linux-kernel - Re: [PATCH v5 1/5] Bluetooth: hci_qca: use wait_until

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Message-ID: <20181222015947.GF261387@google.com>
Date:   Fri, 21 Dec 2018 17:59:47 -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 v5 1/5] Bluetooth: hci_qca: use wait_until_sent() for
 power pulses

On Thu, Dec 20, 2018 at 08:16:35PM +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 | 38 ++++++++++++++-----------------------
>  1 file changed, 14 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index f036c8f98ea3..5a07c2370289 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 +1027,16 @@ 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;
> -
> +	bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", 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",
> +			   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);

serdev_device_wait_until_sent() might only guarantee that the UART
circular buffer is empty (see
https://elixir.bootlin.com/linux/v4.19/source/drivers/tty/tty_ioctl.c#L225),
not that the data has actually sent (e.g. it might be sitting in
the UART FIFO). However with this:

>  	/* Wait for 100 uS for SoC to settle down */
>  	usleep_range(100, 200);

we should probably be fine, unless there's tons of data in the
FIFO.

You currently call serdev_device_write_flush() in
qca_power_shutdown(), I wonder if it would make sense to call it in
qca_send_power_pulse(), regardless of whether it's an on or off
pulse. In any case we don't care if the chip receives any 'pending'
data when we switch it on or off, right?

Cheers

Matthias