Re: [gentoo-user] New machine: Contents of display are offset around 2 inches from the left hand side.

[Alan Mackenzie <acm@muc.de>]

Hello, Michael.

On Sat, Aug 24, 2024 at 20:36:11 +0000, Alan Mackenzie wrote:
> On Sat, Aug 24, 2024 at 16:40:38 +0100, Michael wrote:
> > On Saturday, 24 August 2024 14:25:31 BST Alan Mackenzie wrote:
> > > On Sat, Aug 24, 2024 at 10:44:44 +0100, Michael wrote:

[ .... ]

> > This reads like an unsuitable refresh rate problem.

> I've read the "information" section from my monitor's adjustment panel.
> It says 60 Hz. and 1920x1080 (on my current machine).  On the new
> machine, it reads 60 Hz., 2112x1016.  This looks like being at the core
> of the problem.  2112 / 1920 = 1.1 (more or less), i.e. 10% too many
> pixels.

> My monitor is ~52cm wide.  10% of this is the ~5cm. black strip at the
> LHS of the monitor.

> Is there any convenient way I can display the current EDID information
> block?

Yes, there is: there is the package x11-misc/read-edid, which contains
two utilities get-edid and parse-edid.  Calling # get-edid | parse-edid
produces, on my current machine:

This is read-edid version 3.0.2. Prepare for some fun.
Attempting to use i2c interface
No EDID on bus 0
No EDID on bus 2
No EDID on bus 3
No EDID on bus 4
No EDID on bus 5
No EDID on bus 6
No EDID on bus 7
1 potential busses found: 1
256-byte EDID successfully retrieved from i2c bus 1
Looks like i2c was successful. Have a good day.
Checksum Correct

Section "Monitor"
        Identifier "SMB2430L"
        ModelName "SMB2430L"
        VendorName "SAM"
        # Monitor Manufactured week 13 of 2011
        # EDID version 1.3
        # Digital Display
        DisplaySize 520 290
        Gamma 2.20
        Option "DPMS" "true"
        Horizsync 30-81
        VertRefresh 56-75
        # Maximum pixel clock is 170MHz
        #Not giving standard mode: 1280x800, 60Hz
        #Not giving standard mode: 1280x960, 60Hz
        #Not giving standard mode: 1280x1024, 60Hz
        #Not giving standard mode: 1440x900, 60Hz
        #Not giving standard mode: 1600x1200, 60Hz
        #Not giving standard mode: 1680x1050, 60Hz
        #Not giving standard mode: 1152x864, 75Hz
        #Not giving standard mode: 1440x900, 75Hz

        #Extension block found. Parsing...
        Modeline        "Mode 0" +hsync +vsync
        Modeline        "Mode 1" +hsync +vsync
        Modeline        "Mode 2" +hsync +vsync
        Modeline        "Mode 3" +hsync +vsync
        Modeline        "Mode 4" -hsync -vsync
EndSection

..  On my new machine, it is almost identical, just using I2C bus 0,
rather than 1.

It is now clear that EDID contains not an optimal screen setting, but
instead ranges (for example 56-75 Hz. screen refresh rate).  The
question arises, what exactly puts the display into 1920x1080 60Hz. at
boot up time?  Something must be chosing that resolution.  I've tried
grepping the kernel sources, but there are a lot lf "1920x1080"s there.
:-(

[ .... ]

> My hypothesis at the moment is that something in the new machine is
> wrongly pumping out 2112x1016 in place of 1980x1080 and this is
> diminishing the size of (and reducing the quality of) the displayed
> image.

> I think the EDID being received from the monitor and KVM-box are correct,
> but that the BIOS is applying some "correction" to them, for some reason.
> Maybe I should try resetting the CMOS ram.

> > Let's hope one of these things delivers a working display for you.  :-)

> Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).