tty: Added a CONFIG_TTY option to allow removal of TTY

The option allows you to remove TTY and compile without errors. This
saves space on systems that won't support TTY interfaces anyway.
bloat-o-meter output is below.

The bulk of this patch consists of Kconfig changes adding "depends on
TTY" to various serial devices and similar drivers that require the TTY
layer.  Ideally, these dependencies would occur on a common intermediate
symbol such as SERIO, but most drivers "select SERIO" rather than
"depends on SERIO", and "select" does not respect dependencies.

bloat-o-meter output comparing our previous minimal to new minimal by
removing TTY.  The list is filtered to not show removed entries with awk
'$3 != "-"' as the list was very long.

add/remove: 0/226 grow/shrink: 2/14 up/down: 6/-35356 (-35350)
function                                     old     new   delta
chr_dev_init                                 166     170      +4
allow_signal                                  80      82      +2
static.__warned                              143     142      -1
disallow_signal                               63      62      -1
__set_special_pids                            95      94      -1
unregister_console                           126     121      -5
start_kernel                                 546     541      -5
register_console                             593     588      -5
copy_from_user                                45      40      -5
sys_setsid                                   128     120      -8
sys_vhangup                                   32      19     -13
do_exit                                     1543    1526     -17
bitmap_zero                                   60      40     -20
arch_local_irq_save                          137     117     -20
release_task                                 674     652     -22
static.spin_unlock_irqrestore                308     260     -48

Signed-off-by: Joe Millenbach <jmillenbach@gmail.com>
Reviewed-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 21 insertions, 1 deletions

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 0ecf22b6a38e..a79fd8ebd56e 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -1,3 +1,14 @@
+config TTY
+        bool "Enable TTY" if EXPERT
+        default y
+        ---help---
+          Allows you to remove TTY support which can save space, and
+          blocks features that require TTY from inclusion in the kernel.
+          TTY is required for any text terminals or serial port
+          communication. Most users should leave this enabled.
+
+if TTY
+
 config VT
         bool "Virtual terminal" if EXPERT
         depends on !S390 && !UML
@@ -388,3 +399,5 @@ config PPC_EARLY_DEBUG_EHV_BC_HANDLE
           If the number you specify is not a valid byte channel handle, then
           there simply will be no early console output.  This is true also
           if you don't boot under a hypervisor at all.
+
+endif # TTY
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 2953059530e4..df5663d0d55e 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -1,4 +1,4 @@
-obj-y                           += tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
+obj-$(CONFIG_TTY)               += tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
                                    tty_buffer.o tty_port.o tty_mutex.o
 obj-$(CONFIG_LEGACY_PTYS)       += pty.o
 obj-$(CONFIG_UNIX98_PTYS)       += pty.o
diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index f47b734c6a7a..8902f9b4df71 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -1,3 +1,5 @@
+if TTY
+
 config HVC_DRIVER
         bool
         help
@@ -119,3 +121,4 @@ config HVCS
           which will also be compiled when this driver is built as a
           module.
 
+endif # TTY
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 2dc429357fe3..e9aeccdfbe35 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -2,6 +2,8 @@
 # Serial device configuration
 #
 
+if TTY
+
 menu "Serial drivers"
         depends on HAS_IOMEM
 
@@ -1483,3 +1485,5 @@ config SERIAL_RP2_NR_UARTS
           need to be increased.
 
 endmenu
+
+endif # TTY