linux-kernel - Re: [PATCH v1 2/4] Bluetooth: hci_qca: Pull RTS line high for baudrate change command

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Message-ID: <25c29e35b32ca71fe6d0b02f4d6ed559@codeaurora.org>
Date:   Wed, 14 Nov 2018 12:02:16 +0530
From:   Balakrishna Godavarthi <bgodavar@...eaurora.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v1 2/4] Bluetooth: hci_qca: Pull RTS line high for
 baudrate change command

Hi Matthias,

On 2018-11-14 07:25, Matthias Kaehlcke wrote:
> On Tue, Nov 06, 2018 at 05:35:26PM +0530, Balakrishna Godavarthi wrote:
>> This patch will pull the RTS line high instead of turning off the
>> flow control, while changing baudrate of host and chip.
> 
> Please don't only describe what is changed, but also why this change
> is necessary.
> 
> IIUC the BT chip honors flow control during baudrate changes, however
> it sometimes sends 'garbage' which results in "Bluetooth: hci0: Frame
> reassembly failed (-84)" messages.
> 

[Bala]: will update the commit text.

>> Signed-off-by: Balakrishna Godavarthi <bgodavar@...eaurora.org>
>> ---
>>  drivers/bluetooth/hci_qca.c | 23 ++++++++++++-----------
>>  1 file changed, 12 insertions(+), 11 deletions(-)
>> 
>> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
>> index 051f081d1835..8301663f0004 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 +1087,14 @@ static int qca_set_speed(struct hci_uart *hu, 
>> enum qca_speed_type speed_type)
>>  		if (!speed)
>>  			return 0;
>> 
>> +		/* Pulling RTS line to high is mandatory while sending change
>> +		 * baudrate request to SoC and also while setting the host
>> +		 * baudrate.
>> +		 */
> 
> Instead of just stating that this is 'mandatory' explain why it is
> needed. Also better say 'Deassert RTS' instead of the more lower level
> 'Pulling RTS line to high'. It could be something like 'Deassert RTS
> to prevent the BT controller from sending garbage during the baudrate
> change.'
> 

[Bala]: will update the comment.

>> +		qcadev = serdev_device_get_drvdata(hu->serdev);
>> +		if (qcadev->btsoc_type == QCA_WCN3990)
>> +			serdev_device_set_rts(hu->serdev, false);
>> +
>>  		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);
>> @@ -1104,6 +1102,9 @@ static int qca_set_speed(struct hci_uart *hu, 
>> enum qca_speed_type speed_type)
>>  			return ret;
>> 
>>  		host_set_baudrate(hu, speed);
>> +
>> +		if (qcadev->btsoc_type == QCA_WCN3990)
>> +			serdev_device_set_rts(hu->serdev, true);
>>  	}
>> 
>>  	return 0;
> 
> Tested-by: Matthias Kaehlcke <mka@...omium.org>

Thanks for testing.

-- 
Regards
Balakrishna.