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

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