Re: [PATCH v3 4/4] hw/nvme: add polling support

[Jinhao Fan]

at 7:10 PM, Klaus Jensen <its@irrelevant.dk> wrote:

> This doesn't do what you expect it to. By not updaring the eventidx it
> will fall behind the actual head, causing the host to think that the
> device is not processing events (but it is!), resulting in doorbell
> ringing.

I’m not sure I understand this correctly. 

In 7.13.1 in NVMe Spec 1.4c it says "If updating an entry in the Shadow
Doorbell buffer **changes** the value from being less than or equal to the
value of the corresponding EventIdx buffer entry to being greater than that
value, then the host shall also update the controller's corresponding
doorbell register to match the value of that entry in the Shadow Doorbell
buffer.”

So my understanding is that once the eventidx falls behind the actual head,
the host will only ring the doorbell once but *not* for future submissions.

Is this not what real hosts are doing?