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

[Matthias Kaehlcke <mka@chromium.org>]

On Mon, Jun 25, 2018 at 04:43:54PM -0700, Matthias Kaehlcke wrote:
> 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@codeaurora.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?

I got that half wrong. "[v8,7/7] Bluetooth: hci_qca: Add support for
Qualcomm Bluetooth chip wcn3990" adds the flow control calls to
_set_speed() however there are still_set_flow_control() calls in
qca_setup(), which confused/s me.

Could you provide a brief summary on the situations (relevant for this
driver) in which flow controls needs to be enabled/disabled?