Display size detected incorrectly

[Dark Dragon]

My external monitor is detected as 7" although it is 32". All applications which use Qt auto scaling have huge controls!

It seems like many users have the same problem (https://ubuntuforums.org/showthread.php?t=2390362) and thus disable Qt auto scaling. I think the solution should be to fix the size detection instead.

It seems not related to the display server, compositor or window manager since the problem appeared in Ubuntu 17.04 (Mir, Unity) as well es 18.04 (Mutter, Gnome). I tried it with both Wayland and X (on Wayland).

Further, it seems not related to graphics driver, since I personally use the open source driver with my internal Intel card, whereas someone else uses a proprietary Nvidia driver (https://askubuntu.com/q/1066879/206608).

If it is in the wrong category, please move it / add the corresponding packages.

If you need any further information to tackle the problem, just tell me!
---
ProblemType: Bug
ApportVersion: 2.20.9-0ubuntu7.3
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
DistroRelease: Ubuntu 18.04
InstallationDate: Installed on 2017-09-05 (372 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
Package: qtbase-opensource-src
PackageArchitecture: amd64
Tags: bionic
Uname: Linux 4.18.7-041807-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom davfs2 dip docker lpadmin plugdev sambashare sudo vboxusers video voice
_MarkForUpload: True

[Sebastian Ramacher (s-ramacher)]

Broken auto-scaling is a bug in Qt. If your monitor is incorrectly detected as 7", there's probably also a kernel or X.org bug somewhere.

[Daniel van Vugt (vanvugt)]

Thanks for the bug report.

1. Can you please run this command on the machine and send us the output?

  xrandr --verbose

2. Please also run this command to send more system information:

  apport-collect 1792167

[Dark Dragon (darkdragon-001)]

apport information

[Dark Dragon (darkdragon-001)]

apport information

[Dark Dragon (darkdragon-001)]

apport information

[Dark Dragon (darkdragon-001)]

1. xrandr

I generated the output and attached the section for the external display. I guess the first line already shows the problem:

    HDMI-1 connected 1920x1080+1366+0 (0x8b) normal (normal left inverted right x axis y axis) 160mm x 90mm

It includes "160mm x 90mm" which probably translates to 7".

2. apport

I generated the requested log. I installed Ubuntu 17.04, upgraded to 17.10 and now upgraded to 18.04. I use the latest kernel from kernel.ubuntu.com.

[Dark Dragon (darkdragon-001)]

Same result when I connect via DP->HDMI adapter

[Dark Dragon (darkdragon-001)]

I booted up a live disk with Ubuntu 17.04 (Unity) and it shows the same behavior.

[Dark Dragon (darkdragon-001)]

Do you need any additional information?

[psypher (psypher246)]

ProblemType: Bug
ApportVersion: 2.20.9-0ubuntu7.4
Architecture: amd64
CurrentDesktop: GNOME
DistroRelease: Ubuntu 18.04
InstallationDate: Installed on 2017-04-08 (556 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
Package: qtbase-opensource-src
PackageArchitecture: amd64
ProcVersionSignature: Ubuntu 4.15.0-36.39-generic 4.15.18
Tags: third-party-packages bionic
Uname: Linux 4.15.0-36-generic x86_64
UpgradeStatus: Upgraded to bionic on 2018-10-16 (0 days ago)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
_MarkForUpload: True

[psypher (psypher246)]

apport information

[psypher (psypher246)]

apport information

[psypher (psypher246)]

apport information

[psypher (psypher246)]

Hi having the same issue since upgrading from 16.04 to 18.04. My LG 34" (Model 34UM68-P) is only detecting 1920x1080@16:9 where is should be 2560x1080@21:9. xrandr attached

[Launchpad Janitor (janitor)]

[Expired for qtbase-opensource-src (Ubuntu) because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for mutter (Ubuntu) because there has been no activity for 60 days.]

[Martend (martend-baas)]

Bug still present. In my multi-display setup a 40" display is reported as a 7" in Ubuntu.

[Daniel van Vugt (vanvugt)]

Sorry I lost track of this bug. The attachment in comment #7 shows:

HDMI-1 connected 1920x1080+1366+0 (0x8b) normal (normal left inverted right x axis y axis) 160mm x 90mm

So the hardware is indeed reporting itself as ~7.2 inches. This is a hardware fault (incorrect EDID data?) I have seen before. Probably the best we can hope for is to add heuristics to detect faulty hardware, but that would be unreliable and unlikely to ever happen.

[Dark Dragon (darkdragon-001)]

How can I check if the hardware is really sending faulty data or if it is just incorrectly parsed?

[Daniel van Vugt (vanvugt)]

To be absolutely sure you would need to:

1. Convert the display's EDID into binary from hex:

  00ffffffffffff004c2d090501000000
  30120103801009780aee91a3544c9926
  0f5054bdef80714f8100814081809500
  950fb3000101023a801871382d40582c
  4500a05a0000001e662150b051001b30
  40703600a05a0000001e000000fd0018
  4b1a5117000a202020202020000000fc
  0053414d53554e470a2020202020016f
  020327f14b901f041305140312202122
  2309070783010000e2000fe305030167
  030c001000b82d011d007251d01e206e
  285500a05a0000001e011d00bc52d01e
  20b8285540a05a0000001e011d801871
  1c1620582c2500a05a0000009e011d80
  d0721c1620102c2580a05a0000009e00
  0000000000000000000000000000001d

2. Use an EDID decoding tool to verify it yourself. Some are available in the Ubuntu archive, but also you can google for online EDID decoders.

