Re: x86_64, Haswell, unhandled vga irqs before i915 loaded

[Nikolai Zhubr]

Ping? Nobody interested? Maybe there is some more appropriate 
(specialized) place to ask?
Any hints appreciated,
Thank you.

Please CC me, I'm not subscribed.

Regards,
Nikolai

14.05.2016 11:21, I wrote:
> Hello all,
>
> Some of my motherboards exhibit the [in]famous bug of throwing unwanted
> (and unhandled) irqs from integrated intel video core on monitor cable
> plug/unplug events when there is no specific chipset driver loaded
> (yet). Searching some forums yields this apparently started happening
> (sometimes?) starting from Sandy Bridge, affecting both analog VGA
> output and digital (DVI, HDMI) outputs.
>
> Currently, I observe this with 4.1.13 kernel (I could also test some
> later one but I suppose nothing relevant has changed since).
> Unfortunately the warning message from the kernel in this particular
> case is extremally unhelpfull and confusing, because the irq line in
> question usually happen to be shared with some usb and/or netcard etc.,
> so kernel keeps talking about usb and/or netcard, so people end up being
> totally confused.
>
> How to reproduce:
> - get some relevant motherboard (Mine is gigabyte ga-b85-hd3 rev 2.1)
> - ensure i915.ko (or any fb drivers) not automatically loaded on boot.
> - watch dmesg and /proc/interupts
> - start plugging/unplugging VGA or HDMI monitor cable.
>
> What you will see then (approxmately):
>
> /proc/interupts:
> ...
> 16: 100001 0 0 IR-IO-APIC-fasteoi ehci_hcd:usb5
> ...
> (100000 counter increase in a fraction of second)
>
> dmesg:
> irq 16: nobody cared (try booting with the "irqpoll" option)
> ...
> Disabling IRQ #16
>
> Now meanwhile freebsd people have apparently managed to fix the problem
> with a one-liner patch, but I can not test it yet because adapting this
> patch for linux is a bit beyond my capability.
> This is the discussion:
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=156596
> This is the patch:
> https://svnweb.freebsd.org/base?view=revision&revision=284012
> This is the commit log:
> Disable VGA PCI interrupts until a chipset driver is loaded for VGA
> PCI devices. Else unhandled display adapter interrupts might freeze
> the CPU or consume a lot of CPU.
>
> My understanding is that the problem is caused by buggy BIOS rather than
> the kernel, but e.g. in my case no usefull BIOS update is available
> (yet?), and still I'd like to "fix" it anyhow.
>
> *** Please CC me, I'm not subscribed!
>
> Thank you,
>
> Regards,
> Nikolai