Consider implementing dGPU mux switching

[ilikenwf]

Dasharo recently added the support for it; I know that the bonw15 supports it and very likely many others...

@crawfxrd doing this would allow force enabling g-sync on supported models in the nvidia settings in Linux. Under Windows, it's well...Windows so idk there...

Dasharo/dasharo-issues#1024 (comment)

Implemented in:

Dasharo/coreboot#632
Dasharo/edk2#229
Dasharo/ec#68

[RileyMathews]

Does the bonw15 actually have a mux? I'm curious how you have confirmed this. I just stumbled across this issue when coming here to report another firmware issue but I thought I saw on some other issue in system76 (I think system76-power repo?) where someone from S76 said that none of their models since like 2022 has had a mux switch?

I've been having lots of issues getting some wayland compositors to run on dual GPU on my bonw15 but if I could mux switch the nvidia card to drive the internal display and external displays I think that would help a ton.

[ilikenwf]

Does the bonw15 actually have a mux? I'm curious how you have confirmed this. I just stumbled across this issue when coming here to report another firmware issue but I thought I saw on some other issue in system76 (I think system76-power repo?) where someone from S76 said that none of their models since like 2022 has had a mux switch?

100% yes - I pulled the appropriate pin high by force in the EC and got an nvidia only mux, and in nvidia dgpu mode on top of that managed to enable forced g-sync under linux. Windows would not cooperate...and I had not brightness control so my eyes were fried.

I have the schematics for the x370SNW which is the platform bonw15 is based on...so yes, it has a mux, and anything with a dgpu likely does too.

Scroll to the bottom of the page here for those pdfs: https://download.schenker-tech.de/package/schenker-key-17-pro-e23-e24-ske17pe23-ske17pe24/

I need to push my adjusted EC code sometime, I guess, but it's not a complete implementation with a toggle setup yet or bios integration.

To successfully finish mux switching/choosing we'll need to probably replace the LCD FN hotkey combo to toggle the mux, or, more ideally, with the gpio exposed in the EC code, add a menu option to the bios that lets us both choose the mux, as well as the primary GPU or dGPU or just one of them to use. I believe that some Dasharo machines already have this feature now - amongst others I wish that System76 would backport to their own firmware.

[RileyMathews]

Oh that's awesome to know! Forgive some ignorant questions here but I'm super curious how to do this on my laptop as well...

By 'pulled the appropriate pin high by force in the EC' do you mean you opened up the laptop and manually flipped a switch? Or is this referring to something you are doing in code to toggle something in bios? I spent a lot of time a few months ago searching around for more information on how to flip a mux switch but the most I could come up with is basically "sorry if your bios doesn't support it your out of luck" and then when I stumbled across the S76 employee implying my model didn't have it I just kind of gave up and resigned myself to running i3/Xorg until this machine dies 🙃.

Any info you can provide for me to do this on my system would be amazing! I am running arch on my system if that changes anything.

[ilikenwf]

A GPIO is basically an on/off switch. They're used all over the place on modern computing devices, at various levels. So yes, I'm more or less force enabling the mux. The downside of doing it that hacky way is that you'll have a black screen until the OS boots up. What I did was dangerous and for the sake of testing, and because there's not an easy mechanism baked into the EC and bios to toggle things the way we want to set them up, it's not really safe to do using my current code.

If your bios doesn't support it, you are indeed out of luck, but our bios is open source, and our EC is open source too...so it can be done, it just hasn't been (fully) on our machines yet, so they weren't really lying, per se it's just not implemented officially.

I also run arch, but this is something that I'd suggest, until you're at the least somewhat familiar with building and modifying the bios and EC, you steer clear of unless/until we get an official implementation or I find the time to fork and pull request what's needed to do it - because in your case, if something goes wrong, you probably don't have the equipment needed to manually recover from a bad EC or bios flash (though that can be had).

If you're technically minded and can learn the languages involved, though, and get familiar with the EC and coreboot code, we could both throw in on this as time permits us too. Personally, I'd really love to see the devs here, who are brilliant, consider copying most of the good features from Dasharo, whose work for the Clevo based machines is originally forked from System76 anyway...the intel ME state toggle options, bios password, mux switching, other security and configurables...it would be an undertaking but would really make the security minded folks even more keen of System76 compared to just attracting open source enthusiasts like us.

[RileyMathews]

Hmm I see. Yeah I'm not sure I'm in the best place to tinker with this right now then 😬. I would consider myself pretty technically competent but I have no experience getting that low level in the tech stack. The most I've done in that realm is just updating my BIOS using official tools. And also seeing as how my S76 is my work laptop... yeah not going to do any high risk maneuvers on it. If this was my personal laptop though I would totally be going down this path 😆.

Let me know if there is anything else I can do to help out here! I'll also give @crawfxrd a tag to say there is at least one other user who would absolutely love this functionality in the BIOS!

[crawfxrd]

It's MUX_CTRL_BIOS in the EC code. It's not hooked up to anything so the default (GPIO port data low) always sets eDP to iGPU control.

Models with this pin are:

• addw2
• addw3
• addw4
• bonw15
• gaze17-3060
• oryp11
• oryp12
• oryp7
• oryp8
• oryp9
• serw13

Previous question on mux control: system76/ec#350
And their attempt to add it: system76/ec#351

[RileyMathews]

Just to give a little more context as to the 'why' of wanting this feature for me at least. I prefer running minimal window managers like i3. I have started looking into wayland options since that seems to be where the winds are blowing linux towards. However on my bonw15 with dual graphics right now my only option for wayland compositors like sway and hyprland is to run dual GPU since (without the mux) only the intel graphics can drive the internal display and only the nvidia card can drive an external display. In this configuration with choosing either card as the primary renderer and having it offload the other monitor to the connected card leads to a very high load on the hardware. When monitoring in some cases I can drive a single core on my CPU to constant 80-90% by just watching a youtube video.

I have pretty much confirmed that either card can handle wayland fine alone. Either by not having an external monitor connected or explicitly telling wayland through config vars to not use the intel card at all (which consequently means the laptop display is shut off during those graphical sessions) in this state either card hums along just fine which leads me to believe that if I could flip the mux switch and run the internal AND external displays solely on the nvidia GPU that it would also run just fine. But this is definitely just an assumption on my part.

[RileyMathews]

@crawfxrd thanks for the clarification on the mux switching models! Is there any chance that anyone from S76 would be picking this up anytime soon or would this have to be an outside contribution?

After looking into what it takes to reflash a broken bios I think I might be up for getting the stuff needed to flash from a spare raspberry pi I have lying around and venturing down this path to see what happens.