Re: [PATCH 2/3] nvme: Retrieve the required IO queue entry size from the controller

From: Benjamin Herrenschmidt
Date: Tue Jul 16 2019 - 06:58:47 EST

On Tue, 2019-07-16 at 11:33 +0200, Christoph Hellwig wrote:
> > > So back to the version
> > > you circulated to me in private mail that just sets q->sqes and has a
> > > comment that this is magic for The Apple controller. If/when we get
> > > standardized large SQE support we'll need to discover that earlier or
> > > do a disable/enable dance. Sorry for misleading you down this road and
> > > creating the extra work.
> >
> > I think it's still ok, let me know...
> Ok, let's go with this series then unless the other maintainers have
> objections.
> I'm still not sure if we want to queue this up for 5.3 (new hardware
> enablement) or wait a bit, though.

The main risk is if existing controllers return crap in SQES and we try
to then use that crap. The rest should essentially be NOPs.

Maybe I should add some kind of printk to warn in case we use/detect a
non-standard size. That would help diagnosing issues.