Re: [Qemu-devel] [PATCH 0/2] RFC: powerpc-vfio: adding support

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 12/07/12 14:31, Alex Williamson wrote:
> On Thu, 2012-07-12 at 14:16 +1000, Alexey Kardashevskiy wrote:
>> On 12/07/12 12:54, Alex Williamson wrote:
>>> On Wed, 2012-07-11 at 12:25 +1000, Alexey Kardashevskiy wrote:
>>>> On 11/07/12 02:57, Alex Williamson wrote:
>>>>> On Tue, 2012-07-10 at 15:51 +1000, Alexey Kardashevskiy wrote:
>>>>>> The two patches in this set are supposed to add VFIO support for POWER.
>>>>>>
>>>>>> The first one adds one more step in the initalizaion sequence which I am not
>>>>>> sure is correct.
>>>>>>
>>>>>> The second patch adds actual VFIO support. It is not ready to submit but
>>>>>> ready to discuss. I would like to get rid of all #ifdef TARGET_PPC64 in patch #2
>>>>>> and I wonder if there is any plan to implement some generic EOI support code, etc.
>>>>>
>>>>> A generic EOI notifier is on my todo list, but I have no idea what it's
>>>>> going to look like.  As you know, I've got an ioapic specific notifier
>>>>> in my tree, you add a spapr specific one.  I welcome ideas on how to
>>>>> create something generic that has a chance of being accepted.  Thanks,
>>>>
>>>>
>>>> So far the only platform specific call is xxxx_add_gsi_eoi_notifier. The
>>>> xxxx_remove_gsi_eoi_notifier only calls notifier_remove, you've got to fix yours
>>>> ioapic_remove_gsi_eoi_notifier() as it does too much :)
>>>>
>>>>
>>>> The only place for placing "add_eoi" callback I can see right now is QEMUMachine as there is no
>>>> unified machine interrupt controller - IOAPIC has its own type TYPE_IOAPIC_COMMON and XICS is not
>>>> even a SysBusDevice. And the callback is not specific for any kind of bus so it cannot go to PCIBus.
>>>>
>>>> Does it sound reasonable?
>>>
>>> I suspect we'd need to somehow tie it into qemu_irq where both handlers
>>> and notifiers are allocated so we don't really care the underlying
>>> implementation.  Something like qemu_add_irq_eoi_notifier(qemu_irq
>>> irq, ...).  It's another mess like adding the PCIBus interrupt line to
>>> gsi effort though.  Thanks,
>>
>>
>> Tried. Added add_eoi_notifier() callback to qemu_irq, new IRQ allocator:
>> qemu_irq *qemu_allocate_irqs2(qemu_irq_handler handler, void *opaque, int n,
>>                               qemu_eoi_add_notifier add_notifier);
>> and called it from the XICS initialization code.
>>
>> It could work out if pci_get_irq() or pci_route_irq_fn() returned qemu_irq but no, they just return
>> a global IRQ number (pure or embedded in a struct) and there is no common way to resolve qemu_irq
>> (and then add_eoi_notifier()) from that number within vfio_pci.
> 
> Well GSI and qemu_irq are different address spaces.  We still need GSI
> for any kind of qemu bypass case.

No, that is ok, we also need GSI because XICS and IOAPIC need it in the end.

>> May be we could add the callback pointer into PCIINTxRoute?
> 
> Maybe, but why is this PCI specific?  Can't we call it as
> qemu_add_irq_eoi_notifier(pdev->irq[0], Notifier)?  That would work much
> like qemu_set_irq, extracting the irq number from the IRQState and
> passing it through to the add_notifier callback for IRQState until it
> got to the ioapic/pic/xics.
> 
> int qemu_add_irq_eoi_notifier(qemu_irq *irq, Notifier notifier)
> {
>     if (!irq || !irq->add_eoi_notifier)
>         return -1;
> 
>    return irq->add_eoi_notifier(irq->opaque, irq->n, notifier);
> }
> 

Then we will have to entirely replace qemu_allocate_irqs() with qemu_allocate_irqs2() and pass some
non-zero add_eoi_notifier() on every level, at least for PCI for now. I would like to avoid that if
possible - hard to get accepted :)


-- 
Alexey