Re: [PATCH v2 2/2] mwifiex: pcie: add reset_d3cold quirk for Surface gen4+ devices

From: Jonas Dreßler
Date: Sun Jul 11 2021 - 12:31:29 EST

On 7/9/21 7:30 PM, Pali Rohár wrote:
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

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


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

The specific issue was that the card wakes up very quickly after going into deep sleep (deep sleep is a state the firmware enters when idle and not connected to an AP). Now this in turn messed with the host suspending, because deep sleep is involved there and the card is not expected to wake up that quickly again (I'm oversimplifying here, it's also been some time since we looked into it).

Anyway, in the end those wakeups from deep sleep only happened with one hardware revision of the card (I guess it's caused by a hardware design issue like a floating gpio or something), and we managed to fix the problems by disabling deep sleep on that hardware revision, but as Max mentioned that problem is completely unrelated from this patch.

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

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:
- lspci -vv -nn:

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.