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

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Date:   Fri, 14 Dec 2018 18:02:40 +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 2018-12-12 22:12, Johan Hovold wrote:
> On Thu, Dec 06, 2018 at 04:10:07PM +0530, 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:
> 
>> >> +	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().
> 
> No, serdev_device_write_wakeup() is currently not called in this path,
> which means you cannot use serdev_device_write().
> 
>>          Why actual we need to call an serdev_write_wakeup() is this
>> wakeup related to the UART port or for the BT chip.
> 
> serdev_device_write_wakeup() is where a writer blocked on a full write
> buffer in serdev_device_write() is woken up.
> 
> Johan

Is it preferred to use and serdev_device_write_buf() followed by 
serdev_device_wait_until_sent()
or do we required an write_wakeup() called before writing into 
serdev_device_write_buf()

-- 
Regards
Balakrishna.