linux-kernel - Re: [PATCH v1 1/4] Bluetooth: hci_qca: use wait_until

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Date:   Tue, 13 Nov 2018 16:17:17 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v1 1/4] Bluetooth: hci_qca: use wait_until_sent() for
 power pulses

On Tue, Nov 06, 2018 at 05:35:25PM +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@...eaurora.org>
> ---
>  drivers/bluetooth/hci_qca.c | 22 +++++++++-------------
>  1 file changed, 9 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index f72ded4ec9ae..051f081d1835 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -1016,8 +1016,7 @@ static inline void host_set_baudrate(struct hci_uart *hu, unsigned int speed)
>  static int qca_send_power_pulse(struct hci_dev *hdev, 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
> @@ -1030,18 +1029,14 @@ static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
>  	 * 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;
> -
>  	hci_uart_set_flow_control(hu, true);
> +	ret = serdev_device_write(hu->serdev, &cmd, sizeof(cmd), 0);
> +	if (ret < 0) {
> +		bt_dev_err(hdev, "failed to send power pulse %02x to SoC", 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);

Is the delay still needed now that we wait for the pulse to be sent? I
didn't observe any problems without it in a few dozens of iterations.

> @@ -1283,7 +1278,8 @@ static void qca_power_shutdown(struct hci_uart *hu)
>  
>  	host_set_baudrate(hu, 2400);
>  	hci_uart_set_flow_control(hu, true);
> -	serdev_device_write_buf(serdev, &cmd, sizeof(cmd));
> +	serdev_device_write(serdev, &cmd, sizeof(cmd), 0);
> +	serdev_device_wait_until_sent(serdev, 0);
>  	hci_uart_set_flow_control(hu, false);

You could call qca_send_power_pulse(hdev, QCA_WCN3990_POWEROFF_PULSE)
instead, as an earlier patch set did before skbs were used to send the
power pulse.

You can also consider to set the baudrate in qca_send_power_pulse()
depending on the power pulse. On the plus side this would reduce a bit
of clutter in the callers of qca_send_power_pulse(), on the negative
side it would be harder to follow when baudrate changes occur (not
sure this is a problem). Up to you, just an idea.

Thanks

Matthias