Re: [PATCH v3 1/4] Bluetooth: hci_qca: use wait_until_sent() for power pulses

From: Balakrishna Godavarthi
Date: Fri Dec 14 2018 - 08:41:16 EST

Hi Johan,

On 2018-12-14 18:46, Johan Hovold wrote:
On Fri, Dec 14, 2018 at 06:02:40PM +0530, Balakrishna Godavarthi wrote:
Hi Johan,

On 2018-12-12 22:12, Johan Hovold wrote:
> On Thu, Dec 06, 2018 at 04:10:07PM +0530, Balakrishna Godavarthi wrote:

>> 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

That's up to the driver author and depends on what you want to achieve.

[Bala]: During the BT on & of, we need to send the commands to the controller
at a specific baudrate. as the data is getting queued in the buffer we see some times
the data is transmitting on the newer baudrate instead of the actual baudrate.
we want to achieve an synchronous data transfer for some commands to over come byte corruptions.

If you want to do something synchronously, you always have to call
serdev_device_wait_until_sent() after, as both serdev_device_write_buf()
and serdev_device_write() only buffer the data.

If you use serdev_device_write_buf() you also have to make sure that you
can handle incomplete buffering yourself (e.g. when the underlying tty
driver buffer is getting full).

serdev_device_write() was added as a convenience helper for this, but
depends on serdev_device_write_wakeup() being called in the write_wakeup
path to make forward progress.

[Bala]: Thanks for the info, now i understood the usage of the both write() and write_buf().

or do we required an write_wakeup() called before writing into

No, that doesn't make any sense. serdev_device_write_wakeup() needs to
be called in the write-wakeup path, but only if you use

Please see the documentation of these function that I added to
linux-next (and that I linked to earlier).


Thanks Johan for the detailed info.