[SOLVED ?] Distorted graphics on Compal FL90 with ATI HD3650

[Maxxis]

Hi,
I have old Compal FL90 which had corrupted nVidia card which has been replaced with ATI mobility Radeon HD3650.

It worked perfectly fine with new card on Windows XP but on Linux there is a problem with distorted graphics on laptop LCD. There are no problems on external monitor. Screen looks like old analogue TV with poor distorted signal. Picture is not stable and there us usually moving lines. I tried multiple different Linux distributions, and usually distortions looks similar but not the same.

I though that this card is not supported correctly on Linux with Compal FL90 since it is not original configuration, however I found one Linux distribution which works : PartedMagic
I compared configuration printouts on PartedMagic and Mint and I see that card name is somehow different and there are also differences in vertical and horizontal frequencies although remaining settings looks the same. Could it be the problem that I don;t have exactly 60Hz but 59,97 Hz ? How to change that ?
Parted Magic:

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root@PartedMagic:/media/sdb1# lspci | grep VGA
01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI RV635 [Mobility Radeon HD 3650]
root@PartedMagic:/media/sdb1# lshw -C video
  *-display               
       description: VGA compatible controller
       product: RV635 [Mobility Radeon HD 3650]
       vendor: Advanced Micro Devices [AMD] nee ATI
       physical id: 0
       bus info: pci@0000:01:00.0
       version: 00
       width: 64 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0
       resources: irq:16 memory:d0000000-dfffffff memory:c7ef0000-c7efffff ioport:2000(size=256) memory:c7e00000-c7e1ffff
root@PartedMagic:/media/sdb1# xrandr --verbose
Screen 0: minimum 320 x 200, current 1280 x 800, maximum 8192 x 8192
LVDS connected 1280x800+0+0 (0x55) normal (normal left inverted right x axis y axis) 331mm x 207mm
	Identifier: 0x51
	Timestamp:  39275
	Subpixel:   horizontal rgb
	Gamma:      1.0:1.0:1.0
	Brightness: 1.0
	Clones:    
	CRTC:       0
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	EDID:
		00ffffffffffff000e14011400000000
		26110103802115780a743d9857518f28
		21505400000001010101010101010101
		010101010101ea1a0080502010302020
		13004bcf100000190000000f00202020
		2020202020206e050f00000000fe0043
		50540a202020202020202020000000fe
		00434c4141313534574230334120004f
	scaling mode:	Full
		supported: None         Full         Center       Full aspect 
  1280x800 (0x55)   68.9MHz -HSync -VSync *current +preferred
        h: width  1280 start 1312 end 1344 total 1408 skew    0 clock   48.9KHz
        v: height  800 start  801 end  804 total  816           clock   60.0Hz
  1280x720 (0x56)   74.5MHz -HSync +VSync
        h: width  1280 start 1344 end 1472 total 1664 skew    0 clock   44.8KHz
        v: height  720 start  723 end  728 total  748           clock   59.9Hz
  1152x768 (0x57)   71.8MHz -HSync +VSync
        h: width  1152 start 1216 end 1328 total 1504 skew    0 clock   47.7KHz
        v: height  768 start  771 end  781 total  798           clock   59.8Hz
  1024x768 (0x58)   63.5MHz -HSync +VSync
        h: width  1024 start 1072 end 1176 total 1328 skew    0 clock   47.8KHz
        v: height  768 start  771 end  775 total  798           clock   59.9Hz
  800x600 (0x59)   38.2MHz -HSync +VSync
        h: width   800 start  832 end  912 total 1024 skew    0 clock   37.4KHz
        v: height  600 start  603 end  607 total  624           clock   59.9Hz
  848x480 (0x5a)   31.5MHz -HSync +VSync
        h: width   848 start  872 end  952 total 1056 skew    0 clock   29.8KHz
        v: height  480 start  483 end  493 total  500           clock   59.7Hz
  720x480 (0x5b)   26.8MHz -HSync +VSync
        h: width   720 start  744 end  808 total  896 skew    0 clock   29.9KHz
        v: height  480 start  483 end  493 total  500           clock   59.7Hz
  640x480 (0x5c)   23.8MHz -HSync +VSync
        h: width   640 start  664 end  720 total  800 skew    0 clock   29.7KHz
        v: height  480 start  483 end  487 total  500           clock   59.4Hz
VGA-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x52
	Timestamp:  39275
	Subpixel:   no subpixels
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	load detection: 1 (0x00000001)	range:  (0,1)
HDMI-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x53
	Timestamp:  39275
	Subpixel:   horizontal rgb
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	underscan vborder: 0 (0x00000000)	range:  (0,128)
	underscan hborder: 0 (0x00000000)	range:  (0,128)
	underscan:	off
		supported: off          on           auto        
	coherent: 1 (0x00000001)	range:  (0,1)
DVI-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x54
	Timestamp:  39275
	Subpixel:   horizontal rgb
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	load detection: 1 (0x00000001)	range:  (0,1)
	underscan vborder: 0 (0x00000000)	range:  (0,128)
	underscan hborder: 0 (0x00000000)	range:  (0,128)
	underscan:	off
		supported: off          on           auto        
	coherent: 1 (0x00000001)	range:  (0,1)
root@PartedMagic:/media/sdb1#  

