Re: PCIe MSI address is not written at pci_enable_msi_range call

[Marc Zyngier]

On 13/07/16 07:22, Bharat Kumar Gogada wrote:
>> Subject: Re: PCIe MSI address is not written at pci_enable_msi_range call
>>
>> On 11/07/16 10:33, Bharat Kumar Gogada wrote:
>>> Hi Marc,
>>>
>>> Thanks for the reply.
>>>
>>> From PCIe Spec:
>>> MSI Enable Bit:
>>> If 1 and the MSI-X Enable bit in the MSI-X Message Control register
>>> (see Section 6.8.2.3) is 0, the function is permitted to use MSI to
>>> request service and is prohibited from using its INTx# pin.
>>>
>>> From Endpoint perspective, MSI Enable = 1 indicates MSI can be used
>> which means MSI address and data fields are available/programmed.
>>>
>>> In our SoC whenever MSI Enable goes from 0 --> 1 the hardware latches
>> onto MSI address and MSI data values.
>>>
>>> With current MSI implementation in kernel, our SoC is latching on to
>>> incorrect address and data values, as address/data are updated much later
>> than MSI Enable bit.
>>
>> As a side question, how does setting the affinity work on this end-point if this
>> involves changing the address programmed in the MSI registers?
>> Do you expect the enabled bit to be toggled to around the write?
>>
> 
> Yes,

Well, that's pretty annoying, as this will not work either. But maybe
your MSI controller has a single doorbell? You haven't mentioned which
HW that is...

> Would anybody change MSI address in between wouldn't it cause race condition ?

Changing the affinity of an interrupt is always racy, and the kernel
deals with it.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...