Message-ID: <20210528182135.e7uiugoyuj7hjilb@pali>
Date:   Fri, 28 May 2021 20:21:35 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Ingmar Klein <ingmar_klein@....de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: QCA6174 pcie wifi: Add pci quirks

Hello Ingmar!

Now I see that in your patch you have Atheros card with id 0x003e:
https://lore.kernel.org/linux-pci/08982e05-b6e8-5a8d-24ab-da1488ee50a8@web.de/

With my patch I have tested 5 different Atheros cards but none has id 0x003e:
https://lore.kernel.org/linux-pci/20210505163357.16012-1-pali@kernel.org/

So my patch does not fix that issue for your 0x003e card. I just do not
have such card for testing.

Could you try to apply my patch and then add your id 0x003e into quirk
list if it helps?

On Friday 28 May 2021 20:08:52 Ingmar Klein wrote:
> Thanks to both of you, Bjorn and Pali!
> I had hoped that Pali would come with an appropriate fix. Good to know,
> that this is taken care of.
> 
> Will test ASAP, but I am confident, that it will work anyway.
> Should it unexpectedly not fix my issues, I'll let you know.
> Have a nice weekend!
> Best regards,
> Ingmar
> 
> 
> Am 26.05.2021 um 00:12 schrieb Bjorn Helgaas:
> > On Thu, Apr 15, 2021 at 09:53:38PM +0200, Pali Rohár wrote:
> > > Hello!
> > > 
> > > On Thursday 15 April 2021 13:01:19 Alex Williamson wrote:
> > > > [cc +Pali]
> > > > 
> > > > On Thu, 15 Apr 2021 20:02:23 +0200
> > > > Ingmar Klein <ingmar_klein@....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
> > > I have been testing more ath cards and I'm going to send a new version
> > > of this patch with including more PCI ids.
> > Dropping this patch in favor of Pali's new version.
> > 
> > > > > 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,
> > > These two issues are are related. Both operations (PCIe Hot Reset and
> > > PCIe Link Retraining) cause reset of ath chips. Seems that they cause
> > > double reset. After reset these chips reads configuration from internal
> > > EEPROM/OTP and if another reset is triggered prior chip finishes
> > > internal configuration read then it stops working. My testing showed
> > > that ath10k chips completely disappear from the PCIe bus, some ath9k
> > > chips works fine but starts reporting incorrect PCI ID (0xABCD) and some
> > > other ath9k chips reports correct PCI ID but does not work. I had
> > > discussion with Adrian Chadd who knows probably everything about ath9k
> > > and confirmed me that this issue is there with ath9k and ath10k chips.
> > > 
> > > He wrote me that workaround to turn card back from this "broken" state
> > > is to do PCIe Cold Reset of the card, which means turning power supply
> > > off for particular PCIe slot. Such thing is not supported on many
> > > low-end boards, so workaround cannot be applied.
> > > 
> > > I was able to recover my testing cards from this "broken" state by PCIe
> > > Warm Reset (= reset via PERST# pin).
> > > 
> > > I have tried many other reset methods (PCIe PM reset, Link Down, PCIe
> > > Hot Reset with bigger internal, ...) but nothing worked. So seems that
> > > the only workaround is to do PCIe Cold Reset or PCIe Warm Reset.
> > > 
> > > I will send V2 of my patch with details and explanation.
> > > 
> > > As kernel does not have API for doing PCIe Warm Reset, I think is
> > > another argument why kernel really needs it.
> > > 
> > > I do not have any QCA6174 card for testing, but based on the fact I
> > > reproduced this issue with more ath9k and ath10 cards and Adrian
> > > confirmed that above reset issue is there, I think that it affects all
> > > AR9xxx and QCAxxxx cards handled by ath9k and ath10 drivers.
> > > 
> > > I was told that AMI BIOS was patching their BIOSes found in notebooks to
> > > avoid triggering this issue on notebooks ath9k cards.
> > > 
> > > > Alex
> > > > 
> > > > > Am 15.04.2021 um 04:36 schrieb Alex Williamson:
> > > > > > On Wed, 14 Apr 2021 16:03:50 -0500
> > > > > > Bjorn Helgaas <helgaas@...nel.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
> > > > > > 

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