linux-kernel - Re: [PATCH v8 1/3] Bluetooth: hci_qca: use wait_until

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Message-ID: <20190116202253.GS261387@google.com>
Date:   Wed, 16 Jan 2019 12:22:53 -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 v8 1/3] Bluetooth: hci_qca: use wait_until_sent() for
 power pulses

On Wed, Jan 16, 2019 at 05:16:01PM +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>
> ---
> Changes in v8:
>  * Updated 1 second timeout instead of indefinite wait.
> 
> Changes in v7:
>  *  updated the wait time to 5 ms after sending power pulses.
> 
> 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 | 46 ++++++++++++++++---------------------
>  1 file changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index f036c8f98ea3..681bfa30467e 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -60,6 +60,7 @@
>  #define IBS_WAKE_RETRANS_TIMEOUT_MS	100
>  #define IBS_TX_IDLE_TIMEOUT_MS		2000
>  #define BAUDRATE_SETTLE_TIMEOUT_MS	300
> +#define POWER_PULSE_TRANS_TIMEOUT_MS	1000

nit: Not that it should make a different in normal operation, but 1s
seems extreme. Is there really any chance that the byte hasn't been
sent after say 100ms (which is still an eternity for a single byte)?

>  /* susclk rate */
>  #define SUSCLK_RATE_32KHZ	32768
> @@ -1013,11 +1014,10 @@ 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;
> +	int timeout = __msecs_to_jiffies(POWER_PULSE_TRANS_TIMEOUT_MS);

use msecs_to_jiffies()

>  	/* These power pulses are single byte command which are sent
>  	 * at required baudrate to wcn3990. On wcn3990, we have an external
> @@ -1029,22 +1029,22 @@ 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 controller", cmd);
>  
> +	serdev_device_write_flush(hu->serdev);
>  	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", 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);
> -
> -	/* Wait for 100 uS for SoC to settle down */
> -	usleep_range(100, 200);
> +	serdev_device_wait_until_sent(hu->serdev, timeout);
> +	/* Wait of 5ms is required for assuring to send the byte on the Tx
> +	 * line and also for the controller to settle down for the received
> +	 * byte.
> +	 */
> +	usleep_range(5000, 6000);

I incorrectly claimed that there might be still bytes sitting in the
UART FIFO when serdev_device_wait_until_sent() returns, Johan
corrected me on that (thanks!). So if it takes the SoC 100us to settle
down we should be good with the original code.

Cheers

Matthias