Hi, there is a problem in samsung soc serial driver with the report of TIOCM_CTS in get_mctrl. The uart layer check the status of the TIOCM_CTS in the open or set_termios function and cache the result in the tty->hw_stopped flag. Then when sending data, in the function uart_start, it check tty->hw_stopped flag before calling the start_tx uart driver callback. For the samsung uart driver it means : - if the other side is not connected or in a reset state, then CTS signal is not activated - we open and configure the uart. get_mctrl don't report TIOCM_CTS flag. uart layer set tty->hw_stopped flag. - we connect or start the other side. CTS signal become activated. - we send some characters on the uart. This call uart_write which fill uart tx queue and call uart_start. uart_start doesn't call driver start_tx because tty->hw_stopped flag is set. - because driver start_tx is never call, the data is never send on the uart. >From what I see, working driver managing TIOCM_CTS flag (amba-pl011, 8250), call uart_handle_cts_change when the uart driver detect a CTS signal change (via a interrupt). Because the samsung controller doesn't generate an interrupt when CTS signal change, we can't call uart_handle_cts_change. And easy fix could be to always report TIOCM_CTS. I believe this bug is tricky and can affect other drivers. Can this be documented in Documentation/serial/driver like the attached patch ? Matthieu
diff --git a/Documentation/serial/driver b/Documentation/serial/driver index 77ba0af..8395d5a 100644 --- a/Documentation/serial/driver +++ b/Documentation/serial/driver @@ -109,6 +109,10 @@ hardware. the port does not support CTS, DCD or DSR, the driver should indicate that the signal is permanently active. If RI is not available, the signal should not be indicated as active. + If the port does not support automatic detection of change of + CTS or DCD (and report via uart_handle_cts_change or + uart_handle_dcd_change) the driver should indicate that the + signal is permanently active. Locking: port->lock taken. Interrupts: locally disabled.
