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Date:   Wed, 9 Jan 2019 15:52:24 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com, johan@...nel.org,
        mka@...omium.org, linux-kernel@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, hemantg@...eaurora.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate
 change command

On Thu, Dec 20, 2018 at 08:16:36PM +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@...eaurora.org>
> Tested-by: Matthias Kaehlcke <mka@...omium.org>
> Reviewed-by: Matthias Kaehlcke <mka@...omium.org>
> ---
>  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 5a07c2370289..1680ead6cc3d 100644
> --- a/drivers/bluetooth/hci_qca.c
> +++ b/drivers/bluetooth/hci_qca.c
> @@ -963,7 +963,6 @@ 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)
> @@ -977,13 +976,6 @@ 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;
> @@ -999,9 +991,6 @@ 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;
>  }
>  
> @@ -1086,6 +1075,7 @@ 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) {
> @@ -1097,6 +1087,15 @@ 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.
> +		 */
> +		qcadev = serdev_device_get_drvdata(hu->serdev);
> +		if (qcadev->btsoc_type == QCA_WCN3990)
> +			serdev_device_set_rts(hu->serdev, false);
> +

This may not do what you want unless you also disable hardware flow
control.

Johan

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