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

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Date:   Tue, 30 Aug 2016 21:21:12 +0200
From:   Peter Wu <peter@...ensteyn.nl>
To:     Ilia Mirkin <imirkin@...m.mit.edu>
Cc:     Roland Singer <roland.singer@...ertbit.com>,
        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>
Subject: Re: Kernel Freeze with American Megatrends BIOS

On Tue, Aug 30, 2016 at 02:13:46PM -0400, Ilia Mirkin wrote:
> 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'.

I doubt that the audio device is responsible here, that should only show
up after following very specific steps (runtime suspend/resume (PCI or
ACPI magic), remove PCI device, rescan bus).

> 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.)

I understood that Roland's intent is to check the power state, not use
the suspend functionality of bbswitch, if you load bbswitch without
module options amd do not write to /proc/bbswitch, then it allows you to
read out the actual status (you could also just use lspci -H1 for that
though).
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl