linux-kernel - Re: [PATCH 1/3] mwifiex: disable ps_mode explicitly by default instead

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Date:   Fri, 27 Nov 2020 04:44:24 +0900
From:   Tsuchiya Yuto <kitakar@...il.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     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>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...el.com>, verdre@...d.nl
Subject: Re: [PATCH 1/3] mwifiex: disable ps_mode explicitly by default
 instead

On Fri, 2020-11-20 at 13:04 -0800, Brian Norris wrote:
> On Fri, Oct 30, 2020 at 1:04 AM Tsuchiya Yuto <kitakar@...il.com> wrote:
> > On Thu, 2020-10-29 at 11:25 -0700, Brian Norris wrote:
> > > For the record, Chrome OS supports plenty of mwifiex systems with 8897
> > > (SDIO only) and 8997 (PCIe), with PS enabled, and you're hurting
> > > those. Your problem sounds to be exclusively a problem with the PCIe
> > > 8897 firmware.
> > 
> > Actually, I already know that some Chromebooks use these mwifiex cards
> > (but not out PCIe-88W8897) because I personally like chromiumos. I'm
> > always wondering what is the difference. If the difference is firmware,
> > our PCIe-88W8897 firmware should really be fixed instead of this stupid
> > series.
> 
> PCIe is a very different beast. (For one, it uses DMA and
> memory-mapped registers, where SDIO has neither.) It was a very
> difficult slog to get PCIe/8997 working reliably for the few
> Chromebooks that shipped it, and lots of that work is in firmware. I
> would not be surprised if the PCIe-related changes Marvell made for
> 8997 never fed back into their PCIe-8897 firmware. Or maybe they only
> ever launched PCIe-8897 for Windows, and the Windows driver included
> workarounds that were never published to their Linux driver. But now
> I'm just speculating.

Thanks. Yeah, this is indeed hard work. Actually, I (and maybe also other
users) am already thankful that there is wifi driver/firmware available
on Linux :) and it'll be greater if we can fix ps_mode-related issues.

> > Yes, I'm sorry that I know this series is just a stupid one but I have to
> > send this anyway because this stability issue has not been fixed for a
> > long time. I should have added this buglink to every commit as well:
> > 
> > BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=109681
> > 
> > If the firmware can't be fixed, I'm afraid I have to go this way. It makes
> > no sense to keep enabling power_save for the affected devices if we know
> > it's broken.
> 
> Condolences and sympathy, seriously. You likely have little chance of
> getting the firmware fixed, so without new information (e.g,. other
> workarounds?), this is the probably the right way to go.

Thank you for the pointer!

There are two issues regarding ps_mode:
1) fw crashes with "Firmware wakeup failed"
   (I haven't mentioned in this series, but ps_mode also causes fw crashes)
2) connection instability (like large ping delay or even ping not reaching)

If anyone is ever interested in dmesg log with debug_mask=0xffffffff and
device_dump, I posted them to the Bugzilla [1] before.

Regarding the #2, although this is even not a workaround but I found
scanning APs will fix this. So, when I encounter this issue, I keep
scanning APs like "watch -n10 sudo iw dev ${dev_name} scan". So, it
seems that scanning APs will somehow wake wifi up? In other words, wifi
is sleeping when it shouldn't? or wifi somehow failed to wake up when
it should?

Regarding #1, we don't have any ideas yet. There is a guess that memory
leak will occur in the fw every time wifi goes into sleep, but don't know.

We even don't have the exact reproducers for both #1 and #2. What we
know so far is that, enabling ps_mode causes these issues.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=109681#c130

> Brian