Comment 42 for bug 1761751

Some information from me, using 4.16.8 kernel
System is Lenovo Z50-75 laptop with AMD-A10 cpu (Kaveri) and both HDMI and VGA ports. I use the VGA port to which is connected an Acer X223HQ display, capable of displaying up to 1920x1080. The laptop screen is also 1920x1080

If system is booted with the following kernel options

amdgpu.cik_support=1 radeon.cik_support=0 amdgpu.dc=1

I get a black/blank VGA screen.

If system is booted with

amdgpu.cik_support=1 radeon.cik_support=0 amdgpu.dc=0

I get a working VGA display in addition to the laptop screen.

With amdgpu.dc=1 the contents of /sys/class/drm are:
card0
card0-eDP-1
card0-HDMI-A-1
renderD128
ttm
version

With amdgpu.dc=0 the contents of /sys/class/drm are:
card0
card0-eDP-1
card0-HDMI-A-1
card0-VGA-1
renderD128
ttm
version

With amdgpu.dc=0, dmesg lines containing 'drm' are

[ 1.749135] [drm] radeon kernel modesetting enabled.
[ 1.750430] fb: switching to radeondrmfb from EFI VGA
[ 1.795937] [drm] amdgpu kernel modesetting enabled.
[ 1.804524] [drm] initializing kernel modesetting (KAVERI 0x1002:0x130A 0x17AA:0x3988 0x00).
[ 1.804544] [drm] register mmio base: 0xF0B00000
[ 1.804547] [drm] register mmio size: 262144
[ 1.828764] [drm] BIOS signature incorrect 0 0
[ 1.829561] [drm] vm size is 64 GB, 2 levels, block size is 10-bit, fragment size is 9-bit
[ 1.829586] [drm] Detected VRAM RAM=1024M, BAR=1024M
[ 1.829589] [drm] RAM width 64bits UNKNOWN
[ 1.829727] [drm] amdgpu: 1024M of VRAM memory ready
[ 1.829731] [drm] amdgpu: 3072M of GTT memory ready.
[ 1.829747] [drm] GART: num cpu pages 262144, num gpu pages 262144
[ 1.829797] [drm] PCIE GART of 1024M enabled (table at 0x000000F400040000).
[ 1.829885] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[ 1.829888] [drm] Driver supports precise vblank timestamp query.
[ 1.829920] [drm] Internal thermal controller without fan control
[ 1.829923] [drm] amdgpu: dpm initialized
[ 1.830640] [drm] amdgpu atom DIG backlight initialized
[ 1.830644] [drm] AMDGPU Display Connectors
[ 1.830647] [drm] Connector 0:
[ 1.830649] [drm] VGA-1
[ 1.830651] [drm] HPD2
[ 1.830654] [drm] DDC: 0x1950 0x1950 0x1951 0x1951 0x1952 0x1952 0x1953 0x1953
[ 1.830657] [drm] Encoders:
[ 1.830659] [drm] CRT1: INTERNAL_UNIPHY2
[ 1.830661] [drm] CRT1: NUTMEG
[ 1.830663] [drm] Connector 1:
[ 1.830665] [drm] HDMI-A-1
[ 1.830667] [drm] HPD3
[ 1.830670] [drm] DDC: 0x1954 0x1954 0x1955 0x1955 0x1956 0x1956 0x1957 0x1957
[ 1.830673] [drm] Encoders:
[ 1.830675] [drm] DFP1: INTERNAL_UNIPHY2
[ 1.830677] [drm] Connector 2:
[ 1.830679] [drm] eDP-1
[ 1.830681] [drm] HPD1
[ 1.830684] [drm] DDC: 0x194c 0x194c 0x194d 0x194d 0x194e 0x194e 0x194f 0x194f
[ 1.830687] [drm] Encoders:
[ 1.830690] [drm] LCD1: INTERNAL_UNIPHY
[ 1.831974] [drm] Found UVD firmware Version: 1.55 Family ID: 9
[ 1.832424] [drm] Found VCE firmware Version: 50.10 Binary ID: 2
[ 1.923930] [drm] UVD initialized successfully.
[ 2.042436] [drm] VCE initialized successfully.
[ 3.097431] [drm] fb mappable at 0xA0428000
[ 3.097436] [drm] vram apper at 0xA0000000
[ 3.097438] [drm] size 8294400
[ 3.097440] [drm] fb depth is 24
[ 3.097442] [drm] pitch is 7680
[ 3.098563] fbcon: amdgpudrmfb (fb0) is primary device
[ 6.593703] amdgpu 0000:00:01.0: fb0: amdgpudrmfb frame buffer device
[ 6.610690] [drm] Initialized amdgpu 3.23.0 20150101 for 0000:00:01.0 on minor 0