Mint:

Code: Select all

user@compal:~/Pulpit$ lspci | grep VGA
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV635/M86 [Mobility Radeon HD 3650]
user@compal:~/Pulpit$ lshw -C video
WARNING: you should run this program as super-user.
  *-display                 
       description: VGA compatible controller
       product: RV635/M86 [Mobility Radeon HD 3650]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 0
       bus info: pci@0000:01:00.0
       version: 00
       width: 64 bits
       clock: 33MHz
       capabilities: vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0
       resources: irq:32 memory:d0000000-dfffffff memory:c7ef0000-c7efffff ioport:2000(size=256) memory:c0000-dffff
WARNING: output may be incomplete or inaccurate, you should run this program as super-user.
user@compal:~/Pulpit$ xrandr --verbose
Screen 0: minimum 320 x 200, current 1280 x 800, maximum 8192 x 8192
LVDS connected primary 1280x800+0+0 (0x56) normal (normal left inverted right x axis y axis) 331mm x 207mm
	Identifier: 0x51
	Timestamp:  35726
	Subpixel:   horizontal rgb
	Gamma:      1.0:1.0:1.0
	Brightness: 1.0
	Clones:    
	CRTC:       0
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	EDID: 
		00ffffffffffff000e14011400000000
		26110103802115780a743d9857518f28
		21505400000001010101010101010101
		010101010101ea1a0080502010302020
		13004bcf100000190000000f00202020
		2020202020206e050f00000000fe0043
		50540a202020202020202020000000fe
		00434c4141313534574230334120004f
	TearFree: auto 
		supported: off, on, auto
	scaling mode: Full 
		supported: None, Full, Center, Full aspect
	link-status: Good 
		supported: Good, Bad
	CONNECTOR_ID: 46 
		supported: 46
	non-desktop: 0 
		range: (0, 1)
  1280x800 (0x56) 68.900MHz -HSync -VSync *current +preferred
        h: width  1280 start 1312 end 1344 total 1408 skew    0 clock  48.93KHz
        v: height  800 start  801 end  804 total  816           clock  59.97Hz
  1280x720 (0x57) 74.648MHz -HSync +VSync
        h: width  1280 start 1344 end 1472 total 1664 skew    0 clock  44.86KHz
        v: height  720 start  723 end  728 total  748           clock  59.97Hz
  1152x768 (0x58) 71.951MHz -HSync +VSync
        h: width  1152 start 1216 end 1328 total 1504 skew    0 clock  47.84KHz
        v: height  768 start  771 end  781 total  798           clock  59.95Hz
  1024x768 (0x59) 63.531MHz -HSync +VSync
        h: width  1024 start 1072 end 1176 total 1328 skew    0 clock  47.84KHz
        v: height  768 start  771 end  775 total  798           clock  59.95Hz
  800x600 (0x5a) 38.313MHz -HSync +VSync
        h: width   800 start  832 end  912 total 1024 skew    0 clock  37.42KHz
        v: height  600 start  603 end  607 total  624           clock  59.96Hz
  848x480 (0x5b) 31.648MHz -HSync +VSync
        h: width   848 start  872 end  952 total 1056 skew    0 clock  29.97KHz
        v: height  480 start  483 end  493 total  500           clock  59.94Hz
  720x480 (0x5c) 26.852MHz -HSync +VSync
        h: width   720 start  744 end  808 total  896 skew    0 clock  29.97KHz
        v: height  480 start  483 end  493 total  500           clock  59.94Hz
  640x480 (0x5d) 23.975MHz -HSync +VSync
        h: width   640 start  664 end  720 total  800 skew    0 clock  29.97KHz
        v: height  480 start  483 end  487 total  500           clock  59.94Hz
VGA-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x52
	Timestamp:  35726
	Subpixel:   no subpixels
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	TearFree: auto 
		supported: off, on, auto
	scaling mode: None 
		supported: None, Full, Center, Full aspect
	load detection: 1 
		range: (0, 1)
	link-status: Good 
		supported: Good, Bad
	CONNECTOR_ID: 48 
		supported: 48
	non-desktop: 0 
		range: (0, 1)
HDMI-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x53
	Timestamp:  35726
	Subpixel:   horizontal rgb
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	TearFree: auto 
		supported: off, on, auto
	audio: auto 
		supported: off, on, auto
	scaling mode: None 
		supported: None, Full, Center, Full aspect
	dither: off 
		supported: off, on
	underscan vborder: 0 
		range: (0, 128)
	underscan hborder: 0 
		range: (0, 128)
	underscan: off 
		supported: off, on, auto
	coherent: 1 
		range: (0, 1)
	link-status: Good 
		supported: Good, Bad
	CONNECTOR_ID: 50 
		supported: 50
	non-desktop: 0 
		range: (0, 1)
DVI-0 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x54
	Timestamp:  35726
	Subpixel:   horizontal rgb
	Clones:    
	CRTCs:      0 1
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	TearFree: auto 
		supported: off, on, auto
	load detection: 1 
		range: (0, 1)
	audio: auto 
		supported: off, on, auto
	scaling mode: None 
		supported: None, Full, Center, Full aspect
	dither: off 
		supported: off, on
	underscan vborder: 0 
		range: (0, 128)
	underscan hborder: 0 
		range: (0, 128)
	underscan: off 
		supported: off, on, auto
	coherent: 1 
		range: (0, 1)
	link-status: Good 
		supported: Good, Bad
	CONNECTOR_ID: 51 
		supported: 51
	non-desktop: 0 
		range: (0, 1)
user@compal:~/Pulpit$ 

