Re: parport - interrupt sharing possible?

Marcelo Tosatti
2004-07-12T19:08:18Z

On Sun, Jul 11, 2004 at 10:51:19PM -0500, Ryan Underwood wrote:
>
> Hi,
>
> Does anyone know if the generic parport interrupt handler is okay (or not)
> for sharing interrupts? The reason I ask is that I have a PCI parallel
> card with two ports on it. Without a IRQ sharing capability, it is not
> possible for both of them to operate in interrupt-driven mode. I tested
> a quick hack to enable IRQ sharing:
> http://home.icequake.net/~nemesis/parport.diff
>
> and it seems to work okay with both ports in use. I'm hoping someone
> more knowledgeable on the parallel port subject (Tim Waugh?) can shed
> some light on whether this is acceptable or not. The interrupt handler
> eventually ends up in parport_ieee1284_interrupt which really doesn't do
> much besides wake up sleepers.
>
> Thanks!
>
> PS: Heh, the power just went out and back on as I wrote this. Giving thanks
> for having multiple UPS units around!

Hi Ryan,

Quoting Tim Waugh:

> 2) Allows PCI parallel port to share an IRQ if possible. In limited testing
> this seems to be ok, but maybe the interrupt handler was not written for
> sharing. Someone else will need to ok this.

This seems dangerous to me. There are some issues with IRQs in
parport, although I think they are known and there is a fix around:
http://lists.infradead.org/pipermail/linux-parport/2004-March/000048.html

Incidentally, I have asked if there is anyone with more time than me
who would like to maintain the paride/parport bits, but no-one has
stepped forward. I see that Al Viro has fixed a lot of problems while
I've been busy with other things.