s3c24xx : TIOCM_CTS handling problem

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.

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

index 77ba0af..8395d5a 100644
@@ -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.

Hi,

can we add in the documentation that if the driver want to manage CTS or DCD, it should be able to report the change with uart_handle_xx_change function ?

Something like the attached patch.

Thanks

Matthieu

index 77ba0af..8395d5a 100644
@@ -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.

Ping ?

The bug is still present on git tree and I have got no replies.

Matthieu
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Send patches instead then ;)

If the chip can sense the CTS line then you could check on a timer event but it might be cleaner to add the functionality needed to allow a driver to say "always call my start_tx" method.

Hi Alan,

May be it could be usefull to do something generic that call driver get_mctrl instead of doing it in the driver (like it is done in bfin_5xx, sa1100, ...)

Or to say "recheck get_mctrl before my start_tx).
But have you got an idea how the driver could ask that to the serial core ? flags in struct uart_port seems full.

Matthieu
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html