RE: RE: RE: 1 IRQ line for all bridged dev? RE: prob w/PCI add-in cards w/PCI 2PCI bridge

[Lame Brooks-G14738 <Brooks_Lame@mcg.mot.com>]

	First, it is interesting to note that PCI Interrupt Pins (PCI 2.1
sec 2.2.6) are optional, thus hinting at the forthcoming message based
interrupt spec in PCI 2.2 (sec 6.8 Message Signaled Interrupts).

> Near all mainboards do Interupt routing the right way, this means
> PCI-Interupts are routed (INTA-D), but the INTB of slot 1 for 
> example, is
> hardwired to INTA of slot 2 (or vice-versa) .

	Note: that is not defined as the "right way" in the PCI spec.
According to the PCI spec, interrupt routing on the motherboard is system
specific and may be done just about any way the designer pleases, so long as
all of them are connected to an input on the interrupt controller (and they
meet the signalling requirements, and the associated PCI BIOS functions
work, etc).

> So if you use 
> INTB, you must
> be aware that your Interupt could (or may) be shared with 
> other PCI-Cards.
> At this time, there are many cards (and drivers), that are 
> not able to share
> Interupts. 

	Specifically, see PCI 2.1 sec 2.2.6, paragraph 3: "...the device
driver may not make any assumptions about interrupt sharing.  All PCI device
drivers must be able to share an interrupt (chaining) with any other logical
device [PCI] ..."  
	So, if you run accross a released PCI add-in card product that can
not share interrupts, call the manufacturer, or beat them with a stick,
until they understand that their product does not work correctly, that they
are creating problems for system integrators, and that their product needs
to be fixed.  When proprietary, incompatible, non-conforming products are
allowed to enter the market under the banner of PCI, they contribute to a
breakdown of the spec and result in compatibility problems for users.
-- BrooksL

..snip..