Re: Linux 2.6.17: IRQ handler mismatch in serial code?

Mark Lord
2006-06-19T21:52:23Z

Alan Cox wrote:
> Ar Llu, 2006-06-19 am 15:45 -0400, ysgrifennodd Mark Lord:
>> If the drivers are written "correctly", they shouldn't grab the IRQ
>> until someone actually opens the device. Which means they should be
>> able the share the IRQ, so long as both devices are not in use (open)
>> at the same time.
>
> This is not the case for ISA bus. Most ISA hardware is physically unable
> to share and the drivers for such hardware intentionally grab the IRQ at
> load time to avoid it being mis-reused.

Eh? The vast majority of ISA bus devices have open-collector IRQ lines,
which means that two devices on the same IRQ are "wire-ORed" (but they really
use edges). There's no problem whatsoever with this in most setups.
I even implemented full support for it in the Linux IDE driver, way back when,
so that multiple cards could be installed on the same IRQ, and would work
just fine so long as access was serialized. This was the one of the original
motivations for the IDE "serialize=" parameter.

Cheers