 

Inxxi PartedMagic:

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System:    Host: PartedMagic Kernel: 3.5.6-pmagic i686 bits: 32 compiler: gcc v: 4.7.1 
           Desktop: Openbox 3.5.0 Distro: Parted Magic 2012_10_10 
Machine:   Type: Laptop Mobo: - model: IFL90 v: IFT00 serial: N/A BIOS: COMPAL v: 1.18 
           date: 06/18/2008 
CPU:       Info: Dual Core model: Intel Core2 Duo T7500 bits: 64 type: MCP arch: Core Merom rev: B 
           cache: L2: 4 MiB 
           flags: lm pae sse sse2 sse3 ssse3 vmx bogomips: 8777 
           Speed: 800 MHz min/max: 800/2201 MHz Core speeds (MHz): 1: 800 2: 800 
Graphics:  Device-1: AMD ATI RV635 [Mobility Radeon HD 3650] driver: radeon v: kernel bus-ID: 01:00.0 
           Device-2: Chicony 2M UVC Webcam type: USB driver: uvcvideo bus-ID: 1-2:3 
           Display: server: X.org 1.13.0 driver: loaded: ati,radeon unloaded: modesetting,vesa 
           resolution: <missing: xdpyinfo> 
           Message: Unable to show advanced data. Required tool glxinfo missing.  

