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

[Balakrishna Godavarthi]

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.