Re: IRQS on 6 Slot Macs

On Mon, 3 Nov 2003, Bob Brose wrote:

User Benjamin Herrenschmidt says:

quoted

On Mon, 2003-11-03 at 14:35, Robert E Brose II wrote:

quoted

A couple of things right off, the rage128 appears to be the only thing on
irq 23 however 23 doesn't show up in /proc/interrupts meaning, I suppose,
that it's not using the interrupt. So why does the drm complain?

How come everything from slots 3-6 says it's on the same interrupt (25)?

I don't know what's up with the DRM not liking your interrupt. I can
answer for the sharing of USB, symbios and firewire interrupts: all 3
slots share one interrupt because of bad motherboard design :)
Basicallly, what they did when designing that machine was to use a
standard powersurge design with 3 slots and replace one of them
with a PCI<->PCI bridge. Since they didn't "know" how to get more
interrupt lines out of Grand Central, they just also stuffed all
interrupt lines together for those 4 slots (I'm pretty sure GC do

Tsss... They could at least have `swizzled' the lines...

quoted

have spare lines they could have used, but that would have meant
updating Open Firmware to understand the layout, I doubt the people
who designed that machine wanted to dive into that).

Ben.

I suppose then that I should reorder the cards so that the ones generating
the most interrupts would be in the first 2 slots? It's pretty funny
having the possibility of the use of lots of irqs then ending up with
x86 style sharing. :(

Yes, try to spread out interrupts evenly across interrupt lines.
Furthermore the presence of the bridge will probably incur a slight slowdown
for the last 3 slots, too. Don't know whether it's significant (should reread
PCI specs first).

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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