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

[Balakrishna Godavarthi]

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@xxxxxxxxxxxxxx>
> > ---
> > 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.