Thanks everybody. Maybe I'll try another cable and a different PSU, though I read it's recommended to use the original one...
I just realized.. I have one more problem that I had for ages already and it corresponds to my CEC problem:
When switching to a different HDMI source on the TV and back, the CEC remote stopped working. Only when I play a media file, the functionality comes back.
Here the cec-client log:
LibreELEC:~ # cec-client
No device type given. Using 'recording device'
CEC Parser created - libCEC version 4.0.7
no serial port given. trying autodetect:
path: /dev/cec0
com port: Linux
opening a connection to the CEC adapter...
DEBUG: [ 51] Broadcast (F): osd name set to 'Broadcast'
DEBUG: [ 51] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 51] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 51] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 51] could not open a connection (try 1)
DEBUG: [ 51] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 1051] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 1051] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 1051] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 1051] could not open a connection (try 2)
DEBUG: [ 1051] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 2052] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 2052] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 2052] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 2052] could not open a connection (try 3)
DEBUG: [ 2052] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 3052] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 3052] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 3053] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 3053] could not open a connection (try 4)
DEBUG: [ 3053] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 4054] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 4055] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 4055] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 4056] could not open a connection (try 5)
DEBUG: [ 4057] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 5058] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 5058] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 5058] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 5059] could not open a connection (try 6)
DEBUG: [ 5059] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 6060] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 6060] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 6061] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 6061] could not open a connection (try 7)
DEBUG: [ 6061] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 7062] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 7062] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 7063] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 7063] could not open a connection (try 8)
DEBUG: [ 7063] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 8064] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 8065] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 8065] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 8065] could not open a connection (try 9)
DEBUG: [ 8065] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 9066] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 9067] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 9067] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 9067] could not open a connection (try 10)
DEBUG: [ 9067] CLinuxCECAdapterCommunication::Close - m_fd=-1
NOTICE: [ 10068] connection opened
ERROR: [ 10068] could not start CEC communications
unable to open the device on port Linux
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This is the log after I started playing a media file and CEC remote worked again:
LibreELEC:~ # cec-client
No device type given. Using 'recording device'
CEC Parser created - libCEC version 4.0.7
no serial port given. trying autodetect:
path: /dev/cec0
com port: Linux
opening a connection to the CEC adapter...
DEBUG: [ 33] Broadcast (F): osd name set to 'Broadcast'
DEBUG: [ 33] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 33] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 33] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 33] could not open a connection (try 1)
DEBUG: [ 33] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 1033] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 1033] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 1033] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 1033] could not open a connection (try 2)
DEBUG: [ 1033] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 2034] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 2034] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 2034] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 2034] could not open a connection (try 3)
DEBUG: [ 2034] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 3034] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 3034] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 3034] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 3034] could not open a connection (try 4)
DEBUG: [ 3034] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 4035] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 4035] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 4035] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 4035] could not open a connection (try 5)
DEBUG: [ 4035] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 5036] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 5036] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 5036] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 5036] could not open a connection (try 6)
DEBUG: [ 5036] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 6037] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 6037] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 6037] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 6037] could not open a connection (try 7)
DEBUG: [ 6037] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 7037] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 7037] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 7037] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 7037] could not open a connection (try 8)
DEBUG: [ 7037] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 8038] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 8038] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 8038] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 8038] could not open a connection (try 9)
DEBUG: [ 8038] CLinuxCECAdapterCommunication::Close - m_fd=-1
DEBUG: [ 9038] CLinuxCECAdapterCommunication::Open - m_fd=3 bStartListening=1
ERROR: [ 9038] CLinuxCECAdapterCommunication::Open - ioctl CEC_S_MODE failed - errno=16
DEBUG: [ 9038] CLinuxCECAdapterCommunication::Close - m_fd=3
ERROR: [ 9038] could not open a connection (try 10)
DEBUG: [ 9038] CLinuxCECAdapterCommunication::Close - m_fd=-1
unable to open the device on port Linux
NOTICE: [ 10039] connection opened
Display More
Is there a setting I have to change?
/edit: SOLUTION
I added hdmi_force_hotplug=1 to /flash/config.txt and no it kinda works. Needs some time to get activated (about 5 seconds).