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
