[Bug 9714] Radeon driver doesn't produce stable image on external display

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https://bugs.freedesktop.org/show_bug.cgi?id=9714          
     




------- Additional Comments From wouter at telox.net  2007-01-20 14:35 -------
(In reply to comment #5)
> It is not surprising the reduced blanking modelines help, since vga outputs from
> notebooks are known to be generally not really good enough for clear output in
> high resolutions (though I don't know how well apple or specifically this
> notebook does). (And in fact the pixel clock is above the monitor's advertized
> maximum without it in 1920x1200).
> I'd have said it's just a not very high quality vga output, maybe coupled with a
> cable which degrades signal quality further, and the input circuitry in the
> monitor could make a difference too. However, if this works with OS/X, it
> apparently must be something else as timings used by OS/X are likely the same
> (though I'm not sure about sync polarity). 

I would have to concurr that the fact that it works flawlessly both using OS/X
and another (a bit older) powerbook rules out the fact that the hardware is
responsible. Furthermore, and I probably should have mentioned this before but I
forgot, the modeline that is included is pulled directly from the "additional
video modes" EDID information and has the correct (I checked the manual) sync
polarity. In addition, this exact modeline works for other people. 

> I'll wonder, is it possible that
> using "wrong" reference divider etc. degrades signal quality (as those are
> defaulted since obviously your chip doesn't have a pc bios)? Might be something
> else though.

When comparing the log with the other powerbook's log we find almost no
differences, one that comes to mind now is the following. In my log we find:

(II) RADEON(0): Probed PLL values: xtal: 27.000000 Mhz, sclk: 391.500000 Mhz, 
mclk: 202.500000 Mhz

while on the other one:

(II) RADEON(0): Probed PLL values: xtal: 27.000000 Mhz, sclk: 200.250000 Mhz,
mclk: 200.250000 Mhz

I don't know whether this is relevant. The different value in sclk probably
means my card is faster, however, the mclk value seems to differ more in my
case. Hope this helps.          
     
     
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