xf86-video-intel - enforce a given resolution on the DVI port? [success!]

Dag Bakke dag at bakke.com
Mon Feb 5 10:08:23 PST 2007

On 02/05/2007 06:07 PM, Barry Scott wrote:
> Keith Packard wrote:
>> You'll need to construct a modeline on your own then, and then link it
>> to the DVI output with another monitor section linked to the DVI-1
>> output (mode line below computed with the 'cvt' program):
>> Section "Monitor"
>>     Identifier    "TV"
>>     ModeLine    "1366x768" 85.25  1368 1440 1576 1784  768 771 781 798 
>> -hsync
>> +vsync
> Did you mean to use 1368 for the h usable size?
> Can the intel chips be programmed with 1366 to match the panel? or do 
> they have a x8
> restriction like the EDID spec?

Looks like a limitation with cvt, the tool used to generate the modeline.

My current modeline looks like this:
Modeline "1366x768R"   72.25  1366 1416 1448 1528  768 771 781 790 
+hsync -vsync

cvt put '1368' after 72.25, I just modified it manually. The TV accepts 
either one. (X reports 1368x768 or 1366x768)

And so I have the resolution I want:

mediapc at mediapc ~ $ xdpyinfo | grep dimen
   dimensions:    1366x768 pixels (542x406 millimeters)

And all is well. Almost. Note the dimensions? As the GUI of the 
application I use isn't made for 16:9 *and* appears to care for dpi, the 
error makes it stretched out over the entire screen. A useful sideeffect.

Still, Xorg.0.log states:

(II) intel(0): Max H-Image Size [cm]: horiz.: 71  vert.: 40
but later:
(==) intel(0): DPI set to (75, 75)

If I enforce the dpi with
DisplaySize       701 396
in the relevant "Monitor" section, X comes up with :

   dimensions:    1366x768 pixels (713x401 millimeters)
   resolution:    49x49 dots per inch

which may be closer to the truth in my case. Now, *I* assume square 
pixels on my TV, but who told X to do so? :-) EDID data perhaps?

So one could say that there are possibly two bugs lurking here:
1. the dpi appears hardcoded. X does certainly not make use of probed 
2. if a corrected DisplaySize is provided by the user, X fixes it up so 
it matches the given resolution with square pixels.

If either of these are considered bugs, I'll be happy to stuff them into 
bugzilla. Let me know.

I have attached my current xorg.conf and the resulting Xorg.0.log for 
the benefit of those struggling with the same problem. Google tells me I 
am not alone...

Keith: thanks!

Dag B
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