[LinuxBIOS] HT interrupts

Segher Boessenkool segher at kernel.crashing.org
Thu Feb 15 16:07:05 CET 2007

> Sorry to spam again but I couldn't figure out this on my own.  
> Questions:

You again replied to an unrelated message instead of starting
a new thread too, sigh.

> 1. Does LinuxBIOS actually program the HT interrupt definition 
> registers
> based on the interrupt capability and mobo config, or does Linux do 
> this? Or
> is it up to the driver?

LinuxBIOS has to do at least some of the configuration.  It
probably does it all, I didn't check.  Linux will at runtime
change some settings.  Unrelated device drivers do not touch
any of this.

> 2. What's the recommended way of doing HT interrupt that will work 
> with both
> APIC and 8259?  EOI seems to be APIC only (can be turned off in the
> interrupt request) and I guess I can't rely on EOI to always be there?

I have no idea what your question is.  You *have* to do EOI
on level triggered interrupts and you *have* to refrain from
using it on edge triggered interrupts, or things will go
(horribly and/or subtly) wrong.

> 3. EOI in a way acts as flow control.  So without EOI is it possible 
> that I
> can flood the PIC/APIC with too many interrupt packets?

No, only one interrupt packet is sent from the HT APIC over
the HT bus; and only one packet (the EOI packet) is sent

> I suppose the
> credit based flow control in HT can take care of this...

That doesn't prevent flooding, it just prevents losing


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