[Daniel van Vugt (vanvugt)]

Here I've decoded your EDID using 'xxd' and then 'edid-decode':

EDID version: 1.3
Manufacturer: SAM Model 509 Serial Number 1
Made in week 48 of 2008
Digital display
Maximum image size: 16 cm x 9 cm
Gamma: 2.20
RGB color display
First detailed timing is preferred timing
Display x,y Chromaticity:
  Red: 0.6396, 0.3300
  Green: 0.2998, 0.5996
  Blue: 0.1503, 0.0595
  White: 0.3125, 0.3291
Established timings supported:
  720x400@70Hz 9:5 HorFreq: 31469 Hz Clock: 28.320 MHz
  640x480@60Hz 4:3 HorFreq: 31469 Hz Clock: 25.175 MHz
  640x480@67Hz 4:3 HorFreq: 35000 Hz Clock: 30.240 MHz
  640x480@72Hz 4:3 HorFreq: 37900 Hz Clock: 31.500 MHz
  640x480@75Hz 4:3 HorFreq: 37500 Hz Clock: 31.500 MHz
  800x600@60Hz 4:3 HorFreq: 37900 Hz Clock: 40.000 MHz
  800x600@72Hz 4:3 HorFreq: 48100 Hz Clock: 50.000 MHz
  800x600@75Hz 4:3 HorFreq: 46900 Hz Clock: 49.500 MHz
  832x624@75Hz 4:3 HorFreq: 49726 Hz Clock: 57.284 MHz
  1024x768@60Hz 4:3 HorFreq: 48400 Hz Clock: 65.000 MHz
  1024x768@70Hz 4:3 HorFreq: 56500 Hz Clock: 75.000 MHz
  1024x768@75Hz 4:3 HorFreq: 60000 Hz Clock: 78.750 MHz
  1280x1024@75Hz 5:4 HorFreq: 80000 Hz Clock: 135.000 MHz
  1152x870@75Hz 192:145 HorFreq: 67500 Hz Clock: 108.000 MHz
Standard timings supported:
  1152x864@75Hz 4:3 HorFreq: 67500 Hz Clock: 108.000 MHz
  1280x800@60Hz 16:10
  1280x960@60Hz 4:3 HorFreq: 60000 Hz Clock: 108.000 MHz
  1280x1024@60Hz 5:4 HorFreq: 64000 Hz Clock: 108.000 MHz
  1440x900@60Hz 16:10 HorFreq: 55500 Hz Clock: 88.750 MHz
  1440x900@75Hz 16:10 HorFreq: 82300 Hz Clock: 156.000 MHz
  1680x1050@60Hz 16:10 HorFreq: 64700 Hz Clock: 119.000 MHz
Detailed mode: Clock 148.500 MHz, 160 mm x 90 mm
               1920 2008 2052 2200 hborder 0
               1080 1084 1089 1125 vborder 0
               +hsync +vsync
               VertFreq: 60 Hz, HorFreq: 67500 Hz
Detailed mode: Clock 85.500 MHz, 160 mm x 90 mm
               1360 1424 1536 1792 hborder 0
                768 771 777 795 vborder 0
               +hsync +vsync
               VertFreq: 60 Hz, HorFreq: 47712 Hz
Monitor ranges (GTF): 24-75Hz V, 26-81kHz H, max dotclock 230MHz
Monitor name: SAMSUNG
Has 1 extension blocks
Checksum: 0x6f (valid)

CTA extension block
Extension version: 3
35 bytes of CTA data
  Video data block
    VIC 16 1920x1080@60Hz 16:9 (native) HorFreq: 67500 Hz Clock: 148.500 MHz
    VIC 31 1920x1080@50Hz 16:9 HorFreq: 56250 Hz Clock: 148.500 MHz
    VIC 4 1280x720@60Hz 16:9 HorFreq: 45000 Hz Clock: 74.250 MHz
    VIC 19 1280x720@50Hz 16:9 HorFreq: 37500 Hz Clock: 74.250 MHz
    VIC 5 1920x1080i@60Hz 16:9 HorFreq: 33750 Hz Clock: 74.250 MHz
    VIC 20 1920x1080i@50Hz 16:9 HorFreq: 28125 Hz Clock: 74.250 MHz
    VIC 3 720x480@60Hz 16:9 HorFreq: 31469 Hz Clock: 27.000 MHz
    VIC 18 720x576@50Hz 16:9 HorFreq: 31250 Hz Clock: 27.000 MHz
    VIC 32 1920x1080@24Hz 16:9 HorFreq: 27000 Hz Clock: 74.250 MHz
    VIC 33 1920x1080@25Hz 16:9 HorFreq: 28125 Hz Clock: 74.250 MHz
    VIC 34 1920x1080@30Hz 16:9 HorFreq: 33750 Hz Clock: 74.250 MHz
  Audio data block
    Linear PCM, max channels 2
      Supported sample rates (kHz): 48 44.1 32
      Supported sample sizes (bits): 24 20 16
  Speaker allocation data block
  ...

[Dark Dragon (darkdragon-001)]

Thanks a lot! I will investigate ways to correct this information: https://github.com/linuxhw/EDID/issues/4