[PATCHv2 2/2] nvme-pci: remove cached shadow doorbell offsets

[John Levon]

On Thu, Oct 14, 2021 at 09:45:43AM -0700, Keith Busch wrote:

> And when this feature is in use, the specification requires all queue
> updates use this mechanism, so don't don't treat the admin queue
> differently.

Hi Keith, I think you might have missed the other email from me?

This would cause implementation difficulties for a controller, right?
Currently we presume that the admin queue's shadow doorbells aren't valid, so
always look at the BAR0 location. Given we need to support older Linux versions,
we don't have any non-hacky way to handle this: we'd need something horrible
that presumes those Linux versions - and any other driver implementations -
always leave the admin queue shadows at zero, so if we see a non-zero value, it
must be doing shadow doorbells.

It's unclear to me what the advantage of fixing this is, given Linux has been
out of spec for so long.

regards
john