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

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Message-ID: <20190201183506.GR81583@google.com>
Date:   Fri, 1 Feb 2019 10:35:06 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.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

On Fri, Feb 01, 2019 at 05:10:11PM +0530, Balakrishna Godavarthi wrote:
> 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.

Thanks for the clarification! I kinda expected that, but it wasn't
evident to me from the core code.

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>