Probably related:
https://patchwork.kernel.org/patch/9716467/
Since the introduction of kernel 4.8 I've been experiencing color
banding on my Lenovo G50-80 notebook. I also had reports of the same
symptoms on the G50-70 model.
I figured out that the problem had been introduced by commit
210a021dab639694600450c14b877bf3e3240adc
The G50-80's LCD panel supports 6bpc, but is now set to 8bpc,
and the system probably falls back to 6bpc
without any dithering, which result in heavily banded gradients.
I fixed it for myself by adding an EDID quirk for that particular LCD
panel (see the attached patch). It's unknown to me, however, if there
are any other panels affected by the issue, so maybe a more general
solution might be desirable.
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index fad3d44e4642..ee3124bcae87 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -147,6 +147,9 @@ static const struct edid_quirk {
/* Medion MD 30217 PG */
{ "MED", 0x7b8, EDID_QUIRK_PREFER_LARGE_75 },
+ /* Fix for Lenovo G50 */
+ { "SDC", 18514, EDID_QUIRK_FORCE_6BPC },
+
/* Panel in Samsung NP700G7A-S01PL notebook reports 6bpc */
{ "SEC", 0xd033, EDID_QUIRK_FORCE_8BPC },
** Tags added: banding bionic color edid i915 lenovo-g50
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Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1819968
Title:
Colour banding in Lenovo G50-80 laptop display (i915)
Status in linux package in Ubuntu:
Incomplete
Bug description:
Colour bandind is visible everywhere in the system. I believe it's not
a hardware problem, since booting with 'nomodeset' works as expected
and the previously installed Ubuntu 14.04 also worked.
I tried installing kernel 4.18.0-16.17 from ppa:canonical-kernel-
team/ppa but the problem remained.
There were already similar bugs,
https://bugs.launchpad.net/bugs/1749420 ,
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1794387 and
https://bugs.launchpad.net/bugs/1788308, but the fixes provided for
those bugs did not work for my specific monitor.
cat /proc/version_signature
Ubuntu 4.15.0-46.49-generic 4.15.18
sudo lspci -vnvn
00:00.0 Host bridge [0600]: Intel Corporation Haswell-ULT DRAM Controller
[8086:0a04] (rev 0b)
Subsystem: Lenovo Haswell-ULT DRAM Controller [17aa:390b]
Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort+ >SERR- <PERR- INTx-
Latency: 0
Capabilities: [e0] Vendor Specific Information: Len=0c <?>
Kernel driver in use: hsw_uncore
00:02.0 VGA compatible controller [0300]: Intel Corporation Haswell-ULT
Integrated Graphics Controller [8086:0a16] (rev 0b) (prog-if 00 [VGA
controller])
Subsystem: Lenovo Haswell-ULT Integrated Graphics Controller [17aa:390b]
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx+
Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort- >SERR- <PERR- INTx-
Latency: 0
Interrupt: pin A routed to IRQ 46
Region 0: Memory at b0000000 (64-bit, non-prefetchable) [size=4M]
Region 2: Memory at a0000000 (64-bit, prefetchable) [size=256M]
Region 4: I/O ports at 4000 [size=64]
[virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
Address: fee02004 Data: 4023
Capabilities: [d0] Power Management version 2
Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA
PME(D0-,D1-,D2-,D3hot-,D3cold-)
Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [a4] PCI Advanced Features
AFCap: TP+ FLR+
AFCtrl: FLR-
AFStatus: TP-
Kernel driver in use: i915
Kernel modules: i915
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