[patch] suspend debugging: simulate suspend-to-RAM

[Ingo Molnar <mingo@elte.hu>]

Subject: [patch] suspend debugging: simulate suspend-to-RAM
From: Ingo Molnar <mingo@elte.hu>

most resume bugs are due to the kernel hanging or crashing while trying 
to resume a specific device. It is extremely hard to debug such hangs 
because often when the hang happens there's no console available yet.

Make debugging such bugs easier by offering a resume mode that does not 
actually call into the BIOS to turn off the machine. This, in 
combination with earlyprintk=serial,ttyS0,115200,keep , 
CONFIG_PM_DEBUG=y, CONFIG_DISABLE_CONSOLE_SUSPEND=y and 
/sys/power/filter enables me to have a fully functional serial console 
during the full suspend/resume cycle.

I debugged two suspend bugs in the -rt kernel this way already, so it's 
pretty useful.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 Documentation/kernel-parameters.txt |    4 ++++
 drivers/acpi/sleep/main.c           |   15 ++++++++++++++-
 include/linux/acpi.h                |    1 +
 kernel/sysctl.c                     |   16 ++++++++++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)

Index: linux/Documentation/kernel-parameters.txt
===================================================================
--- linux.orig/Documentation/kernel-parameters.txt
+++ linux/Documentation/kernel-parameters.txt
@@ -159,6 +159,10 @@ and is between 256 and 4096 characters. 
 
 	acpi_osi=	[HW,ACPI] empty param disables _OSI
 
+	acpi_simulate_suspend_to_ram
+			[KNL] Do not call into BIOS to do suspend-to-RAM
+			Format: <0/1>
+
 	acpi_serialize	[HW,ACPI] force serialization of AML methods
 
 	acpi_skip_timer_override [HW,ACPI]
Index: linux/drivers/acpi/sleep/main.c
===================================================================
--- linux.orig/drivers/acpi/sleep/main.c
+++ linux/drivers/acpi/sleep/main.c
@@ -35,6 +35,14 @@ static u32 acpi_suspend_states[] = {
 
 static int init_8259A_after_S1;
 
+/*
+ * simulate entry into the BIOS - this way the system will not
+ * be turned off for real, and the kernel's resume functionality
+ * can be debugged while still having some system capabilities
+ * left. This is especially useful in combination with /sys/power/filter.
+ */
+int acpi_simulate_suspend_to_ram;
+
 /**
  *	acpi_pm_prepare - Do preliminary suspend work.
  *	@pm_state:		suspend state we're entering.
@@ -91,7 +99,12 @@ static int acpi_pm_enter(suspend_state_t
 		break;
 
 	case PM_SUSPEND_MEM:
-		do_suspend_lowlevel();
+		if (unlikely(acpi_simulate_suspend_to_ram)) {
+			printk(KERN_INFO "ACPI: simulating suspend-to-RAM: "
+					 "not calling BIOS.\n");
+		} else {
+			do_suspend_lowlevel();
+		}
 		break;
 
 	case PM_SUSPEND_DISK:
Index: linux/include/linux/acpi.h
===================================================================
--- linux.orig/include/linux/acpi.h
+++ linux/include/linux/acpi.h
@@ -438,6 +438,7 @@ extern int pci_mmcfg_config_num;
 
 extern int sbf_port;
 extern unsigned long acpi_video_flags;
+extern int acpi_simulate_suspend_to_ram;
 
 #else	/* !CONFIG_ACPI */
 
Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c
+++ linux/kernel/sysctl.c
@@ -329,6 +329,14 @@ static ctl_table kern_table[] = {
 		.proc_handler	= &proc_dointvec,
 	},
 	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "futex_performance_hack",
+		.data		= &futex_performance_hack,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
+	{
 		.ctl_name	= KERN_PANIC,
 		.procname	= "prof_pid",
 		.data		= &prof_pid,
@@ -908,6 +916,14 @@ static ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_doulongvec_minmax,
 	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "acpi_simulate_suspend_to_ram",
+		.data		= &acpi_simulate_suspend_to_ram,
+		.maxlen		= sizeof (int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 #endif
 #ifdef CONFIG_IA64
 	{