Requesting an IRQ

[Deepa Srinivasan]

Thanks for your prompt response.

I made an error in my earlier post - I'm using FreeBSD 8.1 not 5.0.

I'll look into the PCI bus driver code. I've also been looking at the Xenbus
code since it does something similar to what I need.

- Deepa

On Wed, Sep 29, 2010 at 1:41 PM, John Baldwin <jhb at freebsd.org> wrote:

> On Wednesday, September 29, 2010 12:07:27 pm Deepa Srinivasan wrote:
> > I'm writing a "pseudo" device driver for FreeBSD 5.0 - i.e. there is no
> > physical device backing it. But I need to be able to send an interrupt to
> it
> > from an underlying hypervisor (KVM). FreeBSD runs as a guest OS. I have
> done
> > the same in Linux - wrote a kernel module and used the "request_irq"
> > function to allocate an unused interrupt number. When the underlying KVM
> > injects an interrupt into the guest OS, the registered interrupt handler
> > gets called as expected.
> >
> > However, in FreeBSD, I cannot find an equivalent function to
> "request_irq".
> > Going with the available documentation and sample code, I tried modifying
> a
> > PCI driver (this may be overkill for what I'm doing, but still...) and
> used
> > the bus_alloc_resource() and bus_setup_intr() functions. In my OS
> > configuration, this results in the "irq9" being allocated to my driver.
> But
> > the same IRQ is also allocated to "acpi0". Now, when I inject an
> interrupt
> > from the hypervisor, it immediately causes an "interrupt storm" and I see
> > this message continuously printed: "interrupt storm detected on irq9;
> > throttling interrupt source". This happens even without my driver being
> > loaded. In the KVM hypervisor code, I set the interrupt to "1" and
> > immediately to "0" and I know for sure that this code path is being
> > executed.
> >
> > My question is:
> > - Is it possible to write a pseudo device driver and use something like
> the
> > "request_irq" in Linux to just be able to invoke a callback function in
> the
> > driver?
> > - Is it possible to specify the interrupt number that needs to be
> allocated
> > to my device driver so I can ensure that it is not shared with anything
> > else?
>
> You can do 2), but you will need to do it by overriding what the bus thinks
> the IRQ is.  Part of the problem is that you need a way to hook up your
> fake
> IRQ to the MD interrupt code.  This may be hackish to do in 5.0 was the x86
> code does not have the interrupt source abstraction that later versions use
> to
> implement support for PCI MSI.  In newer versions you would basically
> provide
> some sort of interrupt provider similar to MSI and then use a modified PCI
> bus
> driver to allocate an interrupt from your provider and return it via
> bus_alloc_resource().
>
> --
> John Baldwin
>