclark@...il.com>, 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 2:13 PM, Dmitry Baryshkov wrote:
> On Tue, 9 Apr 2024 at 00:08, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>
>>
>>
>> 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.
> 
> BTW, why is EDID read during HPD handling? I always supposed that it
> can be read much later, when the DRM framework calls the get_modes /
> get_edid callbacks.
> 

Well, dp_panel_read_sink_caps() is in dp_display_process_hpd_high() 
currently. We read the edid there.

get_modes(), parses the EDID and adds the modes using drm_add_edid_modes().

>>
>>> - 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
>>>>>>
> 
> 
>