Re: [PATCH kvm-unit-tests 2/4] Introduce a C++ wrapper for the kvm APIs

Gleb Natapov
2010-11-25T08:35:47Z

On Wed, Nov 24, 2010 at 12:53:00PM -0600, Anthony Liguori wrote:
> On 11/24/2010 12:34 PM, Gleb Natapov wrote:
> >>>>Right, and real HW does composition in the PIIX3 device. So let's
> >>>>not regret making everything an ISA device later.
> >>>>
> >>>You design by packaging not functionality?
> >>No, if you want the ability to remove devices from the PIIX3, fine,
> >>but don't call them ISA devices just for the sake of it.
> >PIIX3 may be totally implemented in FPGA code. I do not care. This is
> >implementation detail. What important is that it provide the same
> >functionality as ISA devices in the first IBM PC. That is why they are
> >ISA devices and should be modeled as such. Otherwise you will have to
> >redesign everything when you'll want to move to another chipset
> >emulation that uses new and improved SuperIO-2XT technology inside.
>
> The ISA slots (technically XT) were basically daughter board
> connectors. They routed pins from a bunch of devices on the
> motherboard to external daughterboards.
>
> This included the *unused* IRQ pins, the left over DMA channels,
> etc. Everything else was hard wired.
>
> The XT connector only exposes pins 3, 4, 5, 6, and 7. The ISA
> connector then added IRQs 10, 11, 12, 14, and 15.
>
> So if a device uses IRQ 0, 1, 2, 8, 9, or 13, it's by definition not
> an ISA device. It was hard wired on the motherboard.
>
I don't understand why do you claim that device that is hard wired on
the motherboard is not ISA device. We have many PCI devices internally
in modern chipsets. They are as PCI devices as add on PCI cards.

--
Gleb.