Subject: Re: qtopia
To: Steven M. Bellovin <>
From: Garrett D'Amore <>
List: tech-kern
Date: 06/03/2006 21:33:03
Steven M. Bellovin wrote:
> On Sat, 3 Jun 2006 19:35:02 -0400, Michael Lorenz <>
> wrote:
>>>>> Except that some of us can't look at CRT displays with refresh rates
>>>>> below 85Hz without seeing 'large area flicker' - which hurts.
>>>> Then you should switch resolution as well.
>>>> On a TFT that doesn't make much sense though and I think we should 
>>>> have reasonable support for both cases.
>>> Well, if the monitor supports certain modes with >=85Hz vertrefresh, 
>>> the display driver should as well (if the RAMDAC supports it, that 
>>> is). On a sidenote, I have my two IIyama VMP454s running at 
>>> 1600x1200x32 @ 100Hz without problem. As for TFTs, I was under the 
>>> impression that the analog refresh rate doesn't matter because the 
>>> internal analog->digital panel converter has no glow decay like a CRT 
>>> (same goes for the refresh rate of a panel connected via DVI btw).
>> The point was that it doesn't make sense to switch /resolution/ on a 
>> TFT 
> Actually, sometimes that is sane.  More precisely, on laptops with
> external VGA connectors, you sometimes need to switch resolutions -- on
> both the internal and external ports -- so that you can display on both
> simultaneously.  I did that just yesterday (using xrandr) when giving a
> talk -- my laptop is 1400x1050, but the projector preferred 1024x768.  It
> looked *ugly* on my screen, but I could read it, as could the audience via
> the projected image.
> 		--Steven M. Bellovin,

FYI, my EDID support in radeonfb would "pick" the greatest common
denomination in this case.  Which probably means it would settle on
1024x768 (XGA), depending on what the projector claims to support in its

Of course, this all breaks down horribly with monitors that lie or give
bad information in their EDID.  Hopefully there aren't too many of those
out there.  So far, I've not run into any, but my sample set is pretty

One interesting note: a KDS monitor (CRT) made in 2000 apparently does
not support EDID via DDC2.  I've not tested DDC1, as I don't have the
code written to use DDC1.  I wonder how many people out there have 6
year old monitors like this that are going to have trouble with no DDC2.

Garrett D'Amore, Principal Software Engineer
Tadpole Computer / Computing Technologies Division,
General Dynamics C4 Systems
Phone: 951 325-2134  Fax: 951 325-2191