linux-kernel - Re: [PATCH 1/2] IB/hfi1: Try slot reset before secondary bus reset

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Date:   Fri, 20 Apr 2018 08:54:00 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        sulrich@...eaurora.org, timur@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        "open list:HFI1 DRIVER" <linux-rdma@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH 1/2] IB/hfi1: Try slot reset before secondary bus reset

On Thu, Apr 19, 2018 at 04:47:23PM -0500, Bjorn Helgaas wrote:
 
> I *thought* the hardware was supposed to automatically negotiate to
> the highest rate supported by both sides without any help at all from
> software.  But since several drivers have code to do it themselves, I
> wonder if I'm missing something, or maybe there's something the PCI
> core should be doing that it isn't, and the driver code is basically
> working around that PCI core deficiency.

The HW is supposed to do that, but Gen3 is electrically *hard*.

I'm not surprised that some HW has run into trouble where the driver
might have to be involved to tweak the SERDES.. eg there is now often
on-device software involved here and updating the SERDES 'firmware'
may be needed.

Jason