Inxxi Mint:

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System:
  Host: compal Kernel: 5.4.0-58-generic x86_64 bits: 64 compiler: gcc 
  v: 9.3.0 Desktop: MATE 1.24.0 Distro: Linux Mint 20.1 Ulyssa 
  base: Ubuntu 20.04 focal 
Machine:
  Type: Laptop System: - product: N/A v: N/A 
  serial: <superuser/root required> 
  Mobo: - model: IFL90 v: IFT00 serial: <superuser/root required> 
  BIOS: COMPAL v: 1.18 date: 06/18/2008 
CPU:
  Topology: Dual Core model: Intel Core2 Duo T7500 bits: 64 type: MCP 
  arch: Core Merom rev: B L2 cache: 4096 KiB 
  flags: lm nx pae sse sse2 sse3 ssse3 vmx bogomips: 8777 
  Speed: 798 MHz min/max: 800/2201 MHz Core speeds (MHz): 1: 798 2: 798 
Graphics:
  Device-1: AMD RV635/M86 [Mobility Radeon HD 3650] driver: radeon v: kernel 
  bus ID: 01:00.0 
  Display: x11 server: X.Org 1.20.8 driver: ati,radeon 
  unloaded: fbdev,modesetting,vesa resolution: 1280x800~60Hz 
  OpenGL: renderer: AMD RV635 (DRM 2.50.0 / 5.4.0-58-generic LLVM 10.0.0) 
  v: 3.3 Mesa 20.0.8 direct render: Yes  

I also checked EDID and it looks the same as configuration on both linux distributions

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user@compal:~$ sudo get-edid | parse-edid
This is read-edid version 3.0.2. Prepare for some fun.
Attempting to use i2c interface
No EDID on bus 1
No EDID on bus 2
No EDID on bus 3
No EDID on bus 4
2 potential busses found: 0 5
Will scan through until the first EDID is found.
Pass a bus number as an option to this program to go only for that one.
Bus 0 doesn't really have an EDID...
128-byte EDID successfully retrieved from i2c bus 5
Looks like i2c was successful. Have a good day.
Checksum Correct

Section "Monitor"
	Identifier ""
	ModelName ""
	VendorName "CPT"
	# Monitor Manufactured week 38 of 2007
	# EDID version 1.3
	# Digital Display
	DisplaySize 330 210
	Gamma 2.20
	Option "DPMS" "false"
	Modeline 	"Mode 0" 68.90 1280 1312 1344 1408 800 801 804 816 -hsync -vsync 
EndSection
user@compal:~$ 

[Hoser Rob]

PartedMagic is not really seen as a distro as such, it's known as a disk rescue tool. But it does obviously have to have a Linux runtime environment, and according to your inxi output it's running the Openbox window manager as a desktop, and it's using a 3.5.0 Linux kernel.

That's an old kernel (it hasn't been supported since 2012) but that's an even older video card. I suspect that's the issue.

I haven't used AMD graphics for a while but I do know that there's no other driver for a 3xxx card than the one you have, no magic drivers there.

First I'd try disabling all desktop compositing. See the GUI method here: https://wiki.archlinux.org/index.php/MA ... ompositing ... I haven't used Mate for a while so I forget the menus, but it should be something very much like that.

You could also try downloading the Mint 19.2 Mate iso and testing that in a live USB stick boot. 19.2 uses the 4.15 series kernel, which is long term support and has better old hardware support. All later Mint releases use a >=5.0 kernel, which is not so good with old hardware.

[Maxxis]

I tried 19.2 and indeed it works correctly. It's a pity that in newer releases something is broken and old graphics card does not work correctly.
When I will use 19.2 will it be possible to enable system updates or there is risk that it would stop working properly when some updates would be installed ?

[SMG]

I tried 19.2 and indeed it works correctly. It's a pity that in newer releases something is broken and old graphics card does not work correctly.
When I will use 19.2 will it be possible to enable system updates or there is risk that it would stop working properly when some updates would be installed ?

The newer releases are not "broken". In order to keep the Linux kernel from growing exponentially in size, when drivers are added for newer equipment, some of the oldest drivers are removed. The drivers for your card have to come from the kernel.

