[SERIAL] Clean up and fix tty transmission start/stoping

The start_tx and stop_tx methods were passed a flag to indicate
whether the start/stop was from the tty start/stop callbacks, and
some drivers used this flag to decide whether to ask the UART to
immediately stop transmission (where the UART supports such a
feature.)

There are other cases when we wish this to occur - when CTS is
lowered, or if we change from soft to hard flow control and CTS
is inactive.  In these cases, this flag was false, and we would
allow the transmitter to drain before stopping.

There is really only one case where we want to let the transmitter
drain before disabling, and that's when we run out of characters
to send.

Hence, re-jig the start_tx and stop_tx methods to eliminate this
flag, and introduce new functions for the special "disable and
allow transmitter to drain" case.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 11 deletions

diff --git a/Documentation/serial/driver b/Documentation/serial/driver
index ac7eabbf662a..87856d3cfb67 100644
--- a/Documentation/serial/driver
+++ b/Documentation/serial/driver
@@ -111,24 +111,17 @@ hardware.
         Interrupts: locally disabled.
         This call must not sleep
 
-  stop_tx(port,tty_stop)
+  stop_tx(port)
         Stop transmitting characters.  This might be due to the CTS
         line becoming inactive or the tty layer indicating we want
-        to stop transmission.
-
-        tty_stop: 1 if this call is due to the TTY layer issuing a
-                  TTY stop to the driver (equiv to rs_stop).
+        to stop transmission due to an XOFF character.
 
         Locking: port->lock taken.
         Interrupts: locally disabled.
         This call must not sleep
 
-  start_tx(port,tty_start)
-        start transmitting characters.  (incidentally, nonempty will
-        always be nonzero, and shouldn't be used - it will be dropped).
-
-        tty_start: 1 if this call was due to the TTY layer issuing
-                   a TTY start to the driver (equiv to rs_start)
+  start_tx(port)
+        start transmitting characters.
 
         Locking: port->lock taken.
         Interrupts: locally disabled.