Xrandr only detects one card: 2 x GTX480, triple-head (Linux Mint 16)

Hi all,

I will attempt to post an nvidia-bug-report.log.gz later (I’ve had to revert to nouveau) but here’s the problem:

I am running Linux Mint 16 (Petra)
I am running the default driver nvidia-319 shipped with the distro
I have 2x GTX480 cards
I have three monitors

Using the Nvidia driver, all monitors and GPUs are picked up by the proprietary utility.

However, similarly to the report at https://devtalk.nvidia.com/default/topic/719768/linux/304-121-ubuntu-14-04-xrandr-1-4-multi-gpu-not-being-detected/ when I run xrandr --listproviders I am only shown a single provider – the first card.

I do not want to run xinerama as it is a pain in the neck to setup and should be superseded by xrandr.

Using the nouveau driver I can use all three screens exactly as I would like, but the performance is not good.

So, I have two questions:

1.) Is this behaviour by design or a bug? I note at http://uk.download.nvidia.com/XFree86/Linux-x86/319.12/README/randr14.html that the driver only supports the Source Output capability; would that stop me just seeing two different card providers in xrandr?

2.) If the former is true, is there a way that I can work around this? Could, for instance, setting the modesetting driver on one of the devices be a workaround?

Any suggestions would be very much appreciated.

Best wishes,

Martin

nvidia-bug-report.log.gz (126 KB)

To help anyone else who stumbles across this post, I’ve blogged about my solution at: https://www.martineve.com/2014/04/15/enabling-a-triple-head-3-monitor-setup-on-linux-mint-16-petra-with-two-nvidia-cards/

The key aspects to note was that I had to install the SLI hardware bridge and use SLIMosaic and BaseMosaic modes in the end.

It turns out that xrandr only recognises one provider at the end anyway, but I do now have a triple-head dual-GPU setup with xrandr 1.4 working.

The only final bug I found was that, using 331.20 I encountered:

[ 209.366] (EE) NVIDIA(GPU-0): Failed to find a valid Base Mosaic configuration.
[ 209.366] (EE) NVIDIA(GPU-0): Invalid Base Mosaic configuration 1 of 1:
[ 209.366] (EE) NVIDIA(GPU-0): GPUs:
[ 209.366] (EE) NVIDIA(GPU-0): 1) NVIDIA GPU at PCI:1:0:0
[ 209.366] (EE) NVIDIA(GPU-0): 2) NVIDIA GPU at PCI:2:0:0
[ 209.366] (EE) NVIDIA(GPU-0): Errors:
[ 209.366] (EE) NVIDIA(GPU-0): - The video link was not detected
[ 209.366] (EE) NVIDIA(GPU-0): - Trouble accessing PCI Config Space

This now works in 319.60 though.

I think the confusion here is that, at least for now, RandR providers are X screens, not GPUs. So it’s expected that if you only have one screen, there is only one provider.

Do you still have the bridge-detection problem in 337.12?

Hi aplattner,

Thanks for the response – and the clarification on RandR (sorry for getting that wrong).

I have just installed 337.12 and am pleased to report that the bridge detection problem is gone!

Best wishes,

Martin