1# SPDX-License-Identifier: GPL-2.0 2config TTY 3 bool "Enable TTY" if EXPERT 4 default y 5 help 6 Allows you to remove TTY support which can save space, and 7 blocks features that require TTY from inclusion in the kernel. 8 TTY is required for any text terminals or serial port 9 communication. Most users should leave this enabled. 10 11if TTY 12 13config VT 14 bool "Virtual terminal" if EXPERT 15 select INPUT 16 default y if !UML 17 help 18 If you say Y here, you will get support for terminal devices with 19 display and keyboard devices. These are called "virtual" because you 20 can run several virtual terminals (also called virtual consoles) on 21 one physical terminal. This is rather useful, for example one 22 virtual terminal can collect system messages and warnings, another 23 one can be used for a text-mode user session, and a third could run 24 an X session, all in parallel. Switching between virtual terminals 25 is done with certain key combinations, usually Alt-<function key>. 26 27 The setterm command ("man setterm") can be used to change the 28 properties (such as colors or beeping) of a virtual terminal. The 29 man page console_codes(4) ("man console_codes") contains the special 30 character sequences that can be used to change those properties 31 directly. The fonts used on virtual terminals can be changed with 32 the setfont ("man setfont") command and the key bindings are defined 33 with the loadkeys ("man loadkeys") command. 34 35 You need at least one virtual terminal device in order to make use 36 of your keyboard and monitor. Therefore, only people configuring an 37 embedded system would want to say N here in order to save some 38 memory; the only way to log into such a system is then via a serial 39 or network connection. 40 41 If unsure, say Y, or else you won't be able to do much with your new 42 shiny Linux system :-) 43 44config CONSOLE_TRANSLATIONS 45 depends on VT 46 default y 47 bool "Enable character translations in console" if EXPERT 48 help 49 This enables support for font mapping and Unicode translation 50 on virtual consoles. 51 52config VT_CONSOLE 53 bool "Support for console on virtual terminal" if EXPERT 54 depends on VT 55 default y 56 help 57 The system console is the device which receives all kernel messages 58 and warnings and which allows logins in single user mode. If you 59 answer Y here, a virtual terminal (the device used to interact with 60 a physical terminal) can be used as system console. This is the most 61 common mode of operations, so you should say Y here unless you want 62 the kernel messages be output only to a serial port (in which case 63 you should say Y to "Console on serial port", below). 64 65 If you do say Y here, by default the currently visible virtual 66 terminal (/dev/tty0) will be used as system console. You can change 67 that with a kernel command line option such as "console=tty3" which 68 would use the third virtual terminal as system console. (Try "man 69 bootparam" or see the documentation of your boot loader (lilo or 70 loadlin) about how to pass options to the kernel at boot time.) 71 72 If unsure, say Y. 73 74config VT_CONSOLE_SLEEP 75 def_bool y 76 depends on VT_CONSOLE && PM_SLEEP 77 78config VT_HW_CONSOLE_BINDING 79 bool "Support for binding and unbinding console drivers" 80 depends on VT 81 help 82 The virtual terminal is the device that interacts with the physical 83 terminal through console drivers. On these systems, at least one 84 console driver is loaded. In other configurations, additional console 85 drivers may be enabled, such as the framebuffer console. If more than 86 1 console driver is enabled, setting this to 'y' will allow you to 87 select the console driver that will serve as the backend for the 88 virtual terminals. 89 90 See <file:Documentation/driver-api/console.rst> for more 91 information. For framebuffer console users, please refer to 92 <file:Documentation/fb/fbcon.rst>. 93 94config UNIX98_PTYS 95 bool "Unix98 PTY support" if EXPERT 96 default y 97 help 98 A pseudo terminal (PTY) is a software device consisting of two 99 halves: a master and a slave. The slave device behaves identical to 100 a physical terminal; the master device is used by a process to 101 read data from and write data to the slave, thereby emulating a 102 terminal. Typical programs for the master side are telnet servers 103 and xterms. 104 105 Linux has traditionally used the BSD-like names /dev/ptyxx for 106 masters and /dev/ttyxx for slaves of pseudo terminals. This scheme 107 has a number of problems. The GNU C library glibc 2.1 and later, 108 however, supports the Unix98 naming standard: in order to acquire a 109 pseudo terminal, a process opens /dev/ptmx; the number of the pseudo 110 terminal is then made available to the process and the pseudo 111 terminal slave can be accessed as /dev/pts/<number>. What was 112 traditionally /dev/ttyp2 will then be /dev/pts/2, for example. 113 114 All modern Linux systems use the Unix98 ptys. Say Y unless 115 you're on an embedded system and want to conserve memory. 