Re: [PATCH v6 1/6] Bluetooth: hci_qca: use wait_until_sent() for power pulses

[Balakrishna Godavarthi]

HI Matthias,

On 2018-12-28 01:48, Matthias Kaehlcke wrote:
> On Thu, Dec 27, 2018 at 01:01:31PM +0530, Balakrishna Godavarthi wrote:
> > wcn3990 requires a power pulse to turn ON/OFF along with
> > regulators. Sometimes we are observing the power pulses are sent
> > out with some time delay, due to queuing these commands. This is
> > causing synchronization issues with chip, which intern delay the
> > chip setup or may end up with communication issues.
> >
> > Signed-off-by: Balakrishna Godavarthi <bgodavar@xxxxxxxxxxxxxx>
> > ---
> > Changes in v6:
> >  * added serdev_device_write_flush() in qca_send_power_pulse
> >    instead during the power off pulse.
> >
> > Changes in v5:
> >  * added serdev_device_write_flush() in qca_power_off().
> >
> > ---
> >  drivers/bluetooth/hci_qca.c | 38 
> > ++++++++++++++-----------------------
> >  1 file changed, 14 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index f036c8f98ea3..507a2355c758 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -1013,11 +1013,9 @@ static inline void host_set_baudrate(struct 
> > hci_uart *hu, unsigned int speed)
> >  		hci_uart_set_baudrate(hu, speed);
> >  }
> >
> > -static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
> > +static int qca_send_power_pulse(struct hci_uart *hu, u8 cmd)
> >  {
> > -	struct hci_uart *hu = hci_get_drvdata(hdev);
> > -	struct qca_data *qca = hu->priv;
> > -	struct sk_buff *skb;
> > +	int ret;
> >
> >  	/* These power pulses are single byte command which are sent
> >  	 * at required baudrate to wcn3990. On wcn3990, we have an external
> > @@ -1029,19 +1027,17 @@ static int qca_send_power_pulse(struct hci_dev 
> > *hdev, u8 cmd)
> >  	 * save power. Disabling hardware flow control is mandatory while
> >  	 * sending power pulses to SoC.
> >  	 */
> > -	bt_dev_dbg(hdev, "sending power pulse %02x to SoC", cmd);
> > -
> > -	skb = bt_skb_alloc(sizeof(cmd), GFP_KERNEL);
> > -	if (!skb)
> > -		return -ENOMEM;
> > -
> > +	serdev_device_write_flush(hu->serdev);
> > +	bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
>
> nit: why clutter the code flow by putting the log statement in the
> middle of code that is actually doing something with the serial
> interface?
>
> In case you respin anyway I suggest to structure it like this:
>
>   bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
>
>   hci_uart_set_flow_control(hu, true);
>   serdev_device_write_flush(hu->serdev);
>   ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd));
>
>
> >  	hci_uart_set_flow_control(hu, true);
> > +	ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd));
> > +	if (ret < 0) {
> > +		bt_dev_err(hu->hdev, "failed to send power pulse %02x to SoC",
>
> nit: especially on 'embedded' devices 'SoC' is typically associated
> with the CPU running Linux, you might want to change it to
> 'controller'.

[Bala]: will update.

> > +			   cmd);
> > +		return ret;
> > +	}
> >
> > -	skb_put_u8(skb, cmd);
> > -	hci_skb_pkt_type(skb) = HCI_COMMAND_PKT;
> > -
> > -	skb_queue_tail(&qca->txq, skb);
> > -	hci_uart_tx_wakeup(hu);
> > +	serdev_device_wait_until_sent(hu->serdev, 0);
> >
> >  	/* Wait for 100 uS for SoC to settle down */
> >  	usleep_range(100, 200);
>
> I said earlier the delay here should be enough to ensure that the byte
> gets transferred from a hardware buffer/FIFO to the controller,
> however that didn't take into account that the power pulses are sent
> with a baudrate of 2400. That translates to ~240 bytes/s, hence a
> delay of 5 ms is needed to be on the safe side.

[Bala]: sure will update the delay of 5 ms.

> In case you change the delay please also update the comment to make
> clear this is not only time for the BT controller to settle, but also
> to guarantee that the command was actually sent to the controller.

[Bala]: will update the comment.

> So far it seems no problems have been observed, though this could be
> thanks to the 100 ms delay in qca_wcn3990_init().
>
> Cheers
>
> Matthias

--
Regards
Balakrishna.