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Date:   Mon, 28 Jan 2019 19:15:48 +0530
From:   Balakrishna Godavarthi <bgodavar@codeaurora.org>
To:     Matthias Kaehlcke <mka@chromium.org>
Cc:     marcel@holtmann.org, johan.hedberg@gmail.com, johan@kernel.org,
        linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org,
        hemantg@codeaurora.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v9 2/3] Bluetooth: hci_qca: Deassert RTS while baudrate
 change command
In-Reply-To: <20190125001259.GB81583@google.com>
References: <20190124120808.8275-1-bgodavar@codeaurora.org>
 <20190124120808.8275-3-bgodavar@codeaurora.org>
 <20190125001259.GB81583@google.com>
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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@codeaurora.org>
>> Tested-by: Matthias Kaehlcke <mka@chromium.org>
>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>> 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.