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

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Date:   Thu, 06 Dec 2018 16:10:07 +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 2018-12-05 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

-- 
Regards
Balakrishna.