116 117config LEGACY_PTYS 118 bool "Legacy (BSD) PTY support" 119 default y 120 help 121 A pseudo terminal (PTY) is a software device consisting of two 122 halves: a master and a slave. The slave device behaves identical to 123 a physical terminal; the master device is used by a process to 124 read data from and write data to the slave, thereby emulating a 125 terminal. Typical programs for the master side are telnet servers 126 and xterms. 127 128 Linux has traditionally used the BSD-like names /dev/ptyxx 129 for masters and /dev/ttyxx for slaves of pseudo 130 terminals. This scheme has a number of problems, including 131 security. This option enables these legacy devices; on most 132 systems, it is safe to say N. 133 134config LEGACY_PTY_COUNT 135 int "Maximum number of legacy PTY in use" 136 depends on LEGACY_PTYS 137 range 0 256 138 default "256" 139 help 140 The maximum number of legacy PTYs that can be used at any one time. 141 The default is 256, and should be more than enough. Embedded 142 systems may want to reduce this to save memory. 143 144 When not in use, each legacy PTY occupies 12 bytes on 32-bit 145 architectures and 24 bytes on 64-bit architectures. 146 147config LEGACY_TIOCSTI 148 bool "Allow legacy TIOCSTI usage" 149 default y 150 help 151 Historically the kernel has allowed TIOCSTI, which will push 152 characters into a controlling TTY. This continues to be used 153 as a malicious privilege escalation mechanism, and provides no 154 meaningful real-world utility any more. Its use is considered 155 a dangerous legacy operation, and can be disabled on most 156 systems. 157 158 Say Y here only if you have confirmed that your system's 159 userspace depends on this functionality to continue operating 160 normally. 161 162 Processes which run with CAP_SYS_ADMIN, such as BRLTTY, can 163 use TIOCSTI even when this is set to N. 164 165 This functionality can be changed at runtime with the 166 dev.tty.legacy_tiocsti sysctl. This configuration option sets 167 the default value of the sysctl. 168 169config LDISC_AUTOLOAD 170 bool "Automatically load TTY Line Disciplines" 171 default y 172 help 173 Historically the kernel has always automatically loaded any 174 line discipline that is in a kernel module when a user asks 175 for it to be loaded with the TIOCSETD ioctl, or through other 176 means. This is not always the best thing to do on systems 177 where you know you will not be using some of the more 178 "ancient" line disciplines, so prevent the kernel from doing 179 this unless the request is coming from a process with the 180 CAP_SYS_MODULE permissions. 181 182 Say 'Y' here if you trust your userspace users to do the right 183 thing, or if you have only provided the line disciplines that 184 you know you will be using, or if you wish to continue to use 185 the traditional method of on-demand loading of these modules 186 by any user. 187 188 This functionality can be changed at runtime with the 189 dev.tty.ldisc_autoload sysctl, this configuration option will 190 only set the default value of this functionality. 191 192source "drivers/tty/serial/Kconfig" 193 194config SERIAL_NONSTANDARD 195 bool "Non-standard serial port support" 196 depends on HAS_IOMEM 197 help 198 Say Y here if you have any non-standard serial boards -- boards 199 which aren't supported using the standard "dumb" serial driver. 200 This includes intelligent serial boards such as 201 Digiboards, etc. These are usually used for systems that need many 202 serial ports because they serve many terminals or dial-in 203 connections. 204 205 Note that the answer to this question won't directly affect the 206 kernel: saying N will just cause the configurator to skip all 207 the questions about non-standard serial boards. 208 209 Most people can say N here. 210 211config MOXA_SMARTIO 212 tristate "Moxa SmartIO support v. 2.0" 213 depends on SERIAL_NONSTANDARD && PCI && HAS_IOPORT 214 help 215 Say Y here if you have a Moxa SmartIO multiport serial card and/or 216 want to help develop a new version of this driver. 217 218 This is upgraded (1.9.1) driver from original Moxa drivers with 219 changes finally resulting in PCI probing. 220 221 This driver can also be built as a module. The module will be called 222 mxser. If you want to do that, say M here. 223 224config N_HDLC 225 tristate "HDLC line discipline support" 226 depends on SERIAL_NONSTANDARD 227 help 228 Allows synchronous HDLC communications with tty device drivers that 229 support synchronous HDLC. 230 231 This driver can be built as a module ( = code which can be 232 inserted in and removed from the running kernel whenever you want). 233 The module will be called n_hdlc. If you want to do that, say M 234 here. 235 236config PPC_EPAPR_HV_BYTECHAN 237 bool "ePAPR hypervisor byte channel driver" 238 depends on PPC 239 select EPAPR_PARAVIRT 240 help 241 This driver creates /dev entries for each ePAPR hypervisor byte 242 channel, thereby allowing applications to communicate with byte 243 channels as if they were serial ports. 