Basic braille screen reader support

This adds a minimalistic braille screen reader support.  This is meant to
be used by blind people e.g.  on boot failures or when / cannot be mounted
etc and thus the userland screen readers can not work.

[akpm@linux-foundation.org: fix exports]
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Jiri Kosina <jikos@jikos.cz>
Cc: Dmitry Torokhov <dtor@mail.ru>
Acked-by: Alan Cox <alan@redhat.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 39 insertions, 0 deletions

diff --git a/Documentation/braille-console.txt b/Documentation/braille-console.txt
new file mode 100644
index 00000000000..000b0fbdc10
--- /dev/null
+++ b/Documentation/braille-console.txt
@@ -0,0 +1,34 @@
+                       Linux Braille Console
+
+To get early boot messages on a braille device (before userspace screen
+readers can start), you first need to compile the support for the usual serial
+console (see serial-console.txt), and for braille device (in Device Drivers -
+Accessibility).
+
+Then you need to specify a console=brl, option on the kernel command line, the
+format is:
+
+        console=brl,serial_options...
+
+where serial_options... are the same as described in serial-console.txt
+
+So for instance you can use console=brl,ttyS0 if the braille device is connected
+to the first serial port, and console=brl,ttyS0,115200 to override the baud rate
+to 115200, etc.
+
+By default, the braille device will just show the last kernel message (console
+mode).  To review previous messages, press the Insert key to switch to the VT
+review mode.  In review mode, the arrow keys permit to browse in the VT content,
+page up/down keys go at the top/bottom of the screen, and the home key goes back
+to the cursor, hence providing very basic screen reviewing facility.
+
+Sound feedback can be obtained by adding the braille_console.sound=1 kernel
+parameter.
+
+For simplicity, only one braille console can be enabled, other uses of
+console=brl,... will be discarded.  Also note that it does not interfere with
+the console selection mecanism described in serial-console.txt
+
+For now, only the VisioBraille device is supported.
+
+Samuel Thibault <samuel.thibault@ens-lyon.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3ce193f8656..0ba0861b5d1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -496,6 +496,11 @@ and is between 256 and 4096 characters. It is defined in the file
                         switching to the matching ttyS device later.  The
                         options are the same as for ttyS, above.
 
+                If the device connected to the port is not a TTY but a braille
+                device, prepend "brl," before the device type, for instance
+                        console=brl,ttyS0
+                For now, only VisioBraille is supported.
+
         earlycon=       [KNL] Output early console device and options.
                 uart[8250],io,<addr>[,options]
                 uart[8250],mmio,<addr>[,options]