Bug 17351 - xorg.conf keyword vscan is ignored
xorg.conf keyword vscan is ignored
Status: NEW
Product: xorg
Classification: Unclassified
Component: Server/DDX/Xorg
7.3 (2007.09)
Other All
: medium normal
Assigned To: Xorg Project Team
Xorg Project Team
:
Depends on:
Blocks:
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Reported: 2008-08-29 03:25 UTC by Peter D.
Modified: 2008-08-30 17:49 UTC (History)
0 users

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Description Peter D. 2008-08-29 03:25:49 UTC
According to "man xorg.conf" "vscan 2" should be the equivalent of "doublescan".  It is not.  

As for using "vscan 3", that seems right out of the question.  

Here is a small piece of my xorg.conf file.  

[snip]
    Option "ModeDebug" "True"
[snip]
# 640x481 119.29 Hz (CVT) hsync: 61.91 kHz; pclk: 52.50 MHz
Modeline "640x481_120.00"   52.50  640 680 744 848  481 484 494 519 -hsync +vsync
Modeline "640x482D_60.00"   52.50  640 680 744 848  482 485 495 520 -hsync +vsync doublescan
Modeline "640x483D_60.00"   52.50  640 680 744 848  483 486 496 521 -hsync +vsync vscan 2
[snip]

The second and third modelines are just hand edited variations on the first, which was generated by "cvt".  

And a small piece of /var/log/Xorg.0.log.  

[snip]
(II) RADEON(0): Modeline "640x483D_60.00"x59.4   52.50  640 680 744 848  483 486 496 521 vscan 2 -hsync +vsync (61.9 kHz)
(II) RADEON(0): Modeline "640x482D_60.00"x59.5   52.50  640 680 744 848  482 485 495 520 doublescan -hsync +vsync (61.9 kHz)
(II) RADEON(0): Modeline "640x481_120.00"x119.3   52.50  640 680 744 848  481 484 494 519 -hsync +vsync (61.9 kHz)
(II) RADEON(0): Modeline "640x480"x84.6   35.00  640 664 728 816  480 483 487 507 -hsync +vsync (42.9 kHz)
(II) RADEON(0): Modeline "640x480"x60.0   25.20  640 656 752 800  480 490 492 525 -hsync -vsync (31.5 kHz)
[snip]

The "vscan 2" makes its way into the log file - so it is apparently being parsed correctly, but it is ignored.  

Using krandr on KDE 4.1 selecting 640x483 should produce almost exactly the same results as selecting 640x482.  It does not.  The monitor reports the horizontal sync of one is twice that of the other.
Comment 1 Peter D. 2008-08-30 17:49:10 UTC
Sorry, my mistake.  The *horizontal* sync is nearly the same (~61kHz) for all three modes of interest (640x481, 640x482 and 640x483).  It is the *vertical* sync that is interesting.  

The 640x481 mode without "doublescan" or "vscan 2" works as expected at about 120 Hz.  

The 640x482 mode with the "doublescan" works as expected at about 60 Hz.  

The 640x483 mode with "vscan 2" wrongly works like the single scan mode instead of like the doublescan mode.  It has a vertical refresh rate of 120 Hz, where it should be 60 Hz.