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It seems that the PCIe+USB firmware (latest version 15.68.19.p21) of the 88W8897 card sometimes ignores or misses when we try to wake it up by writing to the firmware status register. This leads to the firmware wakeup timeout expiring and the driver resetting the card because we assume the firmware has hung up or crashed. Turns out that the firmware actually didn't hang up, but simply "missed" our wakeup request and didn't send us an interrupt with an AWAKE event. Trying again to read the firmware status register after a short timeout usually makes the firmware wake up as expected, so add a small retry loop to mwifiex_pm_wakeup_card() that looks at the interrupt status to check whether the card woke up. The number of tries and timeout lengths for this were determined experimentally: The firmware usually takes about 500 us to wake up after we attempt to read the status register. In some cases where the firmware is very busy (for example while doing a bluetooth scan) it might even miss our requests for multiple milliseconds, which is why after 15 tries the waiting time gets increased to 10 ms. The maximum number of tries it took to wake the firmware when testing this was around 20, so a maximum number of 50 tries should give us plenty of safety margin. Here's a reproducer for those firmware wakeup failures I've found: 1) Make sure wifi powersaving is enabled (iw dev wlp1s0 set power_save on) 2) Connect to any wifi network (makes firmware go into wifi powersaving mode, not deep sleep) 3) Make sure bluetooth is turned off (to ensure the firmware actually enters powersave mode and doesn't keep the radio active doing bluetooth stuff) 4) To confirm that wifi powersaving is entered ping a device on the LAN, pings should be a few ms higher than without powersaving 5) Run "while true; do iwconfig; sleep 0.0001; done", this wakes and suspends the firmware extremely often 6) Wait until things explode, for me it consistently takes <5 minutes BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=109681 Cc: stable@vger.kernel.org Signed-off-by: Jonas Dreßler <verdre@v0yd.nl> Signed-off-by: Kalle Valo <kvalo@codeaurora.org> Link: https://lore.kernel.org/r/20211011133224.15561-3-verdre@v0yd.nl |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.