linux-kernel - Re: [PATCH v8 4/7] Bluetooth: hci_qca: Add wrapper functions for setting UART speed

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Message-ID: <20180625234354.GI129942@google.com>
Date:   Mon, 25 Jun 2018 16:43:54 -0700
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, devicetree@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, rtatiya@...eaurora.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v8 4/7] Bluetooth: hci_qca: Add wrapper functions for
 setting UART speed

This is a nice improvement, a few remaining questions inline.

On Mon, Jun 25, 2018 at 07:10:10PM +0530, Balakrishna Godavarthi wrote:
> In function qca_setup, we set initial and operating speeds for Qualcomm
> Bluetooth SoC's. This block of code is common across different
> Qualcomm Bluetooth SoC's. Instead of duplicating the code, created
> a wrapper function to set the speeds. So that future coming SoC's
> can use these wrapper functions to set speeds.
> 
> Signed-off-by: Balakrishna Godavarthi <bgodavar@...eaurora.org>
> ---
> Changes in v8:
>     * common function to set INIT and operating speeds.
>     * moved hardware flow control to qca_set_speed().
> 	
> Changes in v7:
>     * initial patch
>     * created wrapper functions for init and operating speeds.
> ---
>  drivers/bluetooth/hci_qca.c | 89 +++++++++++++++++++++++++++----------
>  1 file changed, 65 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> index fe62420ef838..38b7dbe6c897 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -119,6 +119,11 @@ struct qca_data {
>  	u64 votes_off;
>  };
>  
> +enum qca_speed_type {
> +	QCA_INIT_SPEED = 1,
> +	QCA_OPER_SPEED
> +};
> +
>  struct qca_serdev {
>  	struct hci_uart	 serdev_hu;
>  	struct gpio_desc *bt_en;
> @@ -923,6 +928,60 @@ static inline void host_set_baudrate(struct hci_uart *hu, unsigned int speed)
>  		hci_uart_set_baudrate(hu, speed);
>  }
>  
> +static unsigned int qca_get_speed(struct hci_uart *hu,
> +				  enum qca_speed_type speed_type)
> +{
> +	unsigned int speed = 0;
> +
> +	if (speed_type == QCA_INIT_SPEED) {
> +		if (hu->init_speed)
> +			speed = hu->init_speed;
> +		else if (hu->proto->init_speed)
> +			speed = hu->proto->init_speed;
> +	} else {
> +		if (hu->oper_speed)
> +			speed = hu->oper_speed;
> +		else if (hu->proto->oper_speed)
> +			speed = hu->proto->oper_speed;
> +	}
> +
> +	return speed;
> +}
> +
> +static int qca_set_speed(struct hci_uart *hu, enum qca_speed_type speed_type)
> +{
> +	unsigned int speed, qca_baudrate;
> +	int ret;
> +
> +	if (speed_type == QCA_INIT_SPEED) {
> +		speed = qca_get_speed(hu, QCA_INIT_SPEED);
> +		if (speed)
> +			host_set_baudrate(hu, speed);
> +		else
> +			bt_dev_err(hu->hdev, "Init speed should be non zero");

The check for 'speed == 0' is done in multiple places. From this
code I deduce that it is expected that both INIT and OPER speed are
set to non-zero values. What happens if either of them is zero? Is the
driver still operational?

> +		return 0;
> +	}
> +
> +	speed = qca_get_speed(hu, QCA_OPER_SPEED);
> +	if (!speed) {
> +		bt_dev_err(hu->hdev, "operating speed should be non zero");
> +		return 0;
> +	}
> +
> +	qca_baudrate = qca_get_baudrate_value(speed);
> +	bt_dev_info(hu->hdev, "Set UART speed to %d", speed);
> +	ret = qca_set_baudrate(hu->hdev, qca_baudrate);
> +	if (ret) {
> +		bt_dev_err(hu->hdev, "Failed to change the baudrate (%d)", ret);
> +		return ret;
> +	}
> +
> +	host_set_baudrate(hu, speed);
> +
> +	return ret;
> +}

In the discussion on "[v7,8/8] Bluetooth: hci_qca: Add support for
Qualcomm Bluetooth chip wcn3990" you mentioned the possbility to move
the hci_uart_set_flow_control() calls into _set_speed(). This seemed
interesting but finally it isn't done in this series. Did you
encounter that it is not feasible/desirable for some reason?

> +
>  static int qca_setup(struct hci_uart *hu)
>  {
>  	struct hci_dev *hdev = hu->hdev;
> @@ -937,35 +996,17 @@ static int qca_setup(struct hci_uart *hu)
>  	clear_bit(STATE_IN_BAND_SLEEP_ENABLED, &qca->flags);
>  
>  	/* Setup initial baudrate */
> -	speed = 0;
> -	if (hu->init_speed)
> -		speed = hu->init_speed;
> -	else if (hu->proto->init_speed)
> -		speed = hu->proto->init_speed;
> -
> -	if (speed)
> -		host_set_baudrate(hu, speed);
> +	qca_set_speed(hu, QCA_INIT_SPEED);
>  
>  	/* Setup user speed if needed */
> -	speed = 0;
> -	if (hu->oper_speed)
> -		speed = hu->oper_speed;
> -	else if (hu->proto->oper_speed)
> -		speed = hu->proto->oper_speed;
> +	ret = qca_set_speed(hu, QCA_OPER_SPEED);
> +	if (ret)
> +		return ret;
>  
> -	if (speed) {
> +	speed = qca_get_speed(hu, QCA_OPER_SPEED);
> +	if (speed)
>  		qca_baudrate = qca_get_baudrate_value(speed);

Is the check here necessary? qca_get_baudrate_value() returns
QCA_BAUDRATE_115200 for a zero speed.