linux-yocto/drivers/tty/Kconfig

SPDX-License-Identifier: GPL-2.0

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 select INPUT default y if !UML help If you say Y here, you will get support for terminal devices with display and keyboard devices. These are called "virtual" because you can run several virtual terminals (also called virtual consoles) on one physical terminal. This is rather useful, for example one virtual terminal can collect system messages and warnings, another one can be used for a text-mode user session, and a third could run an X session, all in parallel. Switching between virtual terminals is done with certain key combinations, usually Alt-.

  The setterm command ("man setterm") can be used to change the
  properties (such as colors or beeping) of a virtual terminal. The
  man page console_codes(4) ("man console_codes") contains the special
  character sequences that can be used to change those properties
  directly. The fonts used on virtual terminals can be changed with
  the setfont ("man setfont") command and the key bindings are defined
  with the loadkeys ("man loadkeys") command.

  You need at least one virtual terminal device in order to make use
  of your keyboard and monitor. Therefore, only people configuring an
  embedded system would want to say N here in order to save some
  memory; the only way to log into such a system is then via a serial
  or network connection.

  If unsure, say Y, or else you won't be able to do much with your new
  shiny Linux system :-)

config CONSOLE_TRANSLATIONS depends on VT default y bool "Enable character translations in console" if EXPERT help This enables support for font mapping and Unicode translation on virtual consoles.

config VT_CONSOLE bool "Support for console on virtual terminal" if EXPERT depends on VT default y help The system console is the device which receives all kernel messages and warnings and which allows logins in single user mode. If you answer Y here, a virtual terminal (the device used to interact with a physical terminal) can be used as system console. This is the most common mode of operations, so you should say Y here unless you want the kernel messages be output only to a serial port (in which case you should say Y to "Console on serial port", below).

  If you do say Y here, by default the currently visible virtual
  terminal (/dev/tty0) will be used as system console. You can change
  that with a kernel command line option such as "console=tty3" which
  would use the third virtual terminal as system console. (Try "man
  bootparam" or see the documentation of your boot loader (lilo or
  loadlin) about how to pass options to the kernel at boot time.)

  If unsure, say Y.

config VT_CONSOLE_SLEEP def_bool y depends on VT_CONSOLE && PM_SLEEP

config VT_HW_CONSOLE_BINDING bool "Support for binding and unbinding console drivers" depends on VT help The virtual terminal is the device that interacts with the physical terminal through console drivers. On these systems, at least one console driver is loaded. In other configurations, additional console drivers may be enabled, such as the framebuffer console. If more than 1 console driver is enabled, setting this to 'y' will allow you to select the console driver that will serve as the backend for the virtual terminals.

  See <file:Documentation/driver-api/console.rst> for more
  information. For framebuffer console users, please refer to
  <file:Documentation/fb/fbcon.rst>.

config UNIX98_PTYS bool "Unix98 PTY support" if EXPERT default y help A pseudo terminal (PTY) is a software device consisting of two halves: a master and a slave. The slave device behaves identical to a physical terminal; the master device is used by a process to read data from and write data to the slave, thereby emulating a terminal. Typical programs for the master side are telnet servers and xterms.

  Linux has traditionally used the BSD-like names /dev/ptyxx for
  masters and /dev/ttyxx for slaves of pseudo terminals. This scheme
  has a number of problems. The GNU C library glibc 2.1 and later,
  however, supports the Unix98 naming standard: in order to acquire a
  pseudo terminal, a process opens /dev/ptmx; the number of the pseudo
  terminal is then made available to the process and the pseudo
  terminal slave can be accessed as /dev/pts/<number>. What was
  traditionally /dev/ttyp2 will then be /dev/pts/2, for example.

  All modern Linux systems use the Unix98 ptys.  Say Y unless
  you're on an embedded system and want to conserve memory.

config LEGACY_PTYS bool "Legacy (BSD) PTY support" default y help A pseudo terminal (PTY) is a software device consisting of two halves: a master and a slave. The slave device behaves identical to a physical terminal; the master device is used by a process to read data from and write data to the slave, thereby emulating a terminal. Typical programs for the master side are telnet servers and xterms.

