No VESA VBE DDC data on Linux / X / KDE boot --> bad DPI value --> font too big

[Alex Deucher]

On Mon, Dec 7, 2009 at 5:51 PM, Jeff B <JeffBatHome at myletters.us> wrote:
> Hi,
>
> I originally posted this in LinuxQuestions.org and got a response that I
> should post this here, so I am.  See my original post below or at
> http://www.linuxquestions.org/questions/slackware-14/no-vesa-vbe-ddc-data-on-linux-x-kde-boot-bad-dpi-value-font-too-big-771558/#post3769708
>
> I spent a fair amount of time poking around on the web looking for a
> solution to this.  There was a work-around, ie force X to use the right
> Dots Per Inch figure no matter what LIBVBE.SO says, but that's not a
> solution which can benefit anyone besides me.
>
> One thing I did note were MANY references to X not recognizing this or
> that device which also contained the error message "VESA VBE DDC Level
> none", and I have to wonder if they are having the same problem which is
> just showing up a different way.  At the time I write this Google gets
> "about 21,600" hits on "VESA VBE DDC Level none", so it may be a bigger
> problem than just what I am seeing.
>
>

If the vesa driver is not able to get an edid from the monitor it has
no way of knowing the size of the display so it defaults to 96 dpi.
So either your monitor has flakey ddc, or the vbe get edid call is
problematic on your card.  You may have better luck using a real
driver for your hardware rather than vesa.


> RSVP.  Thanks in advance.
>
> Jeff B.
>
>
> ============================================================
>
>
> Hi,
>
> I've been having a problem booting Linux (Slackware 12.2) / X / KDE on
> two of my machines. The SYMPTOM is that the fonts are too big once
> everything is up.
>
> More accurately, MOST of the time (NOT all of the time) when X / KDE
> starts after a Linux boot the characters on screen are too large. On the
> other hand, MOST of the time (but not all of the time) I can get the
> characters to be the right size by using Ctl-Alt-Backspace to restart X
> / KDE.
>
> Further, I see this problem on two different machines with two different
> motherboards, plus I did not have the problem until I installed
> Slackware 12.2, so I don't believe it's a hardware fault or a
> device-specific driver fault. Earlier versions of Slackware had run on
> both these machines for some time with no problem like this.
>
> I did some investigating and found differences in the Xorg.0.log files
> between the times when the characters are too big and when they come out
> to be the right size. The differences are summarized as follows:
>
>
>
> Xorg.0.log / Characters too big:
> --------------------------------
> . . .
> (II) VESA(0): VESA VBE DDC Level none
> (II) VESA(0): VESA VBE DDC transfer in appr. 0 sec.
> (II) VESA(0): VESA VBE DDC read failed
> [No VBE DDC info]
> . . .
> (--) VESA(0): Virtual size is 1024x768 (pitch 1024)
> . . .
> (==) VESA(0): DPI set to (96, 96)
>
>

not able to get an EDID from the monitor. driver defaults to 96 dpi.

>
> Xorg.0.log / Characters right size:
> -----------------------------------
> . . .
> (II) VESA(0): VESA VBE DDC Level 2
> (II) VESA(0): VESA VBE DDC transfer in appr. 1 sec.
> (II) VESA(0): VESA VBE DDC read successfully
> [Lots of VBE DDC info]
> . . .
> (II) VESA(0): My Monitor: Using maximum pixel clock of 140.00 MHz
> (--) VESA(0): Virtual size is 1024x768 (pitch 1024)
> . . .
> (**) VESA(0): Display dimensions: (390, 290) mm
> (**) VESA(0): DPI set to (66, 67)
>

Got an EDID from the monitor, set proper dpi.

>
>
> When KDE is given an incorrect (higher) pixel DPI (96,96) value, then it
> is going to use more X and Y pixels to form characters, and when those
> characters rendered on a screen with an actual DPI of (66,67) the
> characters will be too large.
>
> Obviously the problem is in obtaining the VESA VBE DDC data in the first
> place, leading to incorrect pixel DPI values. Fetching VESA VBE DDC data
> is done in /usr/lib/xorg/modules/libvbe.so, or at least that is where
> the VESA VBE DDC <whatever> messages exist.
>
> Versions:
>
> X.Org X Server 1.4.2
> Release Date: 11 June 2008
> X Protocol Version 11, Revision 0
> Build Operating System: Slackware 12.1 Slackware Linux Project
>
> Slackware: 12.2.0 patched up to date (Note xorg built for Slackware 12.1)
>
> Linux: 2.6.27.31-smp
>
> libvbe.so is in the Slackware package "xorg-server-1.4.2-i486-1"
>
> KDE version: 3.5.10
>
>
> This whole thing feels like a race condition in or around libvbe.so such
> that sometimes it works and sometimes it doesn't. Anyone know of a real
> fix for this, ie not a work-around forcing the DPI to the correct value
> in some X parameter file.?
>
> Thanks in advance.
>
>
> Jeff B.
>
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