1 files changed, 16 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
index ad22fb0ee765..9eb3c2b6b040 100644
--- a/Documentation/ABI/testing/sysfs-tty
+++ b/Documentation/ABI/testing/sysfs-tty
@@ -138,3 +138,19 @@ Description:
 
                  These sysfs values expose the TIOCGSERIAL interface via
                  sysfs rather than via ioctls.
+
+What:           /sys/class/tty/ttyS0/rx_trig_bytes
+Date:           May 2014
+Contact:        Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
+Description:
+                 Shows current RX interrupt trigger bytes or sets the
+                 user specified value to change it for the FIFO buffer.
+                 Users can show or set this value regardless of opening the
+                 serial device file or not.
+
+                 The RX trigger can be set one of four kinds of values for UART
+                 serials. When users input a meaning less value to this I/F,
+                 the RX trigger is changed to the nearest lower value for the
+                 device specification. For example, when user sets 7bytes on
+                 16550A, which has 1/4/8/14 bytes trigger, the RX trigger is
+                 automatically changed to 4 bytes.