Re: [PATCH] mwifiex: Add quirk resetting the PCI bridge on MS Surface devices

Jonas Dreßler [off-list ref] wrote:

The most recent firmware (15.68.19.p21) of the 88W8897 PCIe+USB card
reports a hardcoded LTR value to the system during initialization,
probably as an (unsuccessful) attempt of the developers to fix firmware
crashes. This LTR value prevents most of the Microsoft Surface devices
from entering deep powersaving states (either platform C-State 10 or
S0ix state), because the exit latency of that state would be higher than
what the card can tolerate.

Turns out the card works just the same (including the firmware crashes)
no matter if that hardcoded LTR value is reported or not, so it's kind
of useless and only prevents us from saving power.

To get rid of those hardcoded LTR requirements, it's possible to reset
the PCI bridge device after initializing the cards firmware. I'm not
exactly sure why that works, maybe the power management subsystem of the
PCH resets its stored LTR values when doing a function level reset of
the bridge device. Doing the reset once after starting the wifi firmware
works very well, probably because the firmware only reports that LTR
value a single time during firmware startup.

Signed-off-by: Jonas Dreßler <redacted>

I'm not sure what was the conclusion from the discussion, so dropping
the patch. Please resend once it's ready to be applied.

Patch set to Changes Requested.

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20211011134238.16551-1-verdre@v0yd.nl/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches