Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

[Anthony Liguori <anthony@codemonkey.ws>]

On 09/04/2011 08:36 AM, Jan Kiszka wrote:
> On 2011-09-04 15:32, Anthony Liguori wrote:
>> I prefer to not think of IRQs as special things.  They're just single
>> bits of information that flow through the device model.  Having a higher
>> level representation that understands something like paths seems wrong
>> to me.
>>
>> I'd prefer to treat things like device assignment as a hack.  You just
>> need code that can walk the device tree to figure out the path (which is
>> not generic code, it's very machine specific).  Then you tell the kernel
>> the resolution of the path and are otherwise completely oblivious in
>> userspace.
>
> See it as you like, but we need the support, not only for device
> assigment. And I do not see any gain it hacking this instead of
> designing it.

You can design a hack but it's still a hack.

Device state belongs in devices.  Trying to extract device state 
(interrupt routing paths) and externalizing it is by definition a hack.

Having some sort of global interrupt routing table is just going to add 
a layer of complexity for very little obvious gain.

The PCI bus *is* the I/O APIC for all intents and purposes.  Being able 
to ask the i440fx for the interrupt corresponding to a device is a very 
simple task that involves no generic code.  That's more than enough to 
support device assignment.

Why overcomplicate things when the problem can be solved robustly with 
most likely a 10 line function?

Regards,

Anthony Liguori

>
> Jan
>