| From: |
| Dave Young <hidave.darkstar@gmail.com> |
| To: |
| Linux Kernel Mailing List <linux-kernel@vger.kernel.org> |
| Subject: |
| [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase |
| Date: |
| Mon, 8 Jun 2009 15:40:07 +0800 |
| Cc: |
| Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org> |
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 that time.
The halt_delay max value is 65535, default value is 0, change it by:
echo xxx > /sys/module/printk/parameters/halt_delay
Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
---
Documentation/kernel-parameters.txt | 5 +++++
kernel/printk.c | 17 +++++++++++++++++
2 files changed, 22 insertions(+)
--- linux-2.6.orig/kernel/printk.c 2009-06-08 13:55:35.000000000 +0800
+++ linux-2.6/kernel/printk.c 2009-06-08 13:56:23.000000000 +0800
@@ -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,
char *p;
boot_delay_msec();
+ halt_delay_msec();
preempt_disable();
/* This stops the holder of console_sem just where we want him */
--- linux-2.6.orig/Documentation/kernel-parameters.txt 2009-05-28
08:40:42.000000000 +0800
+++ linux-2.6/Documentation/kernel-parameters.txt 2009-06-08
14:06:47.000000000 +0800
@@ -1897,6 +1897,11 @@ and is between 256 and 4096 characters.
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.
