Re: [PATCH] Tweak re-routing of PCI interrupts

On Fri, Jun 06, 2003 at 12:36:54PM -0600, M. Warner Losh wrote:
> In message: <XFMail.20030606141331.jhb_at_FreeBSD.org>
>             John Baldwin <jhb_at_FreeBSD.org> writes:
> : I have a small tweak to the PCI code that re-routes PCI interrupts.
> : Basically, it does two things, 1) make the comment less ia64-specific
> : and 2) if the interrupt route returns an invalid IRQ (i.e. 255), then
> : we don't change the intline.  In other words, if we can't route the
> : interrupt, we just assume that the firmware knows more than we do and
> : go with the value it stuck in the register.  1) is a no-brainer, but
> : I wonder what people think about 2).  Patch below:
> 
> I think #2 isn't so good.  #1 is a no-brainer :-)
> 
> :  #if ...
> ...
> : +               irq = PCIB_ROUTE_INTERRUPT(pcib, dev, cfg->intpin);
> : +               if (PCI_INTERRUPT_VALID(irq))
> : +                       cfg->intline = irq;
> : +               else
> :  #endif
> : +                       irq = cfg->intline;
> : +               resource_list_add(rl, SYS_RES_IRQ, 0, irq, irq, 1);
> :         }
> :  }
> 
> The part I don't like is that if we can't route an interrupt, we
> assume that the interrupt that was written there before is good and
> routed.  This strikes me as an unwise assumption.  Also, we haven't

Unless you find a reliable way to ask the BIOS how the board is wired,
whatelse would you do than trust the inline register?

> recorded our info in the underlying pci register.  Don't know if that
> will matter for other OSes that are booted after we are.

-- 
B.Walter                   BWCT                http://www.bwct.de
ticso_at_bwct.de                                  info_at_bwct.de