linux-kernel - Re: [PATCH v3 1/4] Bluetooth: hci_qca: use wait_until

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Date:   Tue, 11 Dec 2018 21:12:34 +0530
From:   Balakrishna Godavarthi <bgodavar@...eaurora.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     marcel@...tmann.org, johan.hedberg@...il.com, mka@...omium.org,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        hemantg@...eaurora.org, linux-arm-msm@...r.kernel.org,
        Johan Hovold <jhovold@...il.com>
Subject: Re: [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@...eaurora.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.