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

[Johan Hovold <johan@kernel.org>]

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.

I see these pairs of identical notification when connecting the stock
charger to one of the ports directly, and I noticed that they repeat
every 90 seconds here. After plugging and unplugging a bunch of devices
I think they stopped at one point, but they were there again after a
reboot.

So there's something going on with the PMIC GLINK firmware or driver on
the X13s. I did not see these repeated messages on the T14s with just a
charger (and I don't have a dock to test with).

> > UDEV  [236.150574] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [236.588696] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [266.208175] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [266.644710] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [296.243187] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [296.678177] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [326.276256] change   /devices/platform/soc@0/ae00000.display-subsystem/ae01000.display-controller/drm/card0 (drm)
> > UDEV  [326.712248] change   /devices/platform/soc@0/ae00000.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!

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?

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

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

Thanks for testing.

Johan