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

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Message-ID: <20181114015504.GH22824@google.com>
Date:   Tue, 13 Nov 2018 17:55:04 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Balakrishna Godavarthi <bgodavar@...eaurora.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

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.

> 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.'

> +		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>