LM19.2 uses the 4.15 kernel which, based on your comments, appears to have the drivers for your system. You can upgrade to LM19.3 and keep that 4.15 kernel. LM19 is supported for two more years.

[Maxxis]

I think that something is broken. Graphic card is correctly recognized. I still have image on new kernel, but it is broken on internal laptop screen. It works no problem on external monitor. If it would not recognize card, no graphic mode at all, no drivers etc. then we could say that this card is not supported.
This is not the case that card is not recognized and thus not supported. The problem is that support for internal laptop screen has some fault.
Did they remove support for laptop screen but kept support for external monitors ? That does not make sense.
I can report this bug on other web page since for sure this is not specific to Mint but I' don't know where.
Anyway, assuming that they intentionally removed support for laptop displays - this is wrong.
Although this is old laptop but it is not ancient and is able to run all modern web pages including youtube. It is powerful enough for everyday use.
I think that this is bad idea in Linux to include drivers inside kernel which would eventually grow indefinitely unless you would remove something what is still good enough to be used for everyday work.
Drivers should be included in separate files and loaded only when needed so only disk space would be consumed but not other resources. They could even remove those drivers from package to save disk space but should be still possible to download and install manually when needed.

[SMG]

Graphic card is correctly recognized. I still have image on new kernel, but it is broken on internal laptop screen. It works no problem on external monitor. If it would not recognize card, no graphic mode at all, no drivers etc. then we could say that this card is not supported.

I had forgotten it worked properly on the external display.

I am not aware of there being different drivers for internal displays versus external displays.

[Maxxis]

This is not problem with kernel.
After installation of 19.2 I installed updates and added few additional programs. Later suddenly I have again problems with screen. Kernel is 4.15.0-140-generic
I made Timeshift backup just after installation before changing anything so that I will try to revert to initial configuration and will try to find out what is corrupting configuration.

[SMG]

This is not problem with kernel.

You will have to test to determine that. You are using a different kernel version than the one which was on the LM19.2 ISO.

I believe that ISO has 4.15.0-53 or so (I do not recall the exact end numbers) and now you are using 4.15.0-140.

[Maxxis]

Yes, you're right. I should write: "this is not problem with 5.x kernel."
Initial kernel in 19.2 is 4.15.0-54-generic
I restored snapshot and it fixed graphic, when I installed updates and it is broken again. After updates kernel is 4.15.0-140-generic.
Now I will restore again and will install updates partially to verify which one cause problems.
Good that at lease it is possible to restore to working state so it should be possible to isolate problematic update package.

[SMG]

Good that at lease it is possible to restore to working state so it should be possible to isolate problematic update package.

If you can determine which package it might be (presuming it is not the kernel), then maybe there will be a way to figure out how to get it to work on LM20. Just a thought to keep in mind.

[Maxxis]

Unfortunately problem is in kernel update. If I select to be updated only package "linux-4.15.0.140.144" then after system restart image is corrupted. This package install also some additional required dependencies.

It will be difficult to find out what has changed although this seems to be very minor change in kernel version number.
Between 54 and 140 there is lot of numbers but perhaps it would be possible to load some versions with numbers between those two and finally find out exact release which introduce that bug and then check diff.
This however could be difficult for me since mintUpdate does not include those versions. It would have to be downloaded and installed manually.

[SMG]

This however could be difficult for me since mintUpdate does not include those versions. It would have to be downloaded and installed manually.

I thought Update Manager was available in LM19.2. Do you not have it? You should be able to see the available kernels in it.

I do not recall the changes in Update Manager between LM19.2 and the LM20 version I have. In LM20 one selects View > Linux Kernels and then clicks Continue. Then you would click 4.15 on the left pane and see the available kernels on the right pane.

I'll do a search on the changelog for 4.15.0-140 and see if I can determine what might be the issue and thus which kernel to try.

[SMG]

I'll do a search on the changelog for 4.15.0-140 and see if I can determine what might be the issue and thus which kernel to try.

I searched through the 4.15.0-141 Changelog, which has the specific changes for that kernel and all the ones which preceded it, for the word radeon and here the changes listed for kernels higher than 4.15.0-54. The number at the left is the kernel patch number.

