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wikavalier

Member

Registered: 2013-01-22

Posts: 27

video switch for a headless root system?

Weird title huh?

I am building a base OS to deploy kvm-vfio, lxc and docker/rocket systems. Since those systems will have direct access to the hardware to play video i dont really need to have X working in the "base OS", which is quite convenient as X is my nemesis. But, i do want to use only one monitor (with one cable).

Long ago I found (I swear!) a post explaining how to use one of the ttys (ruled by igp) to output whatever the discrete videocard was playing. Right now i am able to see a "ghost" monitor in my windows guest, which i assume is the FDI (flexible display interface), and i want to tell the intelHD that signal shall be printed in the monitor. I think it was using randr and it was quite straight forward, but i cant find it anymore.

I tried to follow the wiki links for the alex williamson's switcheroo, all the hybrid X video switches (bumblebee/prime) but i am now clueless as they rely on X and are way too complex for what i want to do.

Do any charitable soul have any clue to point me in the right direction?

Thanks in advance

alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

Re: video switch for a headless root system?

Long ago I found (I swear!) a post explaining how to use one of the ttys (ruled by igp) to output whatever the discrete videocard was playing.

Either you misunderstood that post or I'm misunderstanding yours. It sounds like your scenario involves the discrete card not connected to a monitor, its output instead rerouted to the integrated video port. Is that correct?

---

But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner

wikavalier

Member

Registered: 2013-01-22

Posts: 27

Re: video switch for a headless root system?

It sounds like your scenario involves the discrete card not connected to a monitor, its output instead rerouted to the integrated video port. Is that correct?

Exactly!

That is why i am asking for help. I do remember (doesnt mean that is real, though) that there was a way to tell the IntelHD to output the ghost monitor (as seen by the nvidia in windows) to display that video in a tty. I think it involves the use of the xrardr (but that wasnt related to x...).

Reading thoroughly the vgaswitcheroo, i think this is the only way to go. But i dont have the damn /sys/kernel/debug/vgaswitcheroo in place.

Regards!

alphaniner

Member

From: Ancapistan

Registered: 2010-07-12

Posts: 2,810

Re: video switch for a headless root system?

I seem to remember reading wistful talk on the vfio ml about merely scraping a single frame from the buffer of the discrete card and dumping the raw data to a file. So I kind of doubt rerouting discrete to integrated in real time is something that has ever been done.

I'm also doubtful that vga_switcheroo is applicable here. Doesn't it involve one GPU being turned off? Also, it and other hybrid schemes involve special hardware AFAIK. What is your system?

---

But whether the Constitution really be one thing, or another, this much is certain - that it has either authorized such a government as we have had, or has been powerless to prevent it. In either case, it is unfit to exist.
-Lysander Spooner

wikavalier

Member

Registered: 2013-01-22

Posts: 27

Re: video switch for a headless root system?

Thanks for the patience,

It is possible, i was able to do that in windows running locally. It seamlessly operates the FDI, so you can connect one DVI to the mobo and other one to the discrete card and move the videogame instance between them.My system is an i7 (4770) and a geforce 870ti.

As far as i understand from the vga-switchero, it implies to shutdown the discrete but also to output the video using the selected video card. So i assumed that the use case is a laptop, where you have only one screen, and i guess one "cable". But i cant barely follow the documentation.

Regards

EDIT.
It seems that i have misinterpreted the post. I am going to try the byo vga switcheroo.

Last edited by wikavalier (2015-10-16 20:28:03)

wikavalier

Member

Registered: 2013-01-22

Posts: 27

Re: video switch for a headless root system?

After keep researching for a while, i realized that intel's FDI is in charge of using the integrated video card (intelHD) as a PCI/regular video card. Not controlling an internal video switch.

Windows is using a third party software that performs like PRIME/bumblebee. And both, through software, creates an hybrid X environment that can be "painted" using one or the two videocards at the same time. Sadly, for linux, is implemented only in laptops as those systems relies on the ACPI.

byo/ switcheroo is also doing something like above but in a lower level (i think it is part of them) and it also is meant for laptops.

So, in your desktop, if you VFIO'ed the external video card, it will need its own cable to be connected to the monitor. There is no way right now to "internally" reroute the external videocard to the integrated videocard.

That is a pity as i will need another 5m HDMI cable to connect the computer to the TV. Or an HDMI switch and 2 more 1m HDMI cables.

Thanks for the gideance alphaniner.

Regards,

W