Re: QCA6174 pcie wifi: Add pci quirks

[Ingmar Klein]

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.

Best regards,
Ingmar


Am 15.04.2021 um 04:36 schrieb Alex Williamson:
> On Wed, 14 Apr 2021 16:03:50 -0500
> Bjorn Helgaas <helgaas@xxxxxxxxxx> 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