linux-kernel - Re: [PATCH RFC v2 4/4] PCI: hotplug: Add quirk For Dell nvme pcie switches

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Message-ID: <CAOSf1CGqKePUE7Z9R3ojX6Ba_RxsdS7Y2rHONzbZNPNti8MtwQ@mail.gmail.com>
Date:   Fri, 22 Feb 2019 13:04:51 +1100
From:   Oliver <oohall@...il.com>
To:     Alex_Gagniuc@...lteam.com
Cc:     Lukas Wunner <lukas@...ner.de>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Austin.Bolen@...l.com,
        Keith Busch <keith.busch@...el.com>, Shyam.Iyer@...l.com,
        okaya@...nel.org, linux-pci@...r.kernel.org,
        mika.westerberg@...ux.intel.com, Sinan Kaya <okaya@...eaurora.org>,
        poza@...eaurora.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 4/4] PCI: hotplug: Add quirk For Dell nvme pcie switches

On Fri, Feb 22, 2019 at 5:38 AM <Alex_Gagniuc@...lteam.com> wrote:
>
> On 2/21/19 1:57 AM, Lukas Wunner wrote:
> >
> > [EXTERNAL EMAIL]
> >
> > On Tue, Feb 19, 2019 at 07:20:30PM -0600, Alexandru Gagniuc wrote:
> >> --- a/drivers/pci/hotplug/pciehp_hpc.c
> >> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> >> @@ -952,3 +952,23 @@ DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_QCOM, 0x0400,
> >>                            PCI_CLASS_BRIDGE_PCI, 8, quirk_cmd_compl);
> >>   DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_QCOM, 0x0401,
> >>                            PCI_CLASS_BRIDGE_PCI, 8, quirk_cmd_compl);
> >> +
> >> +
> >
> > Duplicate newline.
> >
> >
> >> +static void fixup_dell_nvme_backplane_switches(struct pci_dev *pdev)
> >
> > Can we have a little code comment above the function such as:
> >
> > +/*
> > + * Dell <product name> NVMe storage backplanes disable in-band presence
> > + * (PCIe r5.0 sec X.Y.Z) but neglect to set the corresponding flag in the
> > + * Slot Capabilities 2 register.
> > + */
> >
> >
> >> +    if (pdev->subsystem_vendor != PCI_VENDOR_ID_DELL
> >> +            || pdev->subsystem_device != 0x1fc7)
> >
> > This looks a little unpolished, how about:
> >
> > +     if (pdev->subsystem_vendor != PCI_VENDOR_ID_DELL ||
> > +         pdev->subsystem_device != 0x1fc7)
> >
> >
> >> +            return;
> >> +
> >> +    pdev->no_in_band_presence = 1;
> >> +}
> >> +
> >> +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_PLX, 0x9733,
> >
> > By convention there's no blank line between the closing curly brace
> > and the DECLARE_PCI_FIXUP_CLASS_FINAL().
>
> I'm sorry for all the style issues. I realize it's noise and should just
> be done right from the beginning. Is there a way to make checkpatch.pl
> catch these before they go out?
>
>
> > If the quirk is x86-specific, please enclose it in "#ifdef CONFIG_X86"
> > to reduce kernel footprint on other arches.
>
> That's a tricky one. If you look at p. 185 of [1], items 9, 11, and 12
> are standard x16 cards that would fit in any x16 slot. Those cards have
> the offending switches.
>
> On the one hand, you could take the cards and backplane and put them in
> a non-hax86 system. On the other hand, I don't see why someone would
> want to do this.

I have a couple of POWER boxes with Dell branded switch cards in them.
I have no idea why either, but it does happen.

>
> Alex
>
> [1] https://topics-cdn.dell.com/pdf/poweredge-r740xd_owners-manual_en-us.pdf
>
>