HDMI: spurious Hot Plug Detect

[Vicente Bergas]

Hi!
I am using the Rockchip Sapphire board (RK3399) as a desktop computer.
Linux kernel version is 4.15.3, as found in ArchLinuxArm.
The display is connected to the HDMI port.

When idling I execute
  xset dpms force off
to save power.
During this state, the usb-disk activity LED flashes continuously.
That has been tracked down to uevents sent from the kernel:

$ udevadm monitor -kp
monitor will print the received events for:
KERNEL - the kernel uevent

KERNEL[16801.562895] change
/devices/platform/display-subsystem/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/platform/display-subsystem/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
MAJOR=226
MINOR=0
SEQNUM=4685
SUBSYSTEM=drm

KERNEL[16802.075817] change
/devices/platform/display-subsystem/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/platform/display-subsystem/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
MAJOR=226
MINOR=0
SEQNUM=4686
SUBSYSTEM=drm

KERNEL[16809.148972] change
/devices/platform/display-subsystem/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/platform/display-subsystem/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
MAJOR=226
MINOR=0
SEQNUM=4687
SUBSYSTEM=drm

KERNEL[16809.896870] change
/devices/platform/display-subsystem/drm/card0 (drm)
ACTION=change
DEVNAME=/dev/dri/card0
DEVPATH=/devices/platform/display-subsystem/drm/card0
DEVTYPE=drm_minor
HOTPLUG=1
MAJOR=226
MINOR=0
SEQNUM=4688
SUBSYSTEM=drm


The messages come in pairs: an UnPlug event shortly followed by a Plug event.
Then it repeats every 7 seconds.
I was not expecting that because the display is not being disconnected
and reconnected, never.

Is that a bug?

Regards,
  Vicente.