How to force X to use a specific GPU / output

[Polytropon]

On Wed, 4 Dec 2019 13:28:18 -0600, CyberLeo Kitsana wrote:
> On 11/30/19 2:02 PM, Polytropon wrote:
> > With a HP Pavilion dm-1 "netbook" laptop I got, I have a problem
> > since I connected a HDMI display: There are now several green
> > pixels on the screen, in areas where the color is nearly black.
> > They also appear in videos and make the "compression squares"
> > visible.
> > 
> > Note: Those are _not_ defective pixels on the display.
> > 
> > When the system boots up, everything is fine. As soon as the
> > system enters X, color isn't displayed properly as before.
> > The video output on both HDMI and VGA, even at the same time,
> > shows the colors correctly.
> > 
> > During searches related to that problem, I once found an image
> > that looked like what I'm seeing, and I read an article, even
> > though regarding a Macbook, that this problem occurs due to
> > internal switching between graphics hardware depending on if
> > the internal screen should be driven or an external one. Sadly,
> > I cannot find any of those again...
> > 
> > However, I found this:
> > 
> > http://cdn.avsforum.com/3/3e/3e8d725c_vbattach231475.png
> > 
> > You can see "green clouds" around the curves, and the colors
> > look slightly distorted. Everything that is "nearly black" now
> > looks green - the _same_ green. The image above shows that
> > problem on something that looks like "Windows 7".
> 
> <snip>
> 
> This looks very much like what happened to several of my old Gateway 
> desktop LCDs when their internal LVDS connector became loose and started 
> slipping off the back of the display panel assembly. Who holds a 
> high-speed data connector in place with masking tape, anyways?

But attaching a HDMI cable doesn't cause tape or glue to move.
I can hardly imagine a mechanical defect in this case, as moving
the lid doesn't cause a kind of effect like "picture changes
when flex connector is moved" - this is _not_ the case here.

I really suspect some "firmware hickup" inside the graphics
part of the machine.

What I tried:

Switching the connectors (LVDS, HDMI, VGA) works, but has no
effect. It doesn't matter if all of them are in use at the
same time, or none, or only one.

Resetting the BIOS settings and "hard resetting" the laptop
(the procedure where you disconnect all power and batteries
and hold the power button to drain any remaining energy) also
does not work.

Is there something else that can be seen as "totally reverting
to factory settings"? I read a lot about reinstalling "Windows"
and drivers and whatnot, but that clearly doesn't apply here,
as it only deals with common "Windows" driver problems.



> > What worries me most:
> > 
> > The display was _fine_ before connecting a HDMI TV as external monitor!
> 
> This may be a coincidence.
> 
> If you can (and are willing to) disassemble the netbook, double-check 
> that the LCD cable is securely connected at both ends, that the 
> connectors are free of corrosion, and that the cable is not being frayed 
> or damaged by hinge movement.

I doubt that will help, for the following reasons:

When the laptop is in BIOS text mode and FreeBSD console "text
mode" (which already is a graphics mode), absolutely no problems
can be caused, not even by hinge movement. However, now as I know
how to open the laptop (idiotic plastic "noses" holding the main
cover, plus screws hidden beneath rubber pads which already have
fallen off), I could at least have a look at it. But shouldn't
the problem of a damaged connection be visible in _any_ mode where
the display has non-black content?

Additionally, look at the image again: That doesn't really _look_
like a typical "flex damaged" problem - those look different. The
little green dots that appear everywhere where the color is "not
grey anymore, but not black already", i. e., in places with a
very low but nonzero RGB value (if I may simplify it like that),
and that _some_ of them are flickering at a high frequency, while
others are constant, and they are all the same (!) kind of green,
well, that seems to point into a different direction. I'm saying
this from my limited experience repairing things like portable
DVD players, camcorders, and laptops.

But who knows - that's all very complicated technology no longer
meant to be understood by people. :-)





-- 
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...