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129 -   * [HP 635] Radeon 6310 brightness control does not work (LP: #1894667) //
    Bionic update: upstream stable patchset 2020-11-18 (LP: #1904791)
    - ACPI: video: use ACPI backlight for HP 635 Notebook

119 - drm/radeon: fix multiple reference count leak
    - drm/radeon: Fix reference count leaks caused by pm_runtime_get_sync
    - drm/radeon: fix array out-of-bounds read and write issues
    - drm/radeon: disable AGP by default

113 - drm/radeon: fix double free
    - drm/radeon: fix fb_div check in ni_init_smc_spll_table()
    - MIPS: Loongson: Build ATI Radeon GPU driver as module

97  - radeon: insert 10ms sleep in dce5_crtc_load_lut

89  - drm/radeon: fix bad DMA from INTERRUPT_CNTL2

87  - drm/radeon: fix r1xx/r2xx register checker for POT textures

73  - drm/radeon: fix si_enable_smc_cac() failed issue

71  - Revert "drm/radeon: Fix EEH during kexec"
    - drm/radeon: Bail earlier when radeon.cik_/si_support=0 is passed

67  - drm/radeon: Fix EEH during kexec
    - gpu: drm: radeon: Fix a possible null-pointer dereference in
      radeon_connector_set_property()

59  - PCI: Mark AMD Stoney Radeon R7 GPU ATS as broken
    - drm/radeon/evergreen_cs: fix missing break in switch statement
    - gpu: drm: radeon: Set DPM_FLAG_NEVER_SKIP when enabling PM-runtime

55  * ubuntu 18.04 flickering screen with Radeon X1600 (LP: #1791312)
    - drm/radeon: prefer lower reference dividers

Notice that --71 has a reversal of what was done in --67.

I do not know enough about the specific card you are using to know which might be the specific change affecting it, or even if it is a radeon change which is causing the problem. It's possible the microcode change is the issue. Hopefully, the searching I did will be of some help.

[Hoser Rob]

I tried 19.2 and indeed it works correctly. It's a pity that in newer releases something is broken and old graphics card does not work correctly.
When I will use 19.2 will it be possible to enable system updates or there is risk that it would stop working properly when some updates would be installed ?

The newer releases are not "broken". ....

Ummm .. yes, they ARE broken.

[Maxxis]

I tested several kernel versions (55, 60, 70, 101, 140) and it look like bug has been introduced in kernel 4.15.0-55-generic. All tested kernels starting with 55 have screen bug present.
I have collected logs with kernel 54 and 55. Since in logs fault is not visible, if there would be required some proof of existing fault I also recorded video which shows working system on kernel 55 with internal laptop LCD and external LCD.
With those information would it be possible to report this bug to kernel team so hopefully this could be fixed in future ?

[SMG]

With those information would it be possible to report this bug to kernel team so hopefully this could be fixed in future ?

There is a link to report bugs for a specific kernel within Update Manager for LM20.

Here are directions to get to it for LM20. (I do not have an LM19 install available, so the steps might not be exactly the same.)
-- Open Update Manager.
-- Select View > Linux Kernels and click Continue.
-- In the left pane, make sure 4.15 is selected.
-- The right pane will list all the available 4.15 kernels. Click 4.15.0-55-generic.
-- The first link under the kernel number is "Bug Reports". Click it to open a web page with the bugs reported on that kernel.
-- On the right side of the page near the top is a button to "Report a Bug".

[Maxxis]

It seems that the same problem is already reported but for Radeon HD3450.
https://bugs.launchpad.net/ubuntu/+sour ... ug/1861554

[SMG]

Within the comments on that link is a link to this Radeon mobility HD3450 (RV620) heavy screen flickering after trying to upgrade kernel 4.15.0-54 where the maintainer Alex Deucher indicates, "The problem is the patch fixed the exact same problem for someone else. So we'd just be trading one bug for another. We'd need to be able to test any solutions on both problematic systems." That comment was posted a year ago.

There is a "patch" listed in the last post in that thread, but I do not understand how one applies it, so I can not help with that.