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From:   Rajat Jain <rajatja@google.com>
Date:   Tue, 21 Aug 2018 13:24:22 -0700
Message-ID: <CACK8Z6FTy8CyYbuaOu1Fucty1AMYRmsKQAXFJJhELq-qt5cb9A@mail.gmail.com>
Subject: Re: Enumeration issue with QCA9005 AR9462
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Lukas Wunner <lukas@wunner.de>,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        mmyangfl@gmail.com, ashok.raj@intel.com
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On Tue, Aug 21, 2018 at 9:50 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> [+cc Rajat, Ashok]
>
> On Tue, Aug 21, 2018 at 09:25:41AM +0200, Lukas Wunner wrote:
> > On Tue, Aug 21, 2018 at 07:47:04AM +0200, Lukas Wunner wrote:
> > > On Mon, Aug 20, 2018 at 06:06:24PM -0500, Bjorn Helgaas wrote:
> > > > mmyangfl@gmail.com reported a problem [1]: on v4.17, a QCA9005 AR9462
> > > > wifi device was present at boot, but disappeared after suspend/resume.
> > > >
> > > > He also tested a recent kernel (5c60a7389d79, from Thu Aug 16),
> > > > where the suspend/resume problem doesn't seem to happen, but the wifi
> > > > device isn't enumerated correctly at boot-time.
> > > >
> > > > [    0.928714] pciehp 0000:04:00.0:pcie204: Slot #0 AttnBtn- PwrCtrl- MRL- AttnInd- PwrInd- HotPlug+ Surprise+ Interlock- NoCompl- LLActRep+
> > > > [    0.928752] pciehp 0000:04:00.0:pcie204: Slot(0-1): Card not present
> > > > [    0.928811] pciehp 0000:04:00.0:pcie204: Slot(0-1): Link Up
> > > > [    0.928815] pciehp 0000:04:00.0:pcie204: Slot(0-1): No adapter
> > > >
> > > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=200839
> > > > [2] https://bugzilla.kernel.org/attachment.cgi?id=277923
> > >
> > > The hardware appears to be broken in that the Presence Detect State bit
> > > in the Slot Status register is 0 (Slot Empty) even though the slot is
> > > occupied.
> > [...]
> > > Possible solutions:
> > >
> > > (a) Be lenient towards broken hardware and accept DLActive+ as a proxy
> > >     for PresDet+.
> > >
> > > (b) Add a blacklist to pciehp such that it doesn't bind to [1ae9:0200].
> > >     The bug reporter writes that "it's a single Half Mini PCIe card,
> > >     with two chipsets (Wil6110? + AR9462) combined by a PCIe hub".
> > >     This sounds like it's not really hotpluggable.
> > >     (Is Mini PCIe hotplug capable at all?)
> > >
> > > Let me go through the driver and see if (a) is feasible and how intrusive
> > > it would be.
> >
> > So (a) would seem to be feasible, we could add a quirk for devices like
> > this to call pciehp_check_link_active() in pciehp_get_adapter_status().
> >
> > Alternatively, we could generally add a call to pciehp_check_link_active()
> > in get_adapter_status(), pciehp_check_presence() and pcie_init() and thus
> > avoid a quirk for this specific device.
> > The existing call in __pciehp_enable_slot() could actually be removed,
> > this code path is only entered if either PDS or DLLLA is set.
> >
> > And the third option would be to add a quirk like quirk_hotplug_bridge()
> > which sets is_hotplug_bridge = 0 on this broken device such that pciehp
> > doesn't bind to it in the first place.
>
> It sounds like with (a), you could make this work without having a
> Wil6110-specific quirk, i.e., if the Link Status says the link is
> active, we assume a device is present.  That seems reasonable to me
> and it sort of fits with these previous changes:


I also like idea (a) and think it makes sense. One thing to note is
that we may pass the same confusion ("how is my wifi detected when no
card is not present on the slot") to userspace in case anyone looks in
/sysfs (but I don't think anyone looks that deeply).

Thanks,

Rajat


>
>
>   385895fef6b5 ("PCI: pciehp: Prioritize data-link event over presence detect")
>   e48f1b67f668 ("PCI: pciehp: Use link change notifications for hot-plug and removal")
>
> Bjorn