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

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Message-ID: <dd1bc01c-75f4-4071-a2ac-534a12dd3029@craftyguy.net>
Date: Mon, 24 Mar 2025 10:05:44 -0700
From: Clayton Craft <clayton@...ftyguy.net>
To: Johan Hovold <johan+linaro@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>
Cc: 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 3/24/25 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:
> 
>      KERNEL[1556.223776] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
>      ACTION=change
>      DEVPATH=/devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0
>      SUBSYSTEM=drm
>      HOTPLUG=1
>      CONNECTOR=36
>      DEVNAME=/dev/dri/card0
>      DEVTYPE=drm_minor
>      SEQNUM=4176
>      MAJOR=226
>      MINOR=0
> 
> On the Lenovo ThinkPad X13s and T14s, the PMIC GLINK firmware sends two
> identical notifications with orientation information when connecting a
> charger, each generating a bogus DRM hotplug event. On the X13s, two
> such notification are also sent every 90 seconds while a charger remains
> connected, which again are forwarded to user space:
> 
>      port = 1, svid = ff00, mode = 255, hpd_state = 0
>      payload = 01 00 00 00 00 00 00 ff 00 00 00 00 00 00 00 00
> 
> Note that the firmware only sends on of these when connecting an
> ethernet adapter.
> 
> Fix the spurious hotplug events by only forwarding hotplug notifications
> for the Type-C DisplayPort service id. This also reduces the number of
> uevents from four to two when an actual DisplayPort altmode device is
> connected:
> 
>      port = 0, svid = ff01, mode = 2, hpd_state = 0
>      payload = 00 01 02 00 f2 0c 01 ff 03 00 00 00 00 00 00 00
>      port = 0, svid = ff01, mode = 2, hpd_state = 1
>      payload = 00 01 02 00 f2 0c 01 ff 43 00 00 00 00 00 00 00
> 
> Fixes: 080b4e24852b ("soc: qcom: pmic_glink: Introduce altmode support")
> Cc: stable@...r.kernel.org	# 6.3
> Cc: Bjorn Andersson <andersson@...nel.org>
> Reported-by: Clayton Craft <clayton@...ftyguy.net>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
> 
> 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?

> UDEV  [236.150574] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [236.588696] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [266.208175] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [266.644710] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [296.243187] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [296.678177] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [326.276256] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> UDEV  [326.712248] change   /devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)

Not sure about you seeing it every 90s vs my 30s... anyways, I no longer 
see these events when a PD charger is connected though, so this patch 
seems to help with that!

Tested-by: Clayton Craft <clayton@...ftyguy.net>