Re: [Qemu-devel] [PATCH v2 8/8] spapr_pci: Use XICS interrupt allocator and do not cache interrupts in PHB

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/21/2014 06:40 PM, Alexander Graf wrote:
> 
> On 15.05.14 11:59, Alexey Kardashevskiy wrote:
>> Currently SPAPR PHB keeps track of all allocated MSI/MISX interrupt as
>> XICS used to be unable to reuse interrupts which becomes a problem for
>> dynamic MSI reconfiguration which is happening on guest driver reload or
>> PCI hot (un)plug. Another problem is that PHB has a limit of devices
>> supporting MSI/MSIX (SPAPR_MSIX_MAX_DEVS=32) and there is no good reason
>> for that.
>>
>> This makes use of new XICS ability to reuse interrupts.
>>
>> This removes cached MSI configuration from SPAPR PHB so the first IRQ number
>> of a device is stored in MSI/MSIX config space so there is no need to store
>> this anywhere else. From now on, SPAPR PHB only keeps flags telling what
>> type
>> of interrupt for which device it has configured in order to return error if
>> (for example) MSIX was enabled and the guest is trying to disable MSI which
>> it has not enabled.
>>
>> This removes a limit for the maximum number of MSIX-enabled devices per PHB,
>> now XICS and PCI bus capacity are the only limitation.
>>
>> This changes migration stream as it fixes vmstate_spapr_pci_msi::name
>> which was
>> wrong since the beginning.
>>
>> This fixed traces to be more informative.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>
>> In reality either MSIX or MSI is enabled, never both. So I could remove
>> msi/msix
>> bitmaps from this patch, would it make sense?
> 
> Is this a hard requirement? Does a device have to choose between MSIX and
> MSI or could it theoretically have both enabled? Is this a PCI limitation,
> a PAPR/XICS limitation or just a limitation of your implementation?


My implementation does not have this limitation, I asked if I can simplify
code by introducing one :)

I cannot see any reason why PCI cannot have both MSI and MSIX enabled but
it does not seem to be used by anyone => cannot debug and confirm.

PAPR spec assumes that if the guest tries enabling MSIX when MSI is already
enabled, this is a "change", not enabling both types. But it also says MSI
and MSIX vector numbers are not shared. Hm.


-- 
Alexey