lost screen resolution after Debian/Jessie upgrade
 

After update/upgrade within Debian/Jessie (affecting some 50 packages) and a reboot (after an uptime of about a month), the full resolution 2560x1440 of my Dell U2713HM has gone. xrandr is listing at most 1920x1200.

Given the long history of my installation, I tried a radical cure, purging all xorg related packages, and reinstalling them. No effect, still limited to 1920x1200.

Then I tried

~$ cvt 2560 1440
# 2560x1440 59.96 Hz (CVT 3.69M9) hsync: 89.52 kHz; pclk: 312.25 MHz
Modeline "2560x1440_60.00" 312.25 2560 2752 3024 3488 1440 1443 1448 1493 -hsync +vsync
~$ xrandr --newmode "2560x1440" 312.25 2560 2752 3024 3488 1440 1443 1448 1493 -hsync +vsync
~$ xrandr --addmode HDMI1 2560x1440
~$ xrandr --output HDMI1 --mode 2560x1440
xrandr: Configure crtc 0 failed

The only trace of this in Xorg.0.log is the following:

[ 3263.882] (II) intel(0): Allocated new frame buffer 2560x1440 stride 10240, tiled
[ 3264.048] (EE) intel(0): failed to set mode: Invalid argument
[ 3264.080] (II) intel(0): Allocated new frame buffer 1920x1200 stride 7680, tiled

According to lspci -v, my video device is the following:

00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06) (prog-if 00 [VGA controller])
Subsystem: Fujitsu Technology Solutions Device 11e7
Flags: bus master, fast devsel, latency 0, IRQ 46
Memory at f7800000 (64-bit, non-prefetchable) [size=4M]
Memory at e0000000 (64-bit, prefetchable) [size=256M]
I/O ports at f000 [size=64]
Expansion ROM at <unassigned> [disabled]
Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
Capabilities: [d0] Power Management version 2
Capabilities: [a4] PCI Advanced Features
Kernel driver in use: i915

Since I installed the full xorg dependency package, missing drivers is not a likely explanation.

Old and new log files at http://apps.jcns.fz-juelich.de/tmp/xorg-posting/.

NB: double posting with http://unix.stackexchange.com/questi...jessie-upgrade, which seems to attract very little views. Following advice given there, I also went to the xorg mailing list.

It's a driver bug.
 

The thread https://bbs.archlinux.org/viewtopic.php?id=179120 indicates some recently introduced problem with the Intel driver.

As was to be expected from that discussion, the problem only occurs with DVI cable. After switching to a DisplayPort cable, my full resolution was back.