  Linux has traditionally used the BSD-like names /dev/ptyxx
  for masters and /dev/ttyxx for slaves of pseudo
  terminals. This scheme has a number of problems, including
  security.  This option enables these legacy devices; on most
  systems, it is safe to say N.

config LEGACY_PTY_COUNT int "Maximum number of legacy PTY in use" depends on LEGACY_PTYS range 0 256 default "256" help The maximum number of legacy PTYs that can be used at any one time. The default is 256, and should be more than enough. Embedded systems may want to reduce this to save memory.

  When not in use, each legacy PTY occupies 12 bytes on 32-bit
  architectures and 24 bytes on 64-bit architectures.

config LEGACY_TIOCSTI bool "Allow legacy TIOCSTI usage" default y help Historically the kernel has allowed TIOCSTI, which will push characters into a controlling TTY. This continues to be used as a malicious privilege escalation mechanism, and provides no meaningful real-world utility any more. Its use is considered a dangerous legacy operation, and can be disabled on most systems.

  Say Y here only if you have confirmed that your system's
  userspace depends on this functionality to continue operating
  normally.

  Processes which run with CAP_SYS_ADMIN, such as BRLTTY, can
  use TIOCSTI even when this is set to N.

  This functionality can be changed at runtime with the
  dev.tty.legacy_tiocsti sysctl. This configuration option sets
  the default value of the sysctl.

config LDISC_AUTOLOAD bool "Automatically load TTY Line Disciplines" default y help Historically the kernel has always automatically loaded any line discipline that is in a kernel module when a user asks for it to be loaded with the TIOCSETD ioctl, or through other means. This is not always the best thing to do on systems where you know you will not be using some of the more "ancient" line disciplines, so prevent the kernel from doing this unless the request is coming from a process with the CAP_SYS_MODULE permissions.

  Say 'Y' here if you trust your userspace users to do the right
  thing, or if you have only provided the line disciplines that
  you know you will be using, or if you wish to continue to use
  the traditional method of on-demand loading of these modules
  by any user.

  This functionality can be changed at runtime with the
  dev.tty.ldisc_autoload sysctl, this configuration option will
  only set the default value of this functionality.

source "drivers/tty/serial/Kconfig"

config SERIAL_NONSTANDARD bool "Non-standard serial port support" depends on HAS_IOMEM help Say Y here if you have any non-standard serial boards -- boards which aren't supported using the standard "dumb" serial driver. This includes intelligent serial boards such as Digiboards, etc. These are usually used for systems that need many serial ports because they serve many terminals or dial-in connections.

  Note that the answer to this question won't directly affect the
  kernel: saying N will just cause the configurator to skip all
  the questions about non-standard serial boards.

  Most people can say N here.

config MOXA_INTELLIO tristate "Moxa Intellio support" depends on SERIAL_NONSTANDARD && (ISA || EISA || PCI) select FW_LOADER help Say Y here if you have a Moxa Intellio multiport serial card.

  To compile this driver as a module, choose M here: the
  module will be called moxa.

config MOXA_SMARTIO tristate "Moxa SmartIO support v. 2.0" depends on SERIAL_NONSTANDARD && PCI help Say Y here if you have a Moxa SmartIO multiport serial card and/or want to help develop a new version of this driver.

  This is upgraded (1.9.1) driver from original Moxa drivers with
  changes finally resulting in PCI probing.

  This driver can also be built as a module. The module will be called
  mxser. If you want to do that, say M here.

config SYNCLINK_GT tristate "SyncLink GT/AC support" depends on SERIAL_NONSTANDARD && PCI depends on BROKEN help Support for SyncLink GT and SyncLink AC families of synchronous and asynchronous serial adapters manufactured by Microgate Systems, Ltd. (www.microgate.com)

config N_HDLC tristate "HDLC line discipline support" depends on SERIAL_NONSTANDARD help Allows synchronous HDLC communications with tty device drivers that support synchronous HDLC such as the Microgate SyncLink adapter.

  This driver can be built as a module ( = code which can be
  inserted in and removed from the running kernel whenever you want).
  The module will be called n_hdlc. If you want to do that, say M
  here.

config PPC_EPAPR_HV_BYTECHAN bool "ePAPR hypervisor byte channel driver" depends on PPC select EPAPR_PARAVIRT help This driver creates /dev entries for each ePAPR hypervisor byte channel, thereby allowing applications to communicate with byte channels as if they were serial ports.

config PPC_EARLY_DEBUG_EHV_BC bool "Early console (udbg) support for ePAPR hypervisors" depends on PPC_EPAPR_HV_BYTECHAN=y help Select this option to enable early console (a.k.a. "udbg") support via an ePAPR byte channel. You also need to choose the byte channel handle below.

config PPC_EARLY_DEBUG_EHV_BC_HANDLE int "Byte channel handle for early console (udbg)" depends on PPC_EARLY_DEBUG_EHV_BC default 0 help If you want early console (udbg) output through a byte channel, specify the handle of the byte channel to use.

