Re: PCI irq sharing and X on Linux

Wakko Warner (wakko@animx.eu.org)
Wed, 7 Jul 1999 20:09:49 -0400

> > Because of a bunch of reasons (find the PC composition
> > below), I need to share IRQ11 between the PCI graphics card
> > and the PCI lan card, but I get genuine Linux crashes:
> > -If having done 'ifconfig ...' I start X.
> > -If having started X ('ifconfig ...' commented where
> > appropiate on rc.d), I do 'ifconfig ...'.
> > A hard reset is needed. I use ne2k-pci as module to support
> > the lan card (clone based on Realtek 8029AS chip). The
> > relevant line is:
> > if (request_irq(dev->irq, ei_interrupt, SA_SHIRQ, dev->name,
> > dev)) return -EAGAIN;
> > But I have no idea if X servers (SVGA for Elsa Victory
> > Erazor with Riva 128) are well behaved about interrupt
> > sharing. Do you know about this? Or do you guess if I miss
> > something?
>
> That's a problem of the Riva server. It doesn't (and can't)
> install an interrupt handler. Unfortunately, it sometimes
> generates interrupts. As long as there is no kernel driver
> using this interrupt there's _no_ interrupt handler so the
> kernel disables the line and everything works well.
>
> If there is a handler (i.e. for the network card) the line is
> enabled and the false irq from the RIVA card is delivered.
> Because no handler resets the interrupt condition, it is
> delivered on and on and the system is stuck.
>
> Btw, an SMP system will only get very slow *g*
>
> Conclusion: You have to use a single IRQ for the Riva.
> Try to share interrupts between devices that have
> appropriate interrupt handlers.
>
> #ifdef FLAME
> I bet, if there were public data sheets for the riva
> the bug would have been slain long ago...
> #endif

I have a question. I've never had a riva or any other pci/agp cards except
S3 and Matrox. If you disable setting an irq in the pci bios, would this
not fix the problem? If the card is a AGP, I noticed that some bios's (all?
not sure, mine is set to disable vga irq) and there is a pci card
immediately below it, then it may have the same IRQ. I worked on a 95
machine with a wide adaptec scsi. the scsi and the video card shared the
same irq and it made 95 crawl worse than it does. Disabling irq made the
video not work on 95. Moving the scsi card down 1 slot fixed all the
problems.

I'd love to hear input. I work with winblows at work and might be useful

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