244 245config PPC_EARLY_DEBUG_EHV_BC 246 bool "Early console (udbg) support for ePAPR hypervisors" 247 depends on PPC_EPAPR_HV_BYTECHAN=y 248 help 249 Select this option to enable early console (a.k.a. "udbg") support 250 via an ePAPR byte channel. You also need to choose the byte channel 251 handle below. 252 253config PPC_EARLY_DEBUG_EHV_BC_HANDLE 254 int "Byte channel handle for early console (udbg)" 255 depends on PPC_EARLY_DEBUG_EHV_BC 256 default 0 257 help 258 If you want early console (udbg) output through a byte channel, 259 specify the handle of the byte channel to use. 260 261 For this to work, the byte channel driver must be compiled 262 in-kernel, not as a module. 263 264 Note that only one early console driver can be enabled, so don't 265 enable any others if you enable this one. 266 267 If the number you specify is not a valid byte channel handle, then 268 there simply will be no early console output. This is true also 269 if you don't boot under a hypervisor at all. 270 271config GOLDFISH_TTY 272 tristate "Goldfish TTY Driver" 273 depends on GOLDFISH 274 select SERIAL_CORE 275 select SERIAL_CORE_CONSOLE 276 help 277 Console and system TTY driver for the Goldfish virtual platform. 278 279config GOLDFISH_TTY_EARLY_CONSOLE 280 bool 281 default y if GOLDFISH_TTY=y 282 select SERIAL_EARLYCON 283 284config N_GSM 285 tristate "GSM MUX line discipline support (EXPERIMENTAL)" 286 depends on NET 287 help 288 This line discipline provides support for the GSM MUX protocol and 289 presents the mux as a set of 61 individual tty devices. 290 291config NOZOMI 292 tristate "HSDPA Broadband Wireless Data Card - Globe Trotter" 293 depends on PCI 294 help 295 If you have a HSDPA driver Broadband Wireless Data Card - 296 Globe Trotter PCMCIA card, say Y here. 297 298 To compile this driver as a module, choose M here, the module 299 will be called nozomi. 300 301config MIPS_EJTAG_FDC_TTY 302 bool "MIPS EJTAG Fast Debug Channel TTY" 303 depends on MIPS_CDMM 304 help 305 This enables a TTY and console on the MIPS EJTAG Fast Debug Channels, 306 if they are present. This can be useful when working with an EJTAG 307 probe which supports it, to get console output and a login prompt via 308 EJTAG without needing to connect a serial cable. 309 310 TTY devices are named e.g. ttyFDC3c2 (for FDC channel 2 of the FDC on 311 CPU3). 312 313 The console can be enabled with console=fdc1 (for FDC channel 1 on all 314 CPUs). Do not use the console unless there is a debug probe attached 315 to drain the FDC TX FIFO. 316 317 If unsure, say N. 318 319config MIPS_EJTAG_FDC_EARLYCON 320 bool "Early FDC console" 321 depends on MIPS_EJTAG_FDC_TTY 322 help 323 This registers a console on FDC channel 1 very early during boot (from 324 MIPS arch code). This is useful for bring-up and debugging early boot 325 issues. 326 327 Do not enable unless there is a debug probe attached to drain the FDC 328 TX FIFO. 329 330 If unsure, say N. 331 332config MIPS_EJTAG_FDC_KGDB 333 bool "Use KGDB over an FDC channel" 334 depends on MIPS_EJTAG_FDC_TTY && KGDB 335 default y 336 help 337 This enables the use of KGDB over an FDC channel, allowing KGDB to be 338 used remotely or when a serial port isn't available. 339 340config MIPS_EJTAG_FDC_KGDB_CHAN 341 int "KGDB FDC channel" 342 depends on MIPS_EJTAG_FDC_KGDB 343 range 2 15 344 default 3 345 help 346 FDC channel number to use for KGDB. 347 348config NULL_TTY 349 tristate "NULL TTY driver" 350 help 351 Say Y here if you want a NULL TTY which simply discards messages. 352 353 This is useful to allow userspace applications which expect a console 354 device to work without modifications even when no console is 355 available or desired. 356 357 In order to use this driver, you should redirect the console to this 358 TTY, boot the kernel with console=ttynull, or enable 359 NULL_TTY_DEFAULT_CONSOLE. 360 361 If unsure, say N. 362 363config NULL_TTY_DEFAULT_CONSOLE 364 bool "Support for console on ttynull" 365 depends on NULL_TTY=y && !VT_CONSOLE 366 help 367 Say Y here if you want the NULL TTY to be used as a /dev/console 368 device by default. 369 370 For example, it might be useful to prevent a VT-less kernel from 371 writing the system log to a random device connected to the serial 372 port. 373 374 Another console driver still might get preferred via the command 375 line, SPCR, or the device tree. 376 377 If unsure, say N. 378 379config VCC 380 tristate "Sun Virtual Console Concentrator" 381 depends on SUN_LDOMS 382 help 383 Support for Sun logical domain consoles. 384 385source "drivers/tty/hvc/Kconfig" 386 387config RPMSG_TTY 388 tristate "RPMSG tty driver" 389 depends on RPMSG 390 help 391 Say y here to export rpmsg endpoints as tty devices, usually found 392 in /dev/ttyRPMSGx. 393 This makes it possible for user-space programs to send and receive 394 rpmsg messages as a standard tty protocol. 395 396 To compile this driver as a module, choose M here: the module will be 397 called rpmsg_tty. 398 399endif # TTY 400 401source "drivers/tty/serdev/Kconfig" 402