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From: Bjorn Helgaas <firstname.lastname@example.org>
To: Alex Williamson <email@example.com>
Cc: Sinan Kaya <firstname.lastname@example.org>, Jason Gunthorpe <email@example.com>,
Bjorn Helgaas <firstname.lastname@example.org>,
Mike Marciniszyn <email@example.com>,
Dennis Dalessandro <firstname.lastname@example.org>,
Doug Ledford <email@example.com>,
"open list:HFI1 DRIVER" <firstname.lastname@example.org>,
open list <email@example.com>,
Alex Deucher <firstname.lastname@example.org>,
Rajat Jain <email@example.com>
Subject: Re: [PATCH 1/2] IB/hfi1: Try slot reset before secondary bus reset
Date: Mon, 23 Apr 2018 15:23:11 -0500 [thread overview]
Message-ID: <20180423202311.GA164898@bhelgaas-glaptop.roam.corp.google.com> (raw)
On Mon, Apr 23, 2018 at 01:10:44PM -0600, Alex Williamson wrote:
> On Mon, 23 Apr 2018 13:28:22 -0400
> Sinan Kaya <firstname.lastname@example.org> wrote:
> > On 4/20/2018 11:04 AM, Alex Williamson wrote:
> > > Is there a concern here about whether the endpoint device driver or the
> > > PCI core really knows better about link retraining? This makes me
> > > remember my unfinished (and need to revisit) Pericom quirk where
> > > errata in the PCIe switch requires that upstream and downstream links
> > > are balanced (ie. same link rate) or else enabling ACS results in
> > > packets not properly flowing through the switch. If an endpoint driver
> > > starts deciding to retrain links, overriding quirks in the PCI core,
> > > then such topology manipulation isn't possible. Why does the
> > > driver .probe() function think it can retrain at a higher link rate
> > > than PCI core? Thanks,
> > The example given is for some serdes firmware load to happen in probe and
> > then performing a retrain to reach to a better speed.
> > It becomes a chicken and egg problem.
> > 1. Endpoint HW trains to gen1 by default pre-boot.
> > 2. PCI core enumerates the device.
> > 3. Endpoint driver gets loaded
> > 4. Driver does the firmware programming followed by a link retrain.
> > I think it is the responsibility of the PCI core to provide reset APIs.
> > However, expecting endpoint drivers to be knowledgeable about hotplug is
> > too much.
> > We can certainly contain AER change into pci directory by moving the slot
> > reset function to drivers/pci.h file.
> > But, we need to think about what to do about VFIO and other endpoint
> > initiated reset cases. My suggestion was to move this into a single API and
> > remove all other APIs from include/linux/pci.h.
> I'm a little confused about the relation between reset and retrain.
> AIUI we can retrain the link without any sort of endpoint reset and if
> some sort of driver/firmware setup is required on the endpoint to
> achieve the target link speed, then I'd think we only want to retrain.
In hfi1, do_pcie_gen3_transition() resets the device. I don't know if
retraining the link would be sufficient; maybe the reset is required
to make the device use the new firmware. I guess we already export
reset interfaces, so if we add a retrain interface, drivers could
choose what they need.
> How this is going to work with vfio is an interesting question. We're
> only providing access to the device, not the link to the device.
> Multifunction endpoints become a big problem if one function starts
> requesting link retraining while another is in use elsewhere.
Can we just make it the driver's problem by returning -EPERM if one
function requests a retrain while another function is in use?
next prev parent reply other threads:[~2018-04-23 20:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-19 19:56 Sinan Kaya
2018-04-19 19:56 ` [PATCH 2/2] PCI/AER: " Sinan Kaya
2018-04-27 18:51 ` Sinan Kaya
2018-04-19 20:26 ` [PATCH 1/2] IB/hfi1: " Jason Gunthorpe
2018-04-19 20:35 ` Sinan Kaya
2018-04-19 21:47 ` Bjorn Helgaas
2018-04-19 22:11 ` Deucher, Alexander
2018-04-20 14:12 ` Dennis Dalessandro
2018-04-20 14:55 ` Jason Gunthorpe
2018-04-19 22:19 ` Sinan Kaya
2018-04-20 14:00 ` Bjorn Helgaas
2018-04-20 14:23 ` Sinan Kaya
2018-04-20 15:04 ` Alex Williamson
2018-04-23 17:28 ` Sinan Kaya
2018-04-23 19:10 ` Alex Williamson
2018-04-23 20:17 ` Sinan Kaya
2018-04-23 20:23 ` Bjorn Helgaas [this message]
2018-04-23 20:41 ` Alex Williamson
2018-04-25 14:13 ` Sinan Kaya
2018-04-20 14:54 ` Jason Gunthorpe
2018-06-19 21:43 ` Bjorn Helgaas
2018-06-19 22:21 ` Sinan Kaya
2018-06-22 14:01 ` Bjorn Helgaas
2018-06-22 16:04 ` Sinan Kaya
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