Bug 22853

Created attachment 27852 [details]
Xorg.0.log

Created attachment 27853 [details]
xorg.conf

Created attachment 27854 [details]
xrandr output

Your monitor's edid is the problem.  It's limiting the modes since it specifies a max pix clock of 110 Mhz and the pix clock of the 1280x1024 mode is 135 Mhz:

(II) RADEON(0): 1280x1024@75Hz
Modeline "1280x1024"x0.0  135.00  1280 1296 1440 1688  1024 1025 1028 1066 +hsync +vsync (80.0 kHz)
Ranges: V min: 50 V max: 120 Hz, H min: 30 H max: 72 kHz, PixClock max 110 MHz

To override, you need to specify the modeline for the preferred mode in your xorg.conf monitor section, e.g.,:

Modeline "1280x1024"  135.00  1280 1296 1440 1688  1024 1025 1028 1066 +hsync +vsync
Option "PreferredMode" "1280x1024"

You can also manually add the modeline at runtime with xrandr:
xrandr --newmode "1280x1024"  135.00  1280 1296 1440 1688  1024 1025 1028 1066 +hsync +vsync
xrandr --addmode VGA-0 "1280x1024"
xrandr --output VGA-0 --mode "1280x1024"

If the 1280x1024 mode works, then we probably need an edid quirk for your monitor in the xserver.

Well:
- according to its specs, Acer 77e can do 1280x1024@67Hz
- 1280x1024 did was supported with the SiS driver with this Acer

AFAIC, there's two bugs in ati driver:
- when a mode is not supported, it should be written down in
  the logs, thus it's easier to understand the issues
- we should select alesser refresh frequency when the suggested
  one is too high.

(In reply to comment #5)
> Well:
> - according to its specs, Acer 77e can do 1280x1024@67Hz
> - 1280x1024 did was supported with the SiS driver with this Acer
> 

The monitor's edid does not contain an modeline for 1280x1024@67hz, as such you'd need to add a modeline to use it.  The edid does contain a a 1280x1024@75hz mode, however it conflicts with the max pixclock specified in the same edid.  So either the max pixclock is wrong or the the 1280x1024@75hz mode shouldn't be there.  If the 1280x1024@75hz mode does work, then an edid quirk needs to be added to the xserver.

> AFAIC, there's two bugs in ati driver:
> - when a mode is not supported, it should be written down in
>   the logs, thus it's easier to understand the issues

This is handled by the common randr code in the xserver, not the driver.  If you enable more verbose server logging you can see which modes get rejected and why.

> - we should select alesser refresh frequency when the suggested
>   one is too high.
> 

You'll need to specify an modeline if you want to use a mode that's not in the monitor's edid.  It's not really feasible to add every possible mode to the output there are just too many possibilities.  Plus, most monitors (especially LCDs) are very picky about what mode timings they will accept.

Created attachment 28185 [details] [review]
Xorg.0.log with 6.12.99 snapshot

With a git snapshot, this bug is somewhat "fixed" (because getting EDID failed or wasn't performed)

Mass closure: This bug has been untouched for more than six years, and is not obviously still valid. Please file a new report if you continue to experience issues with a current server.