parport - interrupt sharing possible?

parport - interrupt sharing possible?

[Ryan Underwood]

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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!

-- 
Ryan Underwood, <nemesis@icequake.net>

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Re: parport - interrupt sharing possible?

[Marcelo Tosatti]

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.