Date:   Fri, 9 Jul 2021 19:30:13 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     Jonas Dreßler <verdre@...d.nl>,
        Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi.bhat@....com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Tsuchiya Yuto <kitakar@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2 2/2] mwifiex: pcie: add reset_d3cold quirk for Surface
 gen4+ devices

On Friday 09 July 2021 19:03:37 Maximilian Luz wrote:
> On 7/9/21 6:12 PM, Pali Rohár wrote:
> 
> [...]
> 
> > > > Hello! Now I'm thinking loudly about this patch. Why this kind of reset
> > > > is needed only for Surface devices? AFAIK these 88W8897 chips are same
> > > > in all cards. Chip itself implements PCIe interface (and also SDIO) so
> > > > for me looks very strange if this 88W8897 PCIe device needs DMI specific
> > > > quirks. I cannot believe that Microsoft got some special version of
> > > > these chips from Marvell which are different than version uses on cards
> > > > in mPCIe form factor.
> > > > 
> > > > And now when I'm reading comment below about PCIe bridge to which is
> > > > this 88W8897 PCIe chip connected, is not this rather an issue in that
> > > > PCIe bridge (instead of mwifiex/88W8897) or in ACPI firmware which
> > > > controls this bridge?
> > > > 
> > > > Or are having other people same issues on mPCIe form factor wifi cards
> > > > with 88W8897 chips and then this quirk should not DMI dependent?
> > > > 
> > > > Note that I'm seeing issues with reset and other things also on chip
> > > > 88W8997 when is connected to system via SDIO. These chips have both PCIe
> > > > and SDIO buses, it just depends which pins are used.
> > > > 
> > > 
> > > Hi and thanks for the quick reply! Honestly I've no idea, this is just the
> > > first method we found that allows for a proper reset of the chip. What I
> > > know is that some Surface devices need that ACPI DSM call (the one that was
> > > done in the commit I dropped in this version of the patchset) to reset the
> > > chip instead of this method.
> > > 
> > > Afaik other devices with this chip don't need this resetting method, at
> > > least Marvell employees couldn't reproduce the issues on their testing
> > > devices.
> > > 
> > > So would you suggest we just try to match for the pci chip 88W8897 instead?
> > 
> > Hello! Such suggestion makes sense when we know that it is 88W8897
> > issue. But if you got information that issue cannot be reproduced on
> > other 88W8897 cards then matching 88W8897 is not correct.
> > 
> >  From all this information looks like that it is problem in (Microsoft?)
> > PCIe bridge to which is card connected. Otherwise I do not reason how it
> > can be 88W8897 affected. Either it is reproducible on 88W8897 cards also
> > in other devices or issue is not on 88W8897 card.
> 
> I doubt that it's an issue with the PCIe bridge (itself at least). The
> same type of bridge is used for both dGPU and NVME SSD on my device (see
> lspci output below) and those work fine. Also if I'm seeing that right
> it's from the Intel CPU, so my guess is that a lot more people would
> have issues with that then.

>From information below it seems to be related to surprise removal.
Therefore is surprise removal working without issue for dGPU or NVME
SSD? Not all PCIe bridges support surprise removal...

> 
> I don't know about the hardware side, so it might be possible that it's
> an issue with integrating both bridge and wifi chip, in which case it's
> still probably best handled via DMI quirks unless we know more.
> 
> Also as Tsuchiya mentioned in his original submission, on Windows the
> device is reset via this D3cold method. I've only skimmed that
> errata.inf file mentioned, but I think this is what he's referring to:
> 
>   Controls whether ACPIDeviceEnableD3ColdOnSurpriseRemoval rule will be
>   evaluated or not on a given platform. Currently
>   ACPIDeviceEnableD3ColdOnSurpriseRemoval rule only needs to be
>   evaluated on Surface platforms which contain the Marvell WiFi
>   controller which depends on device going through D3Cold as part of
>   surprise-removal.
> 
> and
> 
>   Starting with Windows releases *after* Blue, ACPI will not put
>   surprise-removed devices into D3Cold automatically. Some known
>   scenarios (viz. WiFi reset/recovery) rely on the device cycling
>   through D3Cold on surprise-removal. This hack allows surprise-removed
>   devices to be put into D3Cold (if supported by the stack).
> 
> So, as far as I can tell, the chip doesn't like to be surprise-removed
> (which seems to happen during reset) and then needs to be power-cycled,
> which I think is likely due to some issue with firmware state.

Thanks for information. This really does not look like PCIe bridge
specific if bridge itself can handle surprise-removed devices. lspci can
tell us if bridge supports it or not (see below).

> So the quirk on Windows seems very Surface specific.
> 
> There also seem a bunch of revisions of these chips around, for example
> my SB2 is affected by a bug that we've tied to the specific hardware
> revision which causes some issues with host-sleep (IIRC chip switches
> rapidly between wake and sleep states without any external influence,
> which is not how it should behave and how it does behave on a later
> hardware revision).

Interesting... This looks like the issue can be in 88W8897 chip and
needs some special conditions to trigger? And Surface is triggering it
always?

> > > Then we'd probably have to check if there are any laptops where multiple
> > > devices are connected to the pci bridge as Amey suggested in a review
> > > before.
> > 
> > Well, I do not know... But if this is issue with PCIe bridge then
> > similar issue could be observed also for other PCIe devices with this
> > PCIe bridge. But question is if there are other laptops with this PCIe
> > bridge. And also it can be a problem in ACPI firmware on those Surface
> > devices, which implements some PCIe bridge functionality. So it is
> > possible that issue is with PCIe bridge, not in HW, but in SW/firmware
> > part which can be Microsoft specific... So too many questions to which
> > we do not know answers.
> > 
> > Could you provide output of 'lspci -nn -vv' and 'lspci -tvnn' on
> > affected machines? If you have already sent it in some previous email,
> > just send a link. At least I'm not able to find it right now and output
> > may contain something useful...
> 
> From my Surface Book 2 (with the same issue):
> 
>  - lspci -tvnn: https://paste.ubuntu.com/p/mm3YpcZJ8N/
>  - lspci -vv -nn: https://paste.ubuntu.com/p/dctTDP738N/

Could you re-run lspci under root account? There are missing important
parts like "Capabilities: <access denied>" where is information if
bridge supports surprise removal or not.

> Regards,
> Max

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