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

From: Balakrishna Godavarthi
Date: Fri Dec 14 2018 - 07:32:48 EST

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

* 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()


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.


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()