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

[Matthias Kaehlcke <mka@chromium.org>]

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@codeaurora.org>
> ---
> 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'.

> +			   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.

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.

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