Re: [Qemu-devel] [PATCH 1/3] msi/msix: added functions to API to set up message address and data

[Jan Kiszka]

On 2012-06-14 07:17, Alexey Kardashevskiy wrote:
> On 14/06/12 14:56, Alex Williamson wrote:
>> On Thu, 2012-06-14 at 14:31 +1000, Alexey Kardashevskiy wrote:
>>> Normally QEMU expects the guest to initialize MSI/MSIX vectors.
>>> However on POWER the guest uses RTAS subsystem to configure MSI/MSIX and
>>> does not write these vectors to device's config space or MSIX BAR.
>>>
>>> On the other hand, msi_notify()/msix_notify() write to these vectors to
>>> signal the guest about an interrupt so we have to write correct vectors
>>> to the devices in order not to change every user of MSI/MSIX.
>>>
>>> The first aim is to support MSIX for virtio-pci on POWER. There is
>>> another patch for POWER coming which introduces a special memory region
>>> where MSI/MSIX vectors point to.
>>>
>>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>> ---
>>>  hw/msi.c  |   14 ++++++++++++++
>>>  hw/msi.h  |    1 +
>>>  hw/msix.c |   10 ++++++++++
>>>  hw/msix.h |    3 +++
>>>  4 files changed, 28 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/hw/msi.c b/hw/msi.c
>>> index 5d6ceb6..124878a 100644
>>> --- a/hw/msi.c
>>> +++ b/hw/msi.c
>>> @@ -358,3 +358,17 @@ unsigned int msi_nr_vectors_allocated(const PCIDevice 
>>> *dev)
>>>      uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
>>>      return msi_nr_vectors(flags);
>>>  }
>>> +
>>> +void msi_set_address_data(PCIDevice *dev, uint64_t address, uint16_t data)
>>> +{
>>> +    uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
>>> +    bool msi64bit = flags & PCI_MSI_FLAGS_64BIT;
>>> +
>>> +    if (msi64bit) {
>>> +        pci_set_quad(dev->config + msi_address_lo_off(dev), address);
>>> +    } else {
>>> +        pci_set_long(dev->config + msi_address_lo_off(dev), address);
>>> +    }
>>> +    pci_set_word(dev->config + msi_data_off(dev, msi64bit), data);
>>> +}
>>
>> Why not make it msi_set_message() and pass MSIMessage?  I'd be great if
>> you tossed in a msi_get_message() as well, I think we need it to be able
>> to do a kvm_irqchip_add_msi_route() with MSI.  Thanks,
> 
> 
> I am missing the point. What is that MSIMessage?
> It is just an address and data, making a struct from this is a bit too much :)

This is about consistent APIs. In practice (assembly), MSIMessage will
make no difference from open-coded address/data tuples, but it is
cleaner to pass around. Please follow the existing patterns.

> I am totally unfamiliar with kvm_irqchip_add_msi_route to see the bigger 
> picture, sorry.

The kvm_irqchip_* API come into play when you implement some interrupt
controller models in the kernel for performance reasons. We have this on
x86, we will see it on Book3E and ARM soon. You are targeting Book3S,
right? Not sure what the plans are there.

And, yes, msi_get_message() will be needed soon as well, at latest when
I push vector notifiers for classic MSI. If you have a need for reading
the message back, please add this helper already.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux