[coreboot] v3 IRQ table strangeness

Tom Sylla tsylla at gmail.com
Fri May 9 03:15:57 CEST 2008

ron minnich wrote:
> On Thu, May 8, 2008 at 3:30 PM, Carl-Daniel Hailfinger <
>> So PCI IDs and bus location of the interrupt router in the PIRQ table
>> have no meaning at all for Geode?
> No, because linux (and who knows what else) don't even know what it is.
> At present, the PIRQ is only used by coreboot!

Well, Linux *could* know about it, with not too much work. 5536 and 5536 
have the same router interface as 5530 and therefore 5520 (the emulated 
in vsa stuff from an earlier thread). Linux knows about the 5520 and how 
to use it. The goal of the "Compatible PCI Interrupt Router" field in 
the tables is so an OS can have one driver, and use it for multiple 
routers. Linux does not actually use that field, it looks like it just 
checks device ID. 5535 and 5536 could be added in the same way as 5530 
was in this patch:


which is linked from coreboot's wiki.

So, you could do it pretty easily. I don't know what advantage there is 
to letting Linux steer IRQs on a geode, though. Plus, 5536 v3 coreboot 
PIRQ tables have one IRQ in their bitmaps, and no PCI exclusive (as Marc 
pointed out), so the router doesn't matter anyway.

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