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authorDaniel Thompson <daniel.thompson@linaro.org>2014-03-28 09:28:11 +0000
committerDaniel Thompson <daniel.thompson@linaro.org>2015-07-06 13:57:46 +0100
commit29cf8a9b1453bc0037e38b511407f8fe1bd8373f (patch)
treed5b698e56678941196b934941ac4ad6dd8b30438 /lib
parentd770e558e21961ad6cfdf0ff7df0eb5d7d4f0754 (diff)
downloadlinux-29cf8a9b1453bc0037e38b511407f8fe1bd8373f.tar.gz
serial: Emulate break using control characters
Currently the magic SysRq functions are accessed by sending a break. Unfortunately some networked serial proxies makes is difficult to send a break meaning SysRq functions cannot be reached. We avoid this problem by allowing the (fairly unlikely) sequence of ^B^R^K characters to emulate a real break. This approach is very nearly as robust as normal sysrq/break handling because all trigger recognition happens during interrupt handling however to emulate a break we must enter the ISR four times (instead of twice) and manage an extra byte of state. Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.debug15
1 files changed, 15 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e2894b23efb6..9563d5315cf1 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -372,6 +372,21 @@ config MAGIC_SYSRQ_DEFAULT_ENABLE
This may be set to 1 or 0 to enable or disable them all, or
to a bitmask as described in Documentation/sysrq.txt.
+config MAGIC_SYSRQ_BREAK_EMULATION
+ bool "Enable magic SysRq serial break emulation"
+ depends on MAGIC_SYSRQ && SERIAL_CORE_CONSOLE
+ default n
+ help
+ If you say Y here, then you can use the character sequence ^B^R^K
+ to simulate a BREAK on the serial console. This is useful if for
+ some reason you cannot send a BREAK to your console's serial port.
+ For example, if you have a serial device server that cannot
+ send a BREAK. Enabling this feature can delay the delivery of
+ characters to the TTY because the ^B and a subsequent ^R will be
+ delayed until we know what the next character is.
+
+ If unsure, say N.
+
config DEBUG_KERNEL
bool "Kernel debugging"
help