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@xxxxxx> 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@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 > > > > > > > > >
