Re: [PATCH] PCI: Add no-D3 quirk for Mellanox ConnectX-[45]

From: David Gibson <david@gibson.dropbear.id.au>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
	davem@davemloft.net, saeedm@mellanox.com, ogerlitz@mellanox.com,
	tariqt@mellanox.com, bhelgaas@google.com,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	netdev@vger.kernel.org, alex.williamson@redhat.com,
	linux-pci@vger.kernel.org, linux-rdma@vger.kernel.org,
	sbest@redhat.com, paulus@samba.org,
	Alexey Kardashevskiy <aik@au1.ibm.com>
Subject: Re: [PATCH] PCI: Add no-D3 quirk for Mellanox ConnectX-[45]
Date: Wed, 9 Jan 2019 16:30:45 +1100	[thread overview]
Message-ID: <20190109053045.GE6682@umbus.fritz.box> (raw)
In-Reply-To: <012d24d58a542ed44c8af9f517f1bd61ab912037.camel@kernel.crashing.org>

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On Wed, Jan 09, 2019 at 04:09:02PM +1100, Benjamin Herrenschmidt wrote:
> On Mon, 2019-01-07 at 21:01 -0700, Jason Gunthorpe wrote:
> > 
> > > In a very cryptic way that requires manual parsing using non-public
> > > docs sadly but yes. From the look of it, it's a completion timeout.
> > > 
> > > Looks to me like we don't get a response to a config space access
> > > during the change of D state. I don't know if it's the write of the D3
> > > state itself or the read back though (it's probably detected on the
> > > read back or a subsequent read, but that doesn't tell me which specific
> > > one failed).
> > 
> > If it is just one card doing it (again, check you have latest
> > firmware) I wonder if it is a sketchy PCI-E electrical link that is
> > causing a long re-training cycle? Can you tell if the PCI-E link is
> > permanently gone or does it eventually return?
> 
> No, it's 100% reproducable on systems with that specific card model,
> not card instance, and maybe different systems/cards as well, I'll let
> David & Alexey comment further on that.

Well, it's 100% reproducable on a particular model of system
(garrison) with a particular model of card.  I've had some suggestions
that it fails with some other systems card card models, but nothing
confirmed - the one other system model I've been able to try, which
also had a newer card model didn't reproduce the problem.

> > Does the card work in Gen 3 when it starts? Is there any indication of
> > PCI-E link errors?
> 
> Nope.
> 
> > Everytime or sometimes?
> > 
> > POWER 8 firmware is good? If the link does eventually come back, is
> > the POWER8's D3 resumption timeout long enough?
> > 
> > If this doesn't lead to an obvious conclusion you'll probably need to
> > connect to IBM's Mellanox support team to get more information from
> > the card side.
> 
> We are IBM :-) So far, it seems to be that the card is doing something
> not quite right, but we don't know what. We might need to engage
> Mellanox themselves.

Possibly.  On the other hand, I've had it reported that this is a
software regression at least with downstream red hat kernels.  I
haven't yet been able to eliminate factors that might be confusing
that, or try to find a working version upstream.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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