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

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Date:   Tue, 16 Jul 2019 20:58:28 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...com>, Keith Busch <kbusch@...nel.org>,
        Paul Pawlowski <paul@...rm.io>
Subject: Re: [PATCH 2/3] nvme: Retrieve the required IO queue entry size
 from the controller

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.

Cheers,
Ben.