Arch Linux

Balto

Member

Registered: 2014-11-22

Posts: 7

RandR resolution issue after update

After updating yesterday I've experienced a strange issue with applying RandR mode settings.

I have a laptop (Clevo W230ST, Intel GT2 IGPU) with an internal eDP and a VGA connected to a 1600x900 desktop monitor. The EDID on the VGA is not available for some reason, so I add the resolution in xrandr with a modeline from cvt. This used to work without problem.

After yesterday's update, when I try to apply the created and added mode with something like xrandr --output VGA1 --mode 1600x900R, the screens will be flicking for a short while and then the VGA would go back to the default resolution (768p). If I change the mode to any of the fail-safe resolutions (480p, 600p, 1024p), it would work. If I choose any that's created with a cvt modeline, it would go back to 768p.

The applied mode does appear to take effect, but only for a fraction of a second. If I try to apply a supported resolution there's a small chance I can see the monitor displaying the correct aspect ratio before turning black and going back to 4:3 1024x768 again. If I deliberately create and apply a unsupported resolution I might see the monitor giving a "resolution not supported" warning, but again only for a fraction of a second before it goes back.

I've also noticed strong flicking on the eDP monitor when adding or applying modes to the VGA, which if I recall correctly was not experienced before.

XRandR does not give and error or warning when I do what's described above. I've checked the recent pacman log and Arch news but found nothing interesting.

Is there any known bug/regression related to this recently?

Last edited by Balto (2014-11-22 13:43:31)

Balto

Member

Registered: 2014-11-22

Posts: 7

Re: RandR resolution issue after update

Bump. Anyone experiencing similar issues?

Edit: I borrowed another display with VGA input for testing, which can get EDIE recognized correctly and work accordingly when connected to the laptop with a compatible VGA cable. I recorded the display mode parameters based on the EDID and saved it as a new mode, and when I switch to another cable that doesn't transmit EDIE information, the exactly same configurations fails.

Connected via EDIE-compatible cable:

$ xrandr --verbose
      ... 
  1920x1080 (0x158) 148.500MHz +HSync +VSync *current +preferred
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
      ...
$ xrandr --newmode 1080P 148.500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
$ xrandr --addmode VGA1 1080P
$ xrandr --verbose
      ... 
  1920x1080 (0x158) 148.500MHz +HSync +VSync *current +preferred
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
      ...
  1080P (0x173) 148.500MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
      ...
$ xrandr --output VGA1 --mode 1024x768               # switch to a different res first to make sure the new mode is indeed applied successfully
$ xrandr --output VGA1 --mode 1080P                  # works as expected

Now switch to EDID-incompatible VGA cable:

$ xrandr --verbose
      ... 
  1080P (0x173) 148.500MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
      ...
$ xrandr --output VGA1 --mode 1080P                  # DOES NOT WORK, fall back to 1024x768 after heavy flickering

Is there some kind of better-safe-than-sorry validation going on?

I've noticed similar problems on another Fedora 21 box now, so this is not distro-specific.

Edit2: It's a Gnome problem. Can't pin-point what's causing the issue, so I'm abandoning Gnome for now.

Last edited by Balto (2015-01-14 20:59:45)