--- zzzz-none-000/linux-3.10.107/Documentation/serial/driver	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/Documentation/serial/driver	2021-02-04 17:41:59.000000000 +0000
@@ -59,7 +59,9 @@
 access to the info->tmpbuf bouncebuffer used for port writes.
 
 The port_sem semaphore is used to protect against ports being added/
-removed or reconfigured at inappropriate times.
+removed or reconfigured at inappropriate times. Since v2.6.27, this
+semaphore has been the 'mutex' member of the tty_port struct, and
+commonly referred to as the port mutex (or port->mutex).
 
 
 uart_ops
@@ -140,6 +142,8 @@
 	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.
 
@@ -246,7 +250,7 @@
 	Other flags may be used (eg, xon/xoff characters) if your
 	hardware supports hardware "soft" flow control.
 
-	Locking: none.
+	Locking: caller holds port->mutex
 	Interrupts: caller dependent.
 	This call must not sleep
 
@@ -264,10 +268,6 @@
 	Locking: none.
 	Interrupts: caller dependent.
 
-  set_wake(port,state)
-	Enable/disable power management wakeup on serial activity.  Not
-	currently implemented.
-
   type(port)
 	Return a pointer to a string constant describing the specified
 	port, or return NULL, in which case the string 'unknown' is
@@ -433,3 +433,36 @@
 		struct uart_port	port;
 		int			my_stuff;
 	};
+
+Modem control lines via GPIO
+----------------------------
+
+Some helpers are provided in order to set/get modem control lines via GPIO.
+
+mctrl_gpio_init(port, idx):
+	This will get the {cts,rts,...}-gpios from device tree if they are
+	present and request them, set direction etc, and return an
+	allocated structure. devm_* functions are used, so there's no need
+	to call mctrl_gpio_free().
+	As this sets up the irq handling make sure to not handle changes to the
+	gpio input lines in your driver, too.
+
+mctrl_gpio_free(dev, gpios):
+	This will free the requested gpios in mctrl_gpio_init().
+	As devm_* function are used, there's generally no need to call
+	this function.
+
+mctrl_gpio_to_gpiod(gpios, gidx)
+	This returns the gpio structure associated to the modem line index.
+
+mctrl_gpio_set(gpios, mctrl):
+	This will sets the gpios according to the mctrl state.
+
+mctrl_gpio_get(gpios, mctrl):
+	This will update mctrl with the gpios values.
+
+mctrl_gpio_enable_ms(gpios):
+	Enables irqs and handling of changes to the ms lines.
+
+mctrl_gpio_disable_ms(gpios):
+	Disables irqs and handling of changes to the ms lines.