linux-kernel - Re: [PATCH v9 3/3] Bluetooth: hci_qca: Disable IBS state machine and flush Tx buffer

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Date:   Fri, 01 Feb 2019 17:10:11 +0530
From:   Balakrishna Godavarthi <bgodavar@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com, johan@...nel.org,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v9 3/3] Bluetooth: hci_qca: Disable IBS state machine and
 flush Tx buffer

Hi Matthias,

On 2019-01-25 06:25, Matthias Kaehlcke wrote:
> On Thu, Jan 24, 2019 at 05:38:08PM +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>
>> ---
>> Changes v9:
>>   * added lock while disabling the IBS state machine.
>> 
>> ---
>>  drivers/bluetooth/hci_qca.c | 17 +++++++++++++++--
>>  1 file changed, 15 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
>> index 6b5bcd44e24c..99ddc35f08c6 100644
>> --- a/drivers/bluetooth/hci_qca.c
>> +++ b/drivers/bluetooth/hci_qca.c
>> @@ -771,16 +771,17 @@ static int qca_enqueue(struct hci_uart *hu, 
>> struct sk_buff *skb)
>>  	/* Prepend skb with frame type */
>>  	memcpy(skb_push(skb, 1), &hci_skb_pkt_type(skb), 1);
>> 
>> +	spin_lock_irqsave(&qca->hci_ibs_lock, flags);
>> +
>>  	/* Don't go to sleep in middle of patch download or
>>  	 * Out-Of-Band(GPIOs control) sleep is selected.
>>  	 */
>>  	if (!test_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags)) {
>>  		skb_queue_tail(&qca->txq, skb);
>> +		spin_unlock_irqrestore(&qca->hci_ibs_lock, flags);
>>  		return 0;
>>  	}
>> 
>> -	spin_lock_irqsave(&qca->hci_ibs_lock, flags);
>> -
>>  	/* Act according to current state */
>>  	switch (qca->tx_ibs_state) {
>>  	case HCI_IBS_TX_AWAKE:
>> @@ -1273,6 +1274,18 @@ static const struct qca_vreg_data qca_soc_data 
>> = {
>> 
>>  static void qca_power_shutdown(struct hci_uart *hu)
>>  {
>> +	struct qca_data *qca = hu->priv;
>> +	unsigned long flags;
>> +
>> +	/* 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.
>> +	 */
>> +	spin_lock_irqsave(&qca->hci_ibs_lock, flags);
>> +	clear_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags);
>> +	qca_flush(hu);
>> +	spin_unlock_irqrestore(&qca->hci_ibs_lock, flags);
>> +
>>  	host_set_baudrate(hu, 2400);
>>  	qca_send_power_pulse(hu, QCA_WCN3990_POWEROFF_PULSE);
>>  	qca_power_setup(hu, false);
> 
> I was about to add my 'Reviewed-by' tag, but I'm still left with a
> doubt. This patch certainly improves the situation by clearing the IBS
> bit and flushing the buffered data, however IIUC new data could still
> be added to the TX queue after releasing the spinlock:
> 
> static int qca_enqueue(struct hci_uart *hu, struct sk_buff *skb)
> {
> 	...
> 
> 	if (!test_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags)) {
> 		skb_queue_tail(&qca->txq, skb);
> 
> 	...
> }
> 
> To prevent this a boolean/bit like 'shutting_down' or similar would be
> needed (I don't think there is something common in the HCI core),
> which is set in qca_power_shutdown(). If the bit is set qca_enqueue()
> discards the data.
> 
> Not sure how important this is, and I don't want to add necessarily
> more revisions to this series. If it is preferable to have an empty
> queue after shutdown maybe it can be done in a follow up patch.
> 
> Thanks
> 
> Matthias

[Bala]: during shutdown Bt stack will not send any data to the Bt  
kernel Tx path.
         so this call may not be called. once we shutdown chip.

-- 
Regards
Balakrishna.