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System generate IRQ's by itself ?
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Myu
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PostPosted: Thu Feb 04, 2016 6:22 pm    Post subject: System generate IRQ's by itself ? Reply with quote

Hello Gentooers,

I've a rather small and not really pressing issue but I would like to get to the bottom of it if I can. It might be related to my hardware or to an ( hopefully ) good surnatural spirit :)

My system is generating IRQ by itself ... (even without any HID devices like mouse or keyboard plugged )

I can see it in multiples ways :

If I'm on a terminal in the middle of an output, it scrolls down often after a few seconds ( 5 to 20 )

If there's xscreensaver active, I often get the username / password prompt for no reasons

If I'm watching a fullscreen video on youtube for instance, the controls are reapparing from time to time.

Could there be a way to watch an output of HID IRQ's ? Or all IRQ's even ?

Have a nice evening !
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NeddySeagoon
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PostPosted: Thu Feb 04, 2016 8:36 pm    Post subject: Reply with quote

Myu,

This is possibly the result of having PS/2 mouse and keyboard support enabled but no devices connected.
PS/2 is actually a simplified serial port. With no devices connected, the wires act like antenna and pick up electrical noise.
Every now and again, this electrical noise generates a valid character and a IRQ is raised.

I have not seen it a lot.

USB data is organised into packets. Its much harder to generate a random but valid USB packet, so it tends not to happen with USB.
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Myu
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PostPosted: Thu Feb 04, 2016 8:54 pm    Post subject: Reply with quote

Hi NeddySeagoon,

This is an interesting (and unexpected) thought to say the least !

Indeed I do have a PS/2 port and support enabled in my current kernel. I'll see if disabling them does any good.

Thank you for your kind answer, I'll keep you posted :)
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NeddySeagoon
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PostPosted: Thu Feb 04, 2016 8:58 pm    Post subject: Reply with quote

Myu,

Another possible fix is to make fake PS/2 devices that do nothing more than connect the data line to 0v.
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Myu
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PostPosted: Thu Feb 04, 2016 9:12 pm    Post subject: Reply with quote

Neddy,

So with PS/2 disabled on the BIOS and PS/2 support removed from the kernel, it still happens quite often.

Your second idea is interesting as well, although I wonder if it would have any impact on a BIOS-disabled PS/2 port.

I'll see if I can tinker with a PS2 to usb adapter to make something like you've proposed.
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NeddySeagoon
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PostPosted: Thu Feb 04, 2016 9:18 pm    Post subject: Reply with quote

Myu,

Look in /proc/interrupts

Code:
           CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       
  0:         64         36         87        517      10282     748776   IO-APIC   2-edge      timer
  1:          0          0          0          0          0          2   IO-APIC   1-edge      i8042

IRQ 1 is the i8042 PS/2 controller.
I have a total of 2 i8042 IRQs in a few hours. I do not have any PS/2 devices connected.
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NeddySeagoon

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Myu
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PostPosted: Thu Feb 04, 2016 9:27 pm    Post subject: Reply with quote

Neddy,

I see ! So it's almost quite common.

On my end, I do not have a i8042 IRQ (after the changes of course) :

Code:
 0:        122          0          0          0   IO-APIC-edge      timer
  8:         21          0          0          0   IO-APIC-edge      rtc0
  9:          0          0          0          0   IO-APIC-fasteoi   acpi
 16:     110667          0          0          0   IO-APIC  16-fasteoi   ehci_hcd:usb1
...

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NeddySeagoon
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PostPosted: Thu Feb 04, 2016 9:36 pm    Post subject: Reply with quote

Myu,

Well, if you no longer have a i8042 entry, its not PS/2 related.
You don't have IRQ3 and 4 either, which are the real serial ports fitted to older PCs.
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NeddySeagoon

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