Xorg display refresh rate settings inaccurate or too conservative

[Obi Bok]

Binary package hint: xserver-xorg

When going through many filed bugs (#77037, #63026, #61614, #47234, #42880) and forum posts I noticed that many users experience problems with display resolutions and refresh rates set in Xorg. Usually, simply increasing the H/V sync range fixes these issues.

I myself tested this on a BenQ FP731 LCD. Xorg sets HorizSync=28-64, VertRefresh=43-60; while the actual values as per the display manual are 28-81/43-76.

Perhaps Xorg sets these values in a too conservative way, based on the belief that it could damage old CRT monitors? How about implementing an option to extend the range of frequencies?

[Bryce Harrington (bryce)]

Yes, the heuristics in xserver-xorg.postinst.in are approximate at best, and make a number of rather ambitious assumptions. These often work correctly, but sometimes result in bugs such as those reported.

Anecdotal evidence suggests that xorg itself (with no xorg.conf) can do a better job of detection in these circumstances, however this remains to be tested.