Re: [PATCH v9 2/3] Bluetooth: hci_qca: Deassert RTS while baudrate change command

[Balakrishna Godavarthi]

Hi Matthias,

On 2019-01-25 05:42, Matthias Kaehlcke wrote:
> Hi Balakrishna,
>
> On Thu, Jan 24, 2019 at 05:38:07PM +0530, Balakrishna Godavarthi wrote:
> > This patch will help to stop frame reassembly errors while changing
> > the baudrate. This is because host send a change baudrate request
> > command to the chip with 115200 bps, Whereas chip will change their
> > UART clocks to the enable for new baudrate and sends the response
> > for the change request command with newer baudrate, On host side
> > we are still operating in 115200 bps which results of reading garbage
> > data. Here we are pulling RTS line, so that chip we will wait to send 
> > data
> > to host until host change its baudrate.
> >
> > Signed-off-by: Balakrishna Godavarthi <bgodavar@xxxxxxxxxxxxxx>
> > Tested-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > ---
> > Changes in v9:
> >  * disabled flow control while setting the baudrate of HOST and chip.
> > ---
> >  drivers/bluetooth/hci_qca.c | 24 +++++++++++++-----------
> >  1 file changed, 13 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index c08f4d105e73..6b5bcd44e24c 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -964,7 +964,6 @@ static int qca_set_baudrate(struct hci_dev *hdev, 
> > uint8_t baudrate)
> >  	struct hci_uart *hu = hci_get_drvdata(hdev);
> >  	struct qca_data *qca = hu->priv;
> >  	struct sk_buff *skb;
> > -	struct qca_serdev *qcadev;
> >  	u8 cmd[] = { 0x01, 0x48, 0xFC, 0x01, 0x00 };
> >
> >  	if (baudrate > QCA_BAUDRATE_3200000)
> > @@ -978,13 +977,6 @@ static int qca_set_baudrate(struct hci_dev *hdev, 
> > uint8_t baudrate)
> >  		return -ENOMEM;
> >  	}
> >
> > -	/* Disabling hardware flow control is mandatory while
> > -	 * sending change baudrate request to wcn3990 SoC.
> > -	 */
> > -	qcadev = serdev_device_get_drvdata(hu->serdev);
> > -	if (qcadev->btsoc_type == QCA_WCN3990)
> > -		hci_uart_set_flow_control(hu, true);
> > -
> >  	/* Assign commands to change baudrate and packet type. */
> >  	skb_put_data(skb, cmd, sizeof(cmd));
> >  	hci_skb_pkt_type(skb) = HCI_COMMAND_PKT;
> > @@ -1000,9 +992,6 @@ static int qca_set_baudrate(struct hci_dev *hdev, 
> > uint8_t baudrate)
> >  	schedule_timeout(msecs_to_jiffies(BAUDRATE_SETTLE_TIMEOUT_MS));
> >  	set_current_state(TASK_RUNNING);
> >
> > -	if (qcadev->btsoc_type == QCA_WCN3990)
> > -		hci_uart_set_flow_control(hu, false);
> > -
> >  	return 0;
> >  }
> >
> > @@ -1089,6 +1078,7 @@ static int qca_check_speeds(struct hci_uart *hu)
> >  static int qca_set_speed(struct hci_uart *hu, enum qca_speed_type 
> > speed_type)
> >  {
> >  	unsigned int speed, qca_baudrate;
> > +	struct qca_serdev *qcadev;
> >  	int ret;
> >
> >  	if (speed_type == QCA_INIT_SPEED) {
> > @@ -1100,6 +1090,15 @@ static int qca_set_speed(struct hci_uart *hu, 
> > enum qca_speed_type speed_type)
> >  		if (!speed)
> >  			return 0;
> >
> > +		/* Deassert RTS while changing the baudrate of chip and host.
> > +		 * This will prevent chip from transmitting its response with
> > +		 * the new baudrate while the host port is still operating at
> > +		 * the old speed.
> > +		 */
>
> It is not necessarily evident which action deasserts RTS, I suggest to
> rephrase it to something like:
>
> "Disable flow control for wcn3990 to deassert RTS while ... "

[Bala]: will update.

> > +		qcadev = serdev_device_get_drvdata(hu->serdev);
> > +		if (qcadev->btsoc_type == QCA_WCN3990)
> > +			hci_uart_set_flow_control(hu, true);
> > +
> >  		qca_baudrate = qca_get_baudrate_value(speed);
> >  		bt_dev_dbg(hu->hdev, "Set UART speed to %d", speed);
> >  		ret = qca_set_baudrate(hu->hdev, qca_baudrate);
>
> flow control should be re-enabled in the error path.
>
> Cheers
>
> Matthias

[Bala; will update.

--
Regards
Balakrishna.