[Qemu-devel] PCI IRQ routing problems

[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

Re: [Qemu-devel] PCI IRQ routing problems

[Fabrice Bellard]

Ed Swierk wrote:
> 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.
> [...]
> 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.

I did not study the issue yet, but I suspect it is a Bochs BIOS issue (I 
remember it declares a limited number of PCI slots for example).

IMHO, all the PCI, MP table and ACPI table init should be moved to the 
Bochs BIOS. I did not do it because it was not strictly necessary to 
have something that works. A simple way to do that is to copy the 
relevant QEMU code in a separate section of the Bochs BIOS and to 
execute it by switching temporarily to 32 bit protected mode in the BIOS 
init code.

Fabrice.