Re: [Qemu-devel] [PATCH] msi/msix: added public API to set/get MSI message address, and data

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-06-21 12:28, Alexey Kardashevskiy wrote:
> On 21/06/12 17:39, Jan Kiszka wrote:
>> On 2012-06-21 09:18, Alexey Kardashevskiy wrote:
>>>
>>> agrhhh. sha1 of the patch changed after rebasing :)
>>>
>>>
>>>
>>> Added (msi|msix)_(set|get)_message() function for whoever might
>>> want to use them.
>>>
>>> Currently msi_notify()/msix_notify() write to these vectors to
>>> signal the guest about an interrupt so the correct values have to
>>> written there by the guest or QEMU.
>>>
>>> For example, POWER guest never initializes MSI/MSIX vectors, instead
>>> it uses RTAS hypercalls. So in order to support MSIX for virtio-pci on
>>> POWER we have to initialize MSI/MSIX message from QEMU.
>>>
>>> As only set* function are required by now, the "get" functions were added
>>> or made public for a symmetry.
>>>
>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>> ---
>>>  hw/msi.c  |   29 +++++++++++++++++++++++++++++
>>>  hw/msi.h  |    2 ++
>>>  hw/msix.c |   11 ++++++++++-
>>>  hw/msix.h |    3 +++
>>>  4 files changed, 44 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/msi.c b/hw/msi.c
>>> index 5233204..9ad84a4 100644
>>> --- a/hw/msi.c
>>> +++ b/hw/msi.c
>>> @@ -105,6 +105,35 @@ static inline uint8_t msi_pending_off(const PCIDevice* dev, bool msi64bit)
>>>      return dev->msi_cap + (msi64bit ? PCI_MSI_PENDING_64 : PCI_MSI_PENDING_32);
>>>  }
>>>  
>>> +MSIMessage msi_get_message(PCIDevice *dev)
>>
>> MSIMessage msi_get_message(PCIDevice *dev, unsigned vector)
> 
> 
> Who/how/why is going to calculate the vector here?
> 
>>
>>> +{
>>> +    uint16_t flags = pci_get_word(dev->config + msi_flags_off(dev));
>>> +    bool msi64bit = flags & PCI_MSI_FLAGS_64BIT;
>>> +    MSIMessage msg;
>>> +
>>> +    if (msi64bit) {
>>> +        msg.address = pci_get_quad(dev->config + msi_address_lo_off(dev));
>>> +    } else {
>>> +        msg.address = pci_get_long(dev->config + msi_address_lo_off(dev));
>>> +    }
>>> +    msg.data = pci_get_word(dev->config + msi_data_off(dev, msi64bit));
>>
>> And I have this here in addition:
>>
>>     unsigned int nr_vectors = msi_nr_vectors(flags);
>>     ...
>>
>>     if (nr_vectors > 1) {
>>         msg.data &= ~(nr_vectors - 1);
>>         msg.data |= vector;
>>     }
>>
>> See PCI spec and existing code.
> 
> 
> What for? I really do not get it why someone might want to read something but not real value.
> What PCI code should I look?

I'm not sure what your use case for reading the message is. For KVM
device assignment it is preparing an alternative message delivery path
for MSI vectors. And for this we will need vector notifier support for
MSI as well. You can check the MSI-X code for corresponding use cases of
msix_get_message.

And when we already have msi_get_message, another logical use case is
msi_notify. See msix.c again.

Jan

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