serial: Fix send_xchar() handlers
START_CHAR() & STOP_CHAR() can be disabled if set to '\0'
(__DISABLED_CHAR). UART drivers which define a send_xchar()
handler must not transmit __DISABLED_CHAR.
Document requirement.
Affected drivers:
sunsab
sunhv
cc: David S. Miller <davem@davemloft.net>
cc: <sparclinux@vger.kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/Documentation/serial/driver b/Documentation/serial/driver
index 3bba1ae..ba64e4b 100644
--- a/Documentation/serial/driver
+++ b/Documentation/serial/driver
@@ -140,6 +140,8 @@
will append the character to the circular buffer and then call
start_tx() / stop_tx() to flush the data out.
+ Do not transmit if ch == '\0' (__DISABLED_CHAR).
+
Locking: none.
Interrupts: caller dependent.