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

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Date:   Mon, 18 Oct 2021 12:27:24 +0000 (UTC)
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Jonas Dreßler <verdre@...d.nl>
Cc:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Xinming Hu <huxinming820@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonas Dreßler <verdre@...d.nl>,
        Tsuchiya Yuto <kitakar@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Maximilian Luz <luzmaximilian@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Pali Rohár <pali@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        Brian Norris <briannorris@...omium.org>,
        David Laight <David.Laight@...LAB.COM>
Subject: Re: [PATCH] mwifiex: Add quirk resetting the PCI bridge on MS Surface
 devices

Jonas Dreßler <verdre@...d.nl> 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 <verdre@...d.nl>

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