First time to enable radeon.dpm=1 Screen ends up dark (dead??) neither different kernel versions, nor Windows are able to recover it. Replaced the LCD once just to be sure it was the kernel which killed it. The new screen died after a couple of hours. Booted Windows first, it worked, rebooted in Linux - worked fine, but died after rebooting. HDMI output still works. Laptop is Lenovo U165 (AMD K325 CPU, RS880M [Mobility Radeon HD 4200 Series] GPU)
Please attach your xorg log and dmesg output.
Created attachment 117351 [details] Xorg.log
Created attachment 117361 [details] dmesg
It looks like maybe you have a loose or bad connection to the LCD panel. As you can see in your log, the driver isn't even detecting a panel: [drm] Radeon Display Connectors [drm] Connector 0: [drm] VGA-1 [drm] DDC: 0x7e40 0x7e40 0x7e44 0x7e44 0x7e48 0x7e48 0x7e4c 0x7e4c [drm] Encoders: [drm] CRT1: INTERNAL_KLDSCP_DAC1 [drm] Connector 1: [drm] HDMI-A-1 [drm] HPD1 [drm] DDC: 0x7e60 0x7e60 0x7e64 0x7e64 0x7e68 0x7e68 0x7e6c 0x7e6c [drm] Encoders: [drm] DFP1: INTERNAL_UNIPHY
Yes, that is the problem, the screen is dead! If I attach a brand new LCD panel it works... but I don't really want to buy a second one now. There isn't any obvious damage on the panel, but today I swapped it with the original one and they both doesn't work. Kernel reports disconnection, but it's a damage or malfunction.
Can you test the panel on another system? Sound to me like a hw problem. Maybe a wonky connector on the motherboard? Does jiggling or pressing on the connector help?
I connected a third panel today and it works, the two old ones do not! It's not the connector, just the panels were somehow rendered unusable. I don't really know how to investigate further as the panel is a complete unit, which is hard to open. There is no backlight and there is not even the faintest of image on the LCD. Another strange thing is that, when booting with radeon.dpm=1, even the HDMI output doesn't work after doing the mode setting and before KDE is started. Without this parameter I can see all kernel messages at boot time.