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Date:   Thu, 15 Apr 2021 13:01:19 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     Ingmar Klein <ingmar_klein@web.de>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, bhelgaas@google.com,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Pali =?UTF-8?B?Um9ow6Fy?= <pali@kernel.org>
Subject: Re: QCA6174 pcie wifi: Add pci quirks
Message-ID: <20210415130119.42bf5b8a@redhat.com>
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[cc +Pali]

On Thu, 15 Apr 2021 20:02:23 +0200
Ingmar Klein <ingmar_klein@web.de> wrote:

> First thanks to you both, Alex and Bjorn!
> I am in no way an expert on this topic, so I have to fully rely on your
> feedback, concerning this issue.
> 
> If you should have any other solution approach, in form of patch-set, I
> would be glad to test it out. Just let me know, what you think might
> make sense.
> I will wait for your further feedback on the issue. In the meantime I
> have my current workaround via quirk entry.
> 
> By the way, my layman's question:
> Do you think, that the following topic might also apply for the QCA6174?
> https://www.spinics.net/lists/linux-pci/msg106395.html
> Or in other words, should a similar approach be tried for the QCA6174
> and if yes, would it bring any benefit at all?
> I hope you can excuse me, in case the questions should not make too much
> sense.

If you run lspci -vvv on your device, what do LnkCap and LnkSta report
under the express capability?  I wonder if your device even supports
>Gen1 speeds, mine does not.

I would not expect that patch to be relevant to you based on your
report.  I understand it to resolve an issue during link retraining to a
higher speed on boot, not during a bus reset.  Pali can correct if I'm
wrong.  Thanks,

Alex

> Am 15.04.2021 um 04:36 schrieb Alex Williamson:
> > On Wed, 14 Apr 2021 16:03:50 -0500
> > Bjorn Helgaas <helgaas@kernel.org> wrote:
> >  
> >> [+cc Alex]
> >>
> >> On Fri, Apr 09, 2021 at 11:26:33AM +0200, Ingmar Klein wrote:  
> >>> Edit: Retry, as I did not consider, that my mail-client would make this
> >>> party html.
> >>>
> >>> Dear maintainers,
> >>> I recently encountered an issue on my Proxmox server system, that
> >>> includes a Qualcomm QCA6174 m.2 PCIe wifi module.
> >>> https://deviwiki.com/wiki/AIRETOS_AFX-QCA6174-NX
> >>>
> >>> On system boot and subsequent virtual machine start (with passed-through
> >>> QCA6174), the VM would just freeze/hang, at the point where the ath10k
> >>> driver loads.
> >>> Quick search in the proxmox related topics, brought me to the following
> >>> discussion, which suggested a PCI quirk entry for the QCA6174 in the kernel:
> >>> https://forum.proxmox.com/threads/pcie-passthrough-freezes-proxmox.27513/
> >>>
> >>> I then went ahead, got the Proxmox kernel source (v5.4.106) and applied
> >>> the attached patch.
> >>> Effect was as hoped, that the VM hangs are now gone. System boots and
> >>> runs as intended.
> >>>
> >>> Judging by the existing quirk entries for Atheros, I would think, that
> >>> my proposed "fix" could be included in the vanilla kernel.
> >>> As far as I saw, there is no entry yet, even in the latest kernel sources.  
> >> This would need a signed-off-by; see
> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=v5.11#n361
> >>
> >> This is an old issue, and likely we'll end up just applying this as
> >> yet another quirk.  But looking at c3e59ee4e766 ("PCI: Mark Atheros
> >> AR93xx to avoid bus reset"), where it started, it seems to be
> >> connected to 425c1b223dac ("PCI: Add Virtual Channel to save/restore
> >> support").
> >>
> >> I'd like to dig into that a bit more to see if there are any clues.
> >> AFAIK Linux itself still doesn't use VC at all, and 425c1b223dac added
> >> a fair bit of code.  I wonder if we're restoring something out of
> >> order or making some simple mistake in the way to restore VC config.  
> > I don't really have any faith in that bisect report in commit
> > c3e59ee4e766.  To double check I dug out the card from that commit,
> > installed an old Fedora release so I could build kernel v3.13,
> > pre-dating 425c1b223dac and tested triggering a bus reset both via
> > setpci and by masking PM reset so that sysfs can trigger the bus reset
> > path with the kernel save/restore code.  Both result in the system
> > hanging when the device is accessed either restoring from the kernel
> > bus reset or reading from the device after the setpci reset.  Thanks,
> >
> > Alex
> >  
>