  For this to work, the byte channel driver must be compiled
  in-kernel, not as a module.

  Note that only one early console driver can be enabled, so don't
  enable any others if you enable this one.

  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.

config GOLDFISH_TTY tristate "Goldfish TTY Driver" depends on GOLDFISH select SERIAL_CORE select SERIAL_CORE_CONSOLE help Console and system TTY driver for the Goldfish virtual platform.

config GOLDFISH_TTY_EARLY_CONSOLE bool default y if GOLDFISH_TTY=y select SERIAL_EARLYCON

config IPWIRELESS tristate "IPWireless 3G UMTS PCMCIA card support" depends on PCMCIA && NETDEVICES select PPP help This is a driver for 3G UMTS PCMCIA card from IPWireless company. In some countries (for example Czech Republic, T-Mobile ISP) this card is shipped for service called UMTS 4G.

config N_GSM tristate "GSM MUX line discipline support (EXPERIMENTAL)" depends on NET help This line discipline provides support for the GSM MUX protocol and presents the mux as a set of 61 individual tty devices.

config NOZOMI tristate "HSDPA Broadband Wireless Data Card - Globe Trotter" depends on PCI help If you have a HSDPA driver Broadband Wireless Data Card - Globe Trotter PCMCIA card, say Y here.

  To compile this driver as a module, choose M here, the module
  will be called nozomi.

config MIPS_EJTAG_FDC_TTY bool "MIPS EJTAG Fast Debug Channel TTY" depends on MIPS_CDMM help This enables a TTY and console on the MIPS EJTAG Fast Debug Channels, if they are present. This can be useful when working with an EJTAG probe which supports it, to get console output and a login prompt via EJTAG without needing to connect a serial cable.

  TTY devices are named e.g. ttyFDC3c2 (for FDC channel 2 of the FDC on
  CPU3).

  The console can be enabled with console=fdc1 (for FDC channel 1 on all
  CPUs). Do not use the console unless there is a debug probe attached
  to drain the FDC TX FIFO.

  If unsure, say N.

config MIPS_EJTAG_FDC_EARLYCON bool "Early FDC console" depends on MIPS_EJTAG_FDC_TTY help This registers a console on FDC channel 1 very early during boot (from MIPS arch code). This is useful for bring-up and debugging early boot issues.

  Do not enable unless there is a debug probe attached to drain the FDC
  TX FIFO.

  If unsure, say N.

config MIPS_EJTAG_FDC_KGDB bool "Use KGDB over an FDC channel" depends on MIPS_EJTAG_FDC_TTY && KGDB default y help This enables the use of KGDB over an FDC channel, allowing KGDB to be used remotely or when a serial port isn't available.

config MIPS_EJTAG_FDC_KGDB_CHAN int "KGDB FDC channel" depends on MIPS_EJTAG_FDC_KGDB range 2 15 default 3 help FDC channel number to use for KGDB.

config NULL_TTY tristate "NULL TTY driver" help Say Y here if you want a NULL TTY which simply discards messages.

  This is useful to allow userspace applications which expect a console
  device to work without modifications even when no console is
  available or desired.

  In order to use this driver, you should redirect the console to this
  TTY, or boot the kernel with console=ttynull.

  If unsure, say N.

config VCC tristate "Sun Virtual Console Concentrator" depends on SUN_LDOMS help Support for Sun logical domain consoles.

source "drivers/tty/hvc/Kconfig"

config RPMSG_TTY tristate "RPMSG tty driver" depends on RPMSG help Say y here to export rpmsg endpoints as tty devices, usually found in /dev/ttyRPMSGx. This makes it possible for user-space programs to send and receive rpmsg messages as a standard tty protocol.

  To compile this driver as a module, choose M here: the module will be
  called rpmsg_tty.

endif # TTY

source "drivers/tty/serdev/Kconfig"