Re: [PATCH 2/2] mwifiex: Try waking the firmware until we get an interrupt

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Mon, Aug 30, 2021 at 3:39 PM Jonas Dreßler <verdre@v0yd.nl> wrote:
>
> It seems that the firmware of the 88W8897 card sometimes ignores or
> misses when we try to wake it up by reading 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 (unfortunately that's not unlikely with this card).
>
> Turns out that most of the time the firmware actually didn't hang up,
> but simply "missed" our wakeup request and doesn't send us an AWAKE

didn't

> event.
>
> Trying again to read the firmware status register after a short timeout
> usually makes the firmware wake we up as expected, so add a small retry

wake up

> 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.
>
> A good reproducer for this issue is letting the firmware sleep and wake
> up in very short intervals, for example by pinging an device on the

a device

> network every 0.1 seconds.

...

> +       /* Access the fw_status register to wake up the device.
> +        * Since the 88W8897 firmware sometimes appears to ignore or miss
> +        * that wakeup request, we continue trying until we receive an
> +        * interrupt from the card.
> +        */
> +       do {
> +               if (mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE)) {
> +                       mwifiex_dbg(adapter, ERROR,
> +                                   "Writing fw_status register failed\n");
> +                       return -1;
> +               }
> +
> +               n_tries++;
> +
> +               if (n_tries <= 15)
> +                       usleep_range(400, 700);
> +               else
> +                       msleep(10);
> +       } while (n_tries <= 50 && READ_ONCE(adapter->int_status) == 0);

NIH read_poll_timeout() from iopoll.h.

-- 
With Best Regards,
Andy Shevchenko