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

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Date:   Fri, 20 Apr 2018 10:12:28 -0400
From:   Dennis Dalessandro <dennis.dalessandro@...el.com>
To:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     Sinan Kaya <okaya@...eaurora.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "sulrich@...eaurora.org" <sulrich@...eaurora.org>,
        "timur@...eaurora.org" <timur@...eaurora.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        "open list:HFI1 DRIVER" <linux-rdma@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] IB/hfi1: Try slot reset before secondary bus reset

On 4/19/2018 6:11 PM, Deucher, Alexander wrote:
>> -----Original Message-----
>> From: Bjorn Helgaas [mailto:helgaas@...nel.org]
>> Sent: Thursday, April 19, 2018 5:47 PM
>> To: Jason Gunthorpe <jgg@...pe.ca>
>> 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>; Deucher, Alexander
>> <Alexander.Deucher@....com>
>> Subject: Re: [PATCH 1/2] IB/hfi1: Try slot reset before secondary bus reset
>>
>> [+cc Alex, who might know why DRM drivers have their own PCIe Gen3
>> code]
>>
>> On Thu, Apr 19, 2018 at 02:26:32PM -0600, Jason Gunthorpe wrote:
>>> On Thu, Apr 19, 2018 at 03:56:23PM -0400, Sinan Kaya wrote:
>>>> The infiniband adapter might be connected to a PCI hotplug slot.
>>>> Performing secondary bus reset on a hotplug slot causes PCI link
>> up/down interrupts.
>>>>
>>>> Hotplug driver removes the device from system when a link down
>>>> interrupt is observed and performs re-enumeration when link up
>> interrupt is observed.
>>>>
>>>> This conflicts with what this code is trying to do. Try secondary
>>>> bus reset only if pci_reset_slot() fails/unsupported.
>>>>
>>>> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
>>>> drivers/infiniband/hw/hfi1/pcie.c | 3 ++-
>>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/infiniband/hw/hfi1/pcie.c
>>>> b/drivers/infiniband/hw/hfi1/pcie.c
>>>> index 83d66e8..75f49e3 100644
>>>> +++ b/drivers/infiniband/hw/hfi1/pcie.c
>>>> @@ -908,7 +908,8 @@ static int trigger_sbr(struct hfi1_devdata *dd)
>>>
>>> The code above this hunk is:
>>>
>>> /*
>>>   * Trigger a secondary bus reset (SBR) on ourselves using our parent.
>>>   *
>>>   * Based on pci_parent_bus_reset() which is not exported by the
>>>   * kernel core.
>>>   */
>>> static int trigger_sbr(struct hfi1_devdata *dd) {
>>>
>>> [..]
>>>
>>> This really seems like something the PCI core should be helping with,
>>> drivers shouldn't be doing stuff like this. I get the feeling this
>>> should be a common need if drivers support various error recovery
>>> schemes?
>>>
>>> Bjorn, would be appropriate to export pci_parent_bus_reset() or some
>>> variation therin??
>>
>> I agree it would be really nice if the PCI core could help out somehow so we
>> could get some of this code out of individual drivers.
>>
>> If fact, stepping back a few paces, this HFI reset path is part of a transition to
>> PCIe gen3 signaling, and I'm not sure why *that* is in the driver either.
>>
>> There's an ongoing discussion [1] about why this gen3 code is in the driver.
>> Several DRM drivers include similar code (cik_pcie_gen3_enable(),
>> si_pcie_gen3_enable()).
>>
>> 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.
> 
> My understanding was that some platfoms only bring up the link in gen 1 mode for compatibility reasons.  TBH, I'm not that familiar with how the links come up on different platforms.
> 
> Alex
> 

I'm checking with our HW folks and the guys that wrote the PCI code in 
our driver. I quite frankly just don't recall what all is going on here. 
Let me find out for sure before I give out wrong information.

-Denny