With amdgpu.dc=1, dmesg lines containing drm are:
[ 1.768255] [drm] radeon kernel modesetting enabled.
[ 1.770696] fb: switching to radeondrmfb from EFI VGA
[ 1.816131] [drm] amdgpu kernel modesetting enabled.
[ 1.824756] [drm] initializing kernel modesetting (KAVERI 0x1002:0x130A 0x17AA:0x3988 0x00).
[ 1.824788] [drm] register mmio base: 0xF0B00000
[ 1.824791] [drm] register mmio size: 262144
[ 1.849601] [drm] BIOS signature incorrect 0 0
[ 1.849724] [drm] vm size is 64 GB, 2 levels, block size is 10-bit, fragment size is 9-bit
[ 1.849746] [drm] Detected VRAM RAM=1024M, BAR=1024M
[ 1.849749] [drm] RAM width 64bits UNKNOWN
[ 1.850061] [drm] amdgpu: 1024M of VRAM memory ready
[ 1.850065] [drm] amdgpu: 3072M of GTT memory ready.
[ 1.850080] [drm] GART: num cpu pages 262144, num gpu pages 262144
[ 1.850131] [drm] PCIE GART of 1024M enabled (table at 0x000000F400040000).
[ 1.850256] [drm] Internal thermal controller without fan control
[ 1.850260] [drm] amdgpu: dpm initialized
[ 1.851672] [drm] Found UVD firmware Version: 1.55 Family ID: 9
[ 1.852176] [drm] Found VCE firmware Version: 50.10 Binary ID: 2
[ 1.854405] [drm:construct [amdgpu]] *ERROR* construct: Invalid Connector ObjectID from Adapter Service for connector index:3! type 0 expected 3
[ 1.854493] [drm:construct [amdgpu]] *ERROR* construct: Invalid Connector ObjectID from Adapter Service for connector index:4! type 0 expected 3
[ 1.854580] [drm:construct [amdgpu]] *ERROR* construct: Invalid Connector ObjectID from Adapter Service for connector index:5! type 0 expected 3
[ 1.854712] [drm:construct [amdgpu]] *ERROR* construct: Invalid Connector ObjectID from Adapter Service for connector index:6! type 0 expected 3
[ 1.868241] [drm] Display Core initialized with v3.1.27!
[ 1.875072] [drm] SADs count is: -2, don't need to read it
[ 1.875489] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[ 1.875495] [drm] Driver supports precise vblank timestamp query.
[ 1.894599] [drm] UVD initialized successfully.
[ 2.021094] [drm] VCE initialized successfully.
[ 2.050782] [drm] fb mappable at 0xA042A000
[ 2.050792] [drm] vram apper at 0xA0000000
[ 2.050795] [drm] size 8294400
[ 2.050798] [drm] fb depth is 24
[ 2.050801] [drm] pitch is 7680
[ 2.050938] fbcon: amdgpudrmfb (fb0) is primary device
[ 2.121174] amdgpu 0000:00:01.0: fb0: amdgpudrmfb frame buffer device
[ 2.146779] [drm] Initialized amdgpu 3.23.0 20150101 for 0000:00:01.0 on minor 0