Commit-ID: f43a6b1611aff688e21f323b64b98b57f8b7f721
Gitweb: http://git.kernel.org/tip/f43a6b1611aff688e21f323b64b98b57f8b7f721
Author: Dave Young <hidave.darkstar@xxxxxxxxx>
AuthorDate: Mon, 8 Jun 2009 15:40:07 +0800
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Mon, 8 Jun 2009 10:10:34 +0200
printk: Add halt_delay=<msecs> parameter for printk delay in halt phase
Add a halt_delay module parameter in printk.c used to read the
printk messages in halt/poweroff/restart phase, delay each
printk messages by halt_delay milliseconds.
It is useful for debugging if there's no other way to dump kernel
messages at that time. (if a system has no serial port - and if
netconsole has already gone down at that stage where the messages
are printed.)
The halt_delay max value is 65535, default value is 0. To add
a halt-day of 10 seconds, change it by:
echo 10000 > /sys/module/printk/parameters/halt_delay
Signed-off-by: Dave Young <hidave.darkstar@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
LKML-Reference: <a8e1da0906080040k7852f770v1e2aa2ebb0f52369@xxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
Documentation/kernel-parameters.txt | 5 +++++
kernel/printk.c | 17 +++++++++++++++++
2 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6172e43..0630428 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1847,6 +1847,11 @@ and is between 256 and 4096 characters. It is defined in the file
printk.time= Show timing data prefixed to each printk message line
Format: <bool> (1/Y/y=enable, 0/N/n=disable)
+ printk.halt_delay=
+ Milliseconds to delay each printk during
+ halt/poweroff/restart phase.
+ Format: <ushort>
+
processor.max_cstate= [HW,ACPI]
Limit processor to maximum C-state
max_cstate=9 overrides any DMI blacklist limit.
diff --git a/kernel/printk.c b/kernel/printk.c
index 5052b54..2114231 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -250,6 +250,22 @@ static inline void boot_delay_msec(void)
}
#endif
+/* msecs delay after each halt/poweroff/restart phase printk,
+ unsigned short is enough for delay in milliseconds */
+static unsigned short halt_delay;
+
+static inline void halt_delay_msec(void)
+{
+ if (unlikely(halt_delay == 0 || !(system_state == SYSTEM_HALT
+ || system_state == SYSTEM_POWER_OFF
+ || system_state == SYSTEM_RESTART)))
+ return;
+
+ mdelay(halt_delay);
+}
+
+module_param(halt_delay, ushort, S_IRUGO | S_IWUSR);
+
/*
* Commands to do_syslog:
*
@@ -649,6 +665,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
char *p;
boot_delay_msec();
+ halt_delay_msec();
preempt_disable();
/* This stops the holder of console_sem just where we want him */
--
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