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Message-ID: <5f0b52be-8b9c-b015-6c5a-f2f470e37058@v0yd.nl>
Date: Sun, 3 Oct 2021 11:18:15 +0200
From: Jonas Dreßler <verdre@...d.nl>
To: Amitkumar Karwar <amitkarwar@...il.com>,
Ganapathi Bhat <ganapathi017@...il.com>,
Xinming Hu <huxinming820@...il.com>,
Kalle Valo <kvalo@...eaurora.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Cc: 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>, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mwifiex: Try waking the firmware until we get an
interrupt
On 9/14/21 13:48, Jonas Dreßler wrote:
> It seems that the firmware 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 (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 didn't send us 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.
>
> A good reproducer for this issue is letting the firmware sleep and wake
> up in very short intervals, for example by pinging a device on the
> network every 0.1 seconds.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Jonas Dreßler <verdre@...d.nl>
> ---
> drivers/net/wireless/marvell/mwifiex/pcie.c | 33 +++++++++++++++++----
> 1 file changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c b/drivers/net/wireless/marvell/mwifiex/pcie.c
> index 0eff717ac5fa..7fea319e013c 100644
> --- a/drivers/net/wireless/marvell/mwifiex/pcie.c
> +++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
> @@ -661,11 +661,15 @@ static void mwifiex_delay_for_sleep_cookie(struct mwifiex_adapter *adapter,
> "max count reached while accessing sleep cookie\n");
> }
>
> +#define N_WAKEUP_TRIES_SHORT_INTERVAL 15
> +#define N_WAKEUP_TRIES_LONG_INTERVAL 35
> +
> /* This function wakes up the card by reading fw_status register. */
> static int mwifiex_pm_wakeup_card(struct mwifiex_adapter *adapter)
> {
> struct pcie_service_card *card = adapter->card;
> const struct mwifiex_pcie_card_reg *reg = card->pcie.reg;
> + int n_tries = 0;
>
> mwifiex_dbg(adapter, EVENT,
> "event: Wakeup device...\n");
> @@ -673,12 +677,29 @@ static int mwifiex_pm_wakeup_card(struct mwifiex_adapter *adapter)
> if (reg->sleep_cookie)
> mwifiex_pcie_dev_wakeup_delay(adapter);
>
> - /* Accessing fw_status register will wakeup device */
> - if (mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE)) {
> - mwifiex_dbg(adapter, ERROR,
> - "Writing fw_status register failed\n");
> - return -1;
> - }
> + /* 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 -EIO;
> + }
> +
> + n_tries++;
> +
> + if (n_tries <= N_WAKEUP_TRIES_SHORT_INTERVAL)
> + usleep_range(400, 700);
> + else
> + msleep(10);
> + } while (n_tries <= N_WAKEUP_TRIES_SHORT_INTERVAL + N_WAKEUP_TRIES_LONG_INTERVAL &&
> + READ_ONCE(adapter->int_status) == 0);
> +
> + mwifiex_dbg(adapter, EVENT,
> + "event: Tried %d times until firmware woke up\n", n_tries);
>
> if (reg->sleep_cookie) {
> mwifiex_pcie_dev_wakeup_delay(adapter);
>
So I think I have another solution that might be a lot more elegant, how
about this:
try_again:
n_tries++;
mwifiex_write_reg(adapter, reg->fw_status, FIRMWARE_READY_PCIE);
if (wait_event_interruptible_timeout(adapter->card_wakeup_wait_q,
READ_ONCE(adapter->int_status) != 0,
WAKEUP_TRY_AGAIN_TIMEOUT) == 0 &&
n_tries < MAX_N_WAKEUP_TRIES) {
goto try_again;
}
and then call wake_up_interruptible() in the mwifiex_interrupt_status()
interrupt handler.
This solution should make sure we always keep wakeup latency to a minimum
and can still retry the register write if things didn't work.
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