4 files changed, 165 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
new file mode 100644
index 00000000000..b138b663bf5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-tty
@@ -0,0 +1,19 @@
+What:           /sys/class/tty/console/active
+Date:           Nov 2010
+Contact:        Kay Sievers <kay.sievers@vrfy.org>
+Description:
+                 Shows the list of currently configured
+                 console devices, like 'tty1 ttyS0'.
+                 The last entry in the file is the active
+                 device connected to /dev/console.
+                 The file supports poll() to detect virtual
+                 console switches.
+
+What:           /sys/class/tty/tty0/active
+Date:           Nov 2010
+Contact:        Kay Sievers <kay.sievers@vrfy.org>
+Description:
+                 Shows the currently active virtual console
+                 device, like 'tty1'.
+                 The file supports poll() to detect virtual
+                 console switches.
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index e73df2722ff..9471225212c 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1181,6 +1181,30 @@ Table 1-12: Files in /proc/fs/ext4/<devname>
  mb_groups       details of multiblock allocator buddy cache of free blocks
 ..............................................................................
 
+2.0 /proc/consoles
+------------------
+Shows registered system console lines.
+
+To see which character device lines are currently used for the system console
+/dev/console, you may simply look into the file /proc/consoles:
+
+  > cat /proc/consoles
+  tty0                 -WU (ECp)       4:7
+  ttyS0                -W- (Ep)        4:64
+
+The columns are:
+
+  device               name of the device
+  operations           R = can do read operations
+                       W = can do write operations
+                       U = can do unblank
+  flags                E = it is enabled
+                       C = it is prefered console
+                       B = it is primary boot console
+                       p = it is used for printk buffer
+                       b = it is not a TTY but a Braille device
+                       a = it is safe to use when cpu is offline
+  major:minor          major and minor number of the device separated by a colon
 
 ------------------------------------------------------------------------------
 Summary
diff --git a/Documentation/serial/00-INDEX b/Documentation/serial/00-INDEX
index 07dcdb0d2a3..e09468ad3cb 100644
--- a/Documentation/serial/00-INDEX
+++ b/Documentation/serial/00-INDEX
@@ -14,6 +14,8 @@ riscom8.txt
         - notes on using the RISCom/8 multi-port serial driver.
 rocket.txt
         - info on the Comtrol RocketPort multiport serial driver.
+serial-rs485.txt
+        - info about RS485 structures and support in the kernel.
 specialix.txt
         - info on hardware/driver for specialix IO8+ multiport serial card.
 stallion.txt
diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt
new file mode 100644
index 00000000000..a4932387bbf
--- /dev/null
+++ b/Documentation/serial/serial-rs485.txt
@@ -0,0 +1,120 @@
+                        RS485 SERIAL COMMUNICATIONS
+
+1. INTRODUCTION
+
+   EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the
+   electrical characteristics of drivers and receivers for use in balanced
+   digital multipoint systems.
+   This standard is widely used for communications in industrial automation
+   because it can be used effectively over long distances and in electrically
+   noisy environments.
+
+2. HARDWARE-RELATED CONSIDERATIONS
+
+   Some CPUs/UARTs (e.g., Atmel AT91 or 16C950 UART) contain a built-in
+   half-duplex mode capable of automatically controlling line direction by
+   toggling RTS or DTR signals. That can be used to control external
+   half-duplex hardware like an RS485 transceiver or any RS232-connected
+   half-duplex devices like some modems.
+
+   For these microcontrollers, the Linux driver should be made capable of
+   working in both modes, and proper ioctls (see later) should be made
+   available at user-level to allow switching from one mode to the other, and
+   vice versa.
+
+3. DATA STRUCTURES ALREADY AVAILABLE IN THE KERNEL
+
+   The Linux kernel provides the serial_rs485 structure (see [1]) to handle
+   RS485 communications. This data structure is used to set and configure RS485
+   parameters in the platform data and in ioctls.
+
+   Any driver for devices capable of working both as RS232 and RS485 should
+   provide at least the following ioctls:
+
+    - TIOCSRS485 (typically associated with number 0x542F). This ioctl is used
+      to enable/disable RS485 mode from user-space
+
+    - TIOCGRS485 (typically associated with number 0x542E). This ioctl is used
+      to get RS485 mode from kernel-space (i.e., driver) to user-space.
+
+   In other words, the serial driver should contain a code similar to the next
+   one:
+
+        static struct uart_ops atmel_pops = {
+                /* ... */
+                .ioctl          = handle_ioctl,
+        };
+
+        static int handle_ioctl(struct uart_port *port,
+                unsigned int cmd,
+                unsigned long arg)
+        {
+                struct serial_rs485 rs485conf;
+
+                switch (cmd) {
+                case TIOCSRS485:
+                        if (copy_from_user(&rs485conf,
+                                (struct serial_rs485 *) arg,
+                                sizeof(rs485conf)))
+                                        return -EFAULT;
+
+                        /* ... */
+                        break;
+
+                case TIOCGRS485:
+                        if (copy_to_user((struct serial_rs485 *) arg,
+                                ...,
+                                sizeof(rs485conf)))
+                                        return -EFAULT;
+                        /* ... */
+                        break;
+
+                /* ... */
+                }
+        }
+
+
+4. USAGE FROM USER-LEVEL
+
+   From user-level, RS485 configuration can be get/set using the previous
+   ioctls. For instance, to set RS485 you can use the following code:
+
+        #include <linux/serial.h>
+
+        /* Driver-specific ioctls: */
+        #define TIOCGRS485      0x542E
+        #define TIOCSRS485      0x542F
+
+        /* Open your specific device (e.g., /dev/mydevice): */
+        int fd = open ("/dev/mydevice", O_RDWR);
+        if (fd < 0) {
+                /* Error handling. See errno. */
+        }
+
+        struct serial_rs485 rs485conf;
+
+        /* Set RS485 mode: */
+        rs485conf.flags |= SER_RS485_ENABLED;
+
+        /* Set rts delay before send, if needed: */
+        rs485conf.flags |= SER_RS485_RTS_BEFORE_SEND;
+        rs485conf.delay_rts_before_send = ...;
+
+        /* Set rts delay after send, if needed: */
+        rs485conf.flags |= SER_RS485_RTS_AFTER_SEND;
+        rs485conf.delay_rts_after_send = ...;
+
+        if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
+                /* Error handling. See errno. */
+        }
+
+        /* Use read() and write() syscalls here... */
+
+        /* Close the device when finished: */
+        if (close (fd) < 0) {
+                /* Error handling. See errno. */
+        }
+
+5. REFERENCES
+
+ [1]    include/linux/serial.h