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SubjectRe: [PATCH v3 1/4] Bluetooth: hci_qca: use wait_until_sent() for power pulses
Hi Johan,

On 2018-12-06 16:10, Balakrishna Godavarthi wrote:
> Hi Johan,
>
> On 2018-12-05 11:55, Johan Hovold wrote:
>> On Fri, Nov 30, 2018 at 08:32:44PM +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>
>>> ---
>>> v3:
>>> * no change.
>>> v2:
>>> * Updated function qca_send_power_pulse()
>>> * addressed reviewer comments.
>>
>> Please make sure to include reviewers on CC when resending, and as
>> someone else already mentioned, be a bit more specific about what
>> changes you actually made in response to the review feedback you
>> received.
>>
>
> [Bala]: sure will add and provide more info in version change history.
>
>>> v1:
>>> * initial patch
>>> ---
>>> drivers/bluetooth/hci_qca.c | 37
>>> +++++++++++++------------------------
>>> 1 file changed, 13 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/bluetooth/hci_qca.c
>>> b/drivers/bluetooth/hci_qca.c
>>> index f036c8f98ea3..f5dd323c1967 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 +1027,16 @@ 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;
>>> -
>>> + bt_dev_dbg(hu->hdev, "sending power pulse %02x to SoC", cmd);
>>> hci_uart_set_flow_control(hu, true);
>>> + ret = serdev_device_write(hu->serdev, &cmd, sizeof(cmd), 0);
>>
>> You're still using 0 as a timeout here which is broken, as I already
>> told you.
>>
>
> [Bala]: got the change now will update to timeout to non zero value.
>
>> From 4.21 this will result in an indefinite timeout, but currently
>> implies not to wait for a full write buffer to drain at all.
>>
>> As I also mentioned, you need to to make sure to call
>> serdev_device_write_wakeup() in the write_wakup() path if you are
>> going
>> to use serdev_device_write() at all.
>>
>
> [Bala]: this where i am confused.
> calling serdev_device_write is calling an wakeup internally.
> below is the flow
>
> ttyport_write_buf:
> * calling serdev_device_write() will call write_buf() in
> this call we are enabling bit "TTY_DO_WRITE_WAKEUP" and calling
> write()
> i.e. uart_write() where we call in start_tx. this will
> go to the vendor specific write where in isr we call
> uart_write_wakeup()
>
> https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/qcom_geni_serial.c#L756
>
>
> uart_write_wakeup()->ttyport_write_wakeup()->serdev_controller_write_wakeup()->hci_uart_write_wakeup()->hci_uart_tx_wakeup()
>
> the above is flow when serdev_device_write() is called, it is
> indirectly calling serdev_write_wakeup().
>
> Why actual we need to call an serdev_write_wakeup() is this
> wakeup related to the UART port or for the BT chip.
>
>> Johan

Can you help me to understand, whether my understating is correct wrt
serdev_wakeup().

--
Regards
Balakrishna.

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