linux-kernel - Re: Kernel Freeze with American Megatrends BIOS

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Date:   Tue, 30 Aug 2016 14:13:46 -0400
From:   Ilia Mirkin <imirkin@...m.mit.edu>
To:     Roland Singer <roland.singer@...ertbit.com>
Cc:     Emil Velikov <emil.l.velikov@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        Peter Wu <peter@...ensteyn.nl>
Subject: Re: Kernel Freeze with American Megatrends BIOS

On Tue, Aug 30, 2016 at 2:02 PM, Roland Singer
<roland.singer@...ertbit.com> wrote:
> I configured bbswitch to not set any states automatically...
> So it's possible to obtain and verify the GPU power state.
>
> However I removed the bbswitch module and booted with nouveau.
>
> Kernel 4.7.2: nouveau switches the discrete GPU off.
>               I can't trigger the freeze, because bbswitch is missing.
>               I'll work with the system and see if it will freeze.
>
> Kernel 4.8-rc4: nouveau does not care about the power state and
>                 the discrete GPU is never switched off. I will notice
>                 this, because the second cooling FAN will stop...
>                 Same log messages as send before.

That's surprising. I believe there's an issue with the new logic when
there's an HDMI audio subdevice. However that only appears if there's
a cable plugged in, at least in the systems Peter tested. You should
be able to see whether it's there or not with 'lspci'.

You can check for sure by looking in the vgaswitcheroo state. It
should say DynOff when it's powered off.

Either way, I think using bbswitch + nouveau isn't supported by
anyone, so if you want to use it that way, you're on your own. (You
may want to load nouveau with runpm=0 so that nouveau doesn't try to
manage the GPU suspend stuff.)

  -ilia