Re: [Qemu-devel] [PATCH 00/10] Fix versatile_pci (and break versatilepb linux guests!)

[Arnd Bergmann <arnd@arndb.de>]

On Sunday 24 March 2013, Peter Maydell wrote:
> Yeah, ideally being able to detect the buggy kernel would be good;
> I can't see anything at the controller level that would do though,
> and I don't really know enough about PCI to know about generic
> PCI stuff that would work. (Why would the OS need to tell the
> device anything about its IRQ if it's hardwired?)

I think it actually does on versatile and other platforms on which
the kernel probes the PCI bus itself, rather than relying on firmware
to have resources assigned in advance.

IIRC, the PCI_INTERRUPT_LINE pci config space byte (0x3c) is purely
informational and used as a way to communicate the interrupt number
from the bus scan code (assumed to be a PC BIOS in the PCI spec,
but drivers/pci/setup-irq.c in case of versatile+linux) to a device
driver.

So the kernel should actually write the proper interrupt number in
there. In future kernels, this may not necessarily be the hardware
number, but today it is. Can you try out what the kernel writes into
that register in qemu, with and without my patches?

I would expect the numbers to be (64+27) to (64+30), since we
linearize the interrupt numbers so that VIC gets 32 through
63 and SIC gets 64 through 95.

	Arnd