[Qemu-devel] PCI IRQ routing problems

[Ed Swierk]

Linux 2.6.17 running on the latest qemu snapshot is unable to route
IRQs to more than 4 network interfaces when running without ACPI, and
is limited to 2 network interfaces with ACPI enabled.

With 8 network interfaces and ACPI disabled, I get the following
kernel output during boot:

ne2k-pci.c:v1.03 9/22/2003 D. Becker/P. Gortmaker
 http://www.scyld.com/network/ne2k-pci.html
PCI: Found IRQ 10 for device 0000:00:03.0
eth0: RealTek RTL-8029 found at 0xc100, IRQ 10, 52:54:00:12:34:56.
PCI: Found IRQ 11 for device 0000:00:04.0
PCI: Sharing IRQ 11 with 0000:00:01.2
eth1: RealTek RTL-8029 found at 0xc200, IRQ 11, 52:54:00:12:34:57.
PCI: Found IRQ 9 for device 0000:00:05.0
eth2: RealTek RTL-8029 found at 0xc300, IRQ 9, 52:54:00:12:34:58.
PCI: Found IRQ 5 for device 0000:00:06.0
eth3: RealTek RTL-8029 found at 0xc400, IRQ 5, 52:54:00:12:34:59.
eth4: RealTek RTL-8029 found at 0xc500, IRQ 11, 52:54:00:12:34:5A.
eth5: RealTek RTL-8029 found at 0xc600, IRQ 9, 52:54:00:12:34:5B.
eth6: RealTek RTL-8029 found at 0xc700, IRQ 11, 52:54:00:12:34:5C.
eth7: RealTek RTL-8029 found at 0xc800, IRQ 9, 52:54:00:12:34:5D.

The missing "Found IRQ" messages for eth4 through eth7 indicate that
IRQs won't get routed properly. Indeed, later on the kernel emits
complaints like: "irq 11: nobody cared ... Disabling IRQ #11".

With 3 network interfaces and ACPI enabled, I get slightly different output:

ne2k-pci.c:v1.03 9/22/2003 D. Becker/P. Gortmaker
 http://www.scyld.com/network/ne2k-pci.html
PCI: Found IRQ 9 for device 0000:00:03.0
eth0: RealTek RTL-8029 found at 0xc100, IRQ 9, 52:54:00:12:34:56.
PCI: Found IRQ 11 for device 0000:00:04.0
PCI: Sharing IRQ 11 with 0000:00:01.2
eth1: RealTek RTL-8029 found at 0xc200, IRQ 11, 52:54:00:12:34:57.
PCI: Found IRQ 10 for device 0000:00:05.0
IRQ routing conflict for 0000:00:01.3, have irq 9, want irq 10
eth2: RealTek RTL-8029 found at 0xc300, IRQ 10, 52:54:00:12:34:58.
piix4_smbus 0000:00:01.3: Found 0000:00:01.3 device
piix4_smbus 0000:00:01.3: SMB base address uninitialized - upgrade
BIOS or use force_addr=0xaddr

Only eth0 and eth1 end up working.

I suspect the problem in the non-ACPI case is caused by a limitation
in the PCI IRQ routing table in the Bochs BIOS, but I haven't a clue
how to fix it. Any ideas would be appreciated.

--Ed