linux-kernel - Re: [PATCH v3 0/2] IB/hfi1: Cleanup PCIe link configuration

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Message-ID: <19322128-0418-fba9-ae21-df176b3fe5e0@intel.com>
Date:   Wed, 18 Apr 2018 17:53:28 -0400
From:   Dennis Dalessandro <dennis.dalessandro@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Frederick Lawler <fred@...dlawl.com>, bhelgaas@...gle.com,
        mike.marciniszyn@...el.com, dledford@...hat.com, jgg@...lanox.com,
        linux-pci@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartlomiej Dudek <bartlomiej.dudek@...el.com>
Subject: Re: [PATCH v3 0/2] IB/hfi1: Cleanup PCIe link configuration

On 4/17/2018 10:32 AM, Bjorn Helgaas wrote:
> [+cc Bartlomiej, who recently changed do_pcie_gen3_transition(), LKML]
> 
> On Mon, Apr 16, 2018 at 11:53:43PM -0700, Christoph Hellwig wrote:
>> On Mon, Apr 16, 2018 at 07:28:23PM -0500, Frederick Lawler wrote:
>>> The IB/hfi1 driver uses custom macros to configure the target link speed. Some
>>> macros were previously replaced, but not fully. This patch series addresses the
>>> configuration inconsistencies by adding PCI_EXP_LNKCTL2_TLS* macros to PCI,
>>> and then use them in the following IB/hfi1 patch.
>>
>> Btw, why is the driver configuring the PCIe link speed?  Isn't this
>> something we should be handling in the PCI core?
> 
> Good question.  I think this sort of code definitely should not be in
> drivers unless it's to work around some kind of defect in the device.
> 
> I think the intent of the spec is that neither the OS nor the driver
> has to deal with link training and the link should train to the
> highest speed supported by both ends.  For example, PCIe r4.0, sec 1.2
> says
> 
>    Initialization – During hardware initialization, each PCI Express
>    Link is set up following a negotiation of Lane widths and frequency
>    of operation by the two agents at each end of the Link. No firmware
>    or operating system software is involved.
> 
> Maybe the Intel guys can comment on why HFI needs this code.
> Presumably they didn't write it just for fun, so I assume there's
> some reason.

Yeah there was a reason. It just escapes me what it was right now. Let 
me find out and I'll update.

-Denny