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SubjectRe: [PATCH v6 1/6] Bluetooth: hci_qca: use wait_until_sent() for power pulses
HI Matthias,

On 2018-12-28 01:48, Matthias Kaehlcke wrote:
> On Thu, Dec 27, 2018 at 01:01:31PM +0530, Balakrishna Godavarthi wrote:
>> wcn3990 requires a power pulse to turn ON/OFF along with
>> regulators. Sometimes we are observing the power pulses are sent
>> out with some time delay, due to queuing these commands. This is
>> causing synchronization issues with chip, which intern delay the
>> chip setup or may end up with communication issues.
>>
>> Signed-off-by: Balakrishna Godavarthi <bgodavar@codeaurora.org>
>> ---
>> Changes in v6:
>> * added serdev_device_write_flush() in qca_send_power_pulse
>> instead during the power off pulse.
>>
>> Changes in v5:
>> * added serdev_device_write_flush() in qca_power_off().
>>
>> ---
>> drivers/bluetooth/hci_qca.c | 38
>> ++++++++++++++-----------------------
>> 1 file changed, 14 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
>> index f036c8f98ea3..507a2355c758 100644
>> --- a/drivers/bluetooth/hci_qca.c
>> +++ b/drivers/bluetooth/hci_qca.c
>> @@ -1013,11 +1013,9 @@ static inline void host_set_baudrate(struct
>> hci_uart *hu, unsigned int speed)
>> hci_uart_set_baudrate(hu, speed);
>> }
>>
>> -static int qca_send_power_pulse(struct hci_dev *hdev, u8 cmd)
>> +static int qca_send_power_pulse(struct hci_uart *hu, u8 cmd)
>> {
>> - struct hci_uart *hu = hci_get_drvdata(hdev);
>> - struct qca_data *qca = hu->priv;
>> - struct sk_buff *skb;
>> + int ret;
>>
>> /* These power pulses are single byte command which are sent
>> * at required baudrate to wcn3990. On wcn3990, we have an external
>> @@ -1029,19 +1027,17 @@ static int qca_send_power_pulse(struct hci_dev
>> *hdev, u8 cmd)
>> * save power. Disabling hardware flow control is mandatory while
>> * sending power pulses to SoC.
>> */
>> - bt_dev_dbg(hdev, "sending power pulse %02x to SoC", cmd);
>> -
>> - skb = bt_skb_alloc(sizeof(cmd), GFP_KERNEL);
>> - if (!skb)
>> - return -ENOMEM;
>> -
>> + serdev_device_write_flush(hu->serdev);
>> + bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
>
> nit: why clutter the code flow by putting the log statement in the
> middle of code that is actually doing something with the serial
> interface?
>
> In case you respin anyway I suggest to structure it like this:
>
> bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
>
> hci_uart_set_flow_control(hu, true);
> serdev_device_write_flush(hu->serdev);
> ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd));
>
>
>> hci_uart_set_flow_control(hu, true);
>> + ret = serdev_device_write_buf(hu->serdev, &cmd, sizeof(cmd));
>> + if (ret < 0) {
>> + bt_dev_err(hu->hdev, "failed to send power pulse %02x to SoC",
>
> nit: especially on 'embedded' devices 'SoC' is typically associated
> with the CPU running Linux, you might want to change it to
> 'controller'.
>

[Bala]: will update.

>> + cmd);
>> + return ret;
>> + }
>>
>> - skb_put_u8(skb, cmd);
>> - hci_skb_pkt_type(skb) = HCI_COMMAND_PKT;
>> -
>> - skb_queue_tail(&qca->txq, skb);
>> - hci_uart_tx_wakeup(hu);
>> + serdev_device_wait_until_sent(hu->serdev, 0);
>>
>> /* Wait for 100 uS for SoC to settle down */
>> usleep_range(100, 200);
>
> I said earlier the delay here should be enough to ensure that the byte
> gets transferred from a hardware buffer/FIFO to the controller,
> however that didn't take into account that the power pulses are sent
> with a baudrate of 2400. That translates to ~240 bytes/s, hence a
> delay of 5 ms is needed to be on the safe side.
>

[Bala]: sure will update the delay of 5 ms.

> In case you change the delay please also update the comment to make
> clear this is not only time for the BT controller to settle, but also
> to guarantee that the command was actually sent to the controller.
>

[Bala]: will update the comment.

> So far it seems no problems have been observed, though this could be
> thanks to the 100 ms delay in qca_wcn3990_init().
>
> Cheers
>
> Matthias

--
Regards
Balakrishna.

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