linux-kernel - Re: [PATCH] soc: qcom: pmic_glink_altmode: fix spurious DP hotplug events

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Message-ID: <7e287401-98c4-413f-8108-134d5e43d279@craftyguy.net>
Date: Tue, 1 Apr 2025 11:18:49 -0700
From: Clayton Craft <clayton@...ftyguy.net>
To: Johan Hovold <johan@...nel.org>
Cc: Johan Hovold <johan+linaro@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: pmic_glink_altmode: fix spurious DP hotplug
 events

On 3/26/25 07:43, Johan Hovold wrote:
> On Tue, Mar 25, 2025 at 09:32:10AM +0100, Johan Hovold wrote:
>> On Mon, Mar 24, 2025 at 10:05:44AM -0700, Clayton Craft wrote:
>>> On 3/24/25 06:24, Johan Hovold wrote:
>>>> The PMIC GLINK driver is currently generating DisplayPort hotplug
>>>> notifications whenever something is connected to (or disconnected from)
>>>> a port regardless of the type of notification sent by the firmware.
>>>>
>>>> These notifications are forwarded to user space by the DRM subsystem as
>>>> connector "change" uevents:
>>
>>>> ---
>>>>
>>>> Clayton reported seeing display flickering with recent RC kernels, which
>>>> may possibly be related to these spurious events being generated with
>>>> even greater frequency.
>>>>
>>>> That still remains to be fully understood, but the spurious events, that
>>>> on the X13s are generated every 90 seconds, should be fixed either way.
>>>
>>> When a display/dock (which has ethernet) is connected, I see this
>>> hotplug change event 2 times (every 30 seconds) which I think you said
>>> this is expected now?
>>
>> I didn't realise you were also using a display/dock. Bjorn mentioned
>> that he has noticed issues with one of his monitors (e.g. built-in hub
>> reenumerating repeatedly iirc) which may be related.

Sorry for the confusion, let me clarify:

The original issue I reported to you on IRC was *without* a 
dock/external display attached, only a PD adapter was attached. With 
your patch, I no longer see these drm hotplug events in this scenario.

After confirming that your patch resolved the spurious hotplug events 
when using a PD charger, I connected a dock+external display to see if 
the patch caused any regressions there for me. It was here that I 
noticed a periodic hotplug event firing 2 times every 30 seconds was 
still showing up. I don't know if this is expected or not, I've never 
noticed it before because I wasn't monitoring udev events.

>> Just so I understand you correctly here, you're no longer seeing the
>> repeated uevents with this patch? Both when using a dock and when using
>> a charger directly?

With PD charger only: no more spurious hotplug events firing

With dock+external displauy: 2x hotplug events every 30s.

>>
>> Did it help with the display flickering too? Was that only on the
>> external display?

The flickering was only on the internal display, and your patch here 
seems to have resolved that.

-Clayton