Re: [PATCH v3] nvme-pci: Support shared tags across queues for Apple 2018 controllers

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2019-07-30 at 09:30 -0600, Keith Busch wrote:
> On Fri, Jul 19, 2019 at 03:31:02PM +1000, Benjamin Herrenschmidt wrote:
> > From 8dcba2ef5b1466b023b88b4eca463b30de78d9eb Mon Sep 17 00:00:00 2001
> > From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Date: Fri, 19 Jul 2019 15:03:06 +1000
> > Subject: 
> > 
> > Another issue with the Apple T2 based 2018 controllers seem to be
> > that they blow up (and shut the machine down) if there's a tag
> > collision between the IO queue and the Admin queue.
> > 
> > My suspicion is that they use our tags for their internal tracking
> > and don't mix them with the queue id. They also seem to not like
> > when tags go beyond the IO queue depth, ie 128 tags.
> > 
> > This adds a quirk that marks tags 0..31 of the IO queue reserved
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> 
> One problem is that we've an nvme parameter, io_queue_depth, that a user
> could set to something less than 32, and then you won't be able to do
> any IO. I'd recommend enforce the admin queue to QD1 for this device so
> that you have more potential IO tags.

Makes sense, I don't think we care much about the number of admin tags 
on these devices.

I'm travelling, not sure I'll be able to respin & test before next
week.

Thanks.

Cheers,
Ben.