linux-kernel - Re: [PATCH 2/2] pci: Don't set RCB bit in LNKCTL if the upstream bridge hasn't

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Date:   Mon, 14 Nov 2016 12:56:04 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Alexander Graf <agraf@...e.de>,
        Hannes Reinecke <hare@...e.de>, Don Dutile <ddutile@...hat.com>
Subject: Re: [PATCH 2/2] pci: Don't set RCB bit in LNKCTL if the upstream
 bridge hasn't

On Wed, Nov 09, 2016 at 11:11:40AM -0600, Bjorn Helgaas wrote:
> Hi Johannes,
> 
> On Wed, Nov 02, 2016 at 04:35:52PM -0600, Johannes Thumshirn wrote:
> > The Read Completion Boundary (RCB) bit must only be set on a device or
> > endpoint if it is set on the root complex.
> > 
> > Certain BIOSes erroneously set the RCB Bit in their ACPI _HPX Tables
> > even if it is not set on the root port. This is a violation to the PCIe
> > Specification and is known to bring some Mellanox Connect-X 3 HCAs into
> > a state where they can't map their firmware and go into error recovery.
> > 
> > BIOS Information
> > 	Vendor: IBM
> > 	Version: -[A8E120CUS-1.30]-
> > 	Release Date: 08/22/2016
> 
> This seems like a pretty serious problem (sounds like maybe the HCA is
> completely useless?)

Correct.

> 
> Can you point us at a bugzilla or other problem report?  It's nice to
> have details of what this looks like to a user, so people who trip
> over this problem have a little more chance of finding the solution.

As we already said, our bugzilla entry for this is not accessible from the
outside, but I know Red Hat does have a bugzilla entry for the same issue as
well. Maybe this is reachable from the outside (adding Don for this, as I know
he has worked on this problem as well).

> 
> 7a1562d4f2d0 ("PCI: Apply _HPX Link Control settings to all devices
> with a link") appeared in v3.18, so it's probably not a *new* problem,
> so my guess is that this is v4.10 material.

Yes 4.10 sounds good to me. I personally think, this problem hasn't
materialized yet, as this is the kind of hardware you run on a rather /stable/
kernel either you built on your own or get from an enterprise distribution and
until recently these kernels haven't been updated to something newer than
3.18.

Thanks,
	Johannes

-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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