[tulip] Quad card shares same irq on all ports, but only the first works

Donald Becker becker@scyld.com
Thu Aug 1 14:11:02 2002

On Thu, 1 Aug 2002, Alexander Havšng wrote:

> We have a problem with quad cards on a specific motherboard where all the
> ports are assigned the same irq.
> This should be fine, but on all other motherboards we've tried, each
> port gets its own irq, when available.

Errrmm, please clarify: is the _reported_ IRQ the same, or the _actual_
There is a very common bug on x86 motherboards where the reported IRQ on
ports 2-4 is wrong.  The actual IRQ routing is the IRQ of the first port.

[[ The specific bug is in the IRQ assignment for cards behind PCI bus
bridges.  It's common because all BIOSes use the same PCI IRQ assignment
code that Intel wrote eight years ago. ]]

> Now, here comes the weird part. Only when packets arrive on the first
> port interupts are actually raised. So if the first port is not
> receiving any packets, neither will the other ones. 

Yup, that's the mostly-harmless symptom.
The bad symptom is when you have some other device on the same IRQ, and
port 2-4 is active.  An interrupt is raised from the NIC and there is
no way to clear it, so the kernel loops in the interrupt handler
dispatch.  Doh!

> We're using a 21143 quad card from Phobos, and have also tried the
> DLink DFE-570TX card, with the same results.

What driver version?  (It's likely not my release...)

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993