linux-kernel - Re: [PATCH v7 3/4] Bluetooth: hci_qca: Disable IBS state machine and flush Tx buffer

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Date:   Fri, 28 Dec 2018 12:25:20 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v7 3/4] Bluetooth: hci_qca: Disable IBS state machine and
 flush Tx buffer

On Fri, Dec 28, 2018 at 05:18:18PM +0530, Balakrishna Godavarthi wrote:
> During hci down we observed IBS sleep commands are queued in the Tx
> buffer and hci_uart_write_work is sending data to the chip which is
> not required as the chip is powered off. This patch will disable IBS
> and flush the Tx buffer before we turn off the chip.
> 
> Signed-off-by: Balakrishna Godavarthi <bgodavar@...eaurora.org>
> ---
>  drivers/bluetooth/hci_qca.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index b79ef901ab8b..9d5e41f159c7 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -1274,6 +1274,14 @@ static const struct qca_vreg_data qca_soc_data = {
>  
>  static void qca_power_shutdown(struct hci_uart *hu)
>  {
> +	struct qca_data *qca = hu->priv;
> +
> +	/* From this point we go into power off state. But serial port is
> +	 * still open, stop queueing the IBS data and flush all the buffered
> +	 * data in skb's.
> +	 */
> +	clear_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags);

With that you ensure that no IBS wakeup command is sent for the power
pulse, however there could still be a wakeup work in the workqueue
(added before clearing the above bit). If you want to make sure no
IBS wakeup command is pending I think you need to add:

if (work_pending(&qca->ws_awake_device))
	cancel_work_sync(&qca->ws_awake_device);

it's not exactly the case you intend to address with this patch, but a
related (probably less frequent) scenario.