Re: [PATCH] kexec: reenable HPET before kexec

Re: [PATCH] kexec: reenable HPET before kexec

[Eric W. Biederman]

Konstantin Baydarov <kbaidarov@ru.mvista.com> writes:

> On Mon, 27 Aug 2007 11:26:29 -0700
> "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> wrote:
>
>> 
>> 
>> - Another thing to try is to disable HPET and boot with PIT in the
>> first kernel. Just to check whether PIT never works on this platform
>> or the first kernel is doing something to stop PIT. You can try
>> "hpet=disable" boot option for that.
>> 
>> Thanks,
>> Venki
>
> I've tried kernel 1 with HPET disabled - it boots fine, PIT works!
> Then I made additional investigations and found out that PIT won't work
> in kernel 2 if bit HPET_CFG_LEGACY is set.
> Bit HPET_CFG_LEGACY is set by hpet_enable_int() during HPET
> initialization, so if this bit is cleared in machine_kexec() kernel 2
> boots fine.
> I can't explain this magic, maybe someone can explain this. Thanks.
>
> Here is new version of workaround for 2.6.23-rc3

Ok.  It looks like you understand this issue.

Can you please try calling hpet_disable_int from
hpet_set_mode under CLOCK_EVT_MODE_SHUTDOWN.  I haven't
traced the clock event methods all of the way through
but as a first approximation I think that will get
things called at the appropriate time with out needing
to patch machine_kexec.  Which is very much the wrong
place to add call any hpet code from.

We may also need to make the hpet initialization more
robust so we can do something sane in the kexec on panic
case, where we deliberately don't run any shutdown methods.

Eric

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[PATCH] kexec: reenable HPET before kexec

[Konstantin Baydarov]

On Thu, 30 Aug 2007 01:32:30 -0600
ebiederm at xmission.com (Eric W. Biederman) wrote:
> 
> Ok.  It looks like you understand this issue.
> 
> Can you please try calling hpet_disable_int from
> hpet_set_mode under CLOCK_EVT_MODE_SHUTDOWN.  I haven't
> traced the clock event methods all of the way through
> but as a first approximation I think that will get
> things called at the appropriate time with out needing
> to patch machine_kexec.  Which is very much the wrong
> place to add call any hpet code from.
> 
> We may also need to make the hpet initialization more
> robust so we can do something sane in the kexec on panic
> case, where we deliberately don't run any shutdown methods.
> 
> Eric

  Eric, actually calling hpet_disable_int() under
CLOCK_EVT_MODE_SHUTDOWN is not enough, because
HPET might not be shutdown at all (we might want to use HPET and don't
want to use LAPIC timer or in some cases HPET is used as broadcast
device with LAPIC timers enabled). So, somehow, we should call
hpet_set_mode with CLOCK_EVT_MODE_SHUTDOWN as an argument before
machine_kexec. To solve this I've added timekeeping_shutdown() to
timekeeping.c that calls clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND,
NULL). Function timekeeping_shutdown() is called from sysdev_shutdown().
  Also If we are adding hpet_disable_int() under
CLOCK_EVT_MODE_SHUTDOWN we have to add hpet_enable_int under
CLOCK_EVT_MODE_PERIODIC and CLOCK_EVT_MODE_ONESHOT.
  Also I've added call of hpet_disable_int() to machine_crash_shutdown()
because, as you said, sysdev_shutdown() won't be called on crash before
machine_kexec().
  Also, as we have to make hpet_disable_int() global and call it from
machine_crash_shutdown(), I suggest not to add hpet_disable_int() under
CLOCK_EVT_MODE_SHUTDOWN. If we don't add hpet_disable_int() under
CLOCK_EVT_MODE_SHUTDOWN - patch will be more smaller because we don't
have to call clockevents_notify() and we don't have to add
hpet_enable_int. We just have to add hpet_disable_int() call to
timekeeping_shutdown(). But it's just suggestion - attached patch adds
hpet_disable_int() under CLOCK_EVT_MODE_SHUTDOWN.

Here is new version of fix. It still against kernel 2.6.23-rc3. Thanks.

Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>

 arch/i386/kernel/crash.c  |    4 ++++
 arch/i386/kernel/hpet.c   |   33 +++++++++++++++++++++++++++++++++
 include/asm-i386/hpet.h   |    3 +++
 kernel/time/timekeeping.c |   13 +++++++++++++
 4 files changed, 53 insertions(+)

Index: linux-2.6.23-rc3/arch/i386/kernel/hpet.c
===================================================================
--- linux-2.6.23-rc3.orig/arch/i386/kernel/hpet.c
+++ linux-2.6.23-rc3/arch/i386/kernel/hpet.c
@@ -144,11 +144,35 @@ static void hpet_enable_int(void)
 {
 	unsigned long cfg = hpet_readl(HPET_CFG);
 
+#ifdef CONFIG_KEXEC
+	if (hpet_legacy_int_enabled)
+		return;
+#endif
+
 	cfg |= HPET_CFG_LEGACY;
 	hpet_writel(cfg, HPET_CFG);
 	hpet_legacy_int_enabled = 1;
 }
 
+#ifdef CONFIG_KEXEC
+void hpet_disable_int(void)
+{
+	unsigned long cfg;
+
+	if (!hpet_legacy_int_enabled)
+		return;
+
+	if (!is_hpet_capable())
+		return;
+
+	cfg = hpet_readl(HPET_CFG);
+	cfg &= ~HPET_CFG_LEGACY;
+	hpet_writel(cfg, HPET_CFG);
+	hpet_legacy_int_enabled = 0;
+
+}
+#endif
+
 static void hpet_set_mode(enum clock_event_mode mode,
 			  struct clock_event_device *evt)
 {
@@ -157,6 +181,9 @@ static void hpet_set_mode(enum clock_eve
 
 	switch(mode) {
 	case CLOCK_EVT_MODE_PERIODIC:
+#ifdef CONFIG_KEXEC
+		hpet_enable_int();
+#endif
 		delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * hpet_clockevent.mult;
 		delta >>= hpet_clockevent.shift;
 		now = hpet_readl(HPET_COUNTER);
@@ -176,6 +203,9 @@ static void hpet_set_mode(enum clock_eve
 		break;
 
 	case CLOCK_EVT_MODE_ONESHOT:
+#ifdef CONFIG_KEXEC
+		hpet_enable_int();
+#endif
 		cfg = hpet_readl(HPET_T0_CFG);
 		cfg &= ~HPET_TN_PERIODIC;
 		cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
@@ -187,6 +217,9 @@ static void hpet_set_mode(enum clock_eve
 		cfg = hpet_readl(HPET_T0_CFG);
 		cfg &= ~HPET_TN_ENABLE;
 		hpet_writel(cfg, HPET_T0_CFG);
+#ifdef CONFIG_KEXEC
+		hpet_disable_int();
+#endif
 		break;
 
 	case CLOCK_EVT_MODE_RESUME:
Index: linux-2.6.23-rc3/include/asm-i386/hpet.h
===================================================================
--- linux-2.6.23-rc3.orig/include/asm-i386/hpet.h
+++ linux-2.6.23-rc3/include/asm-i386/hpet.h
@@ -66,6 +66,9 @@
 extern unsigned long hpet_address;
 extern int is_hpet_enabled(void);
 extern int hpet_enable(void);
+#ifdef CONFIG_KEXEC
+extern void hpet_disable_int(void);
+#endif
 
 #ifdef CONFIG_HPET_EMULATE_RTC
 
Index: linux-2.6.23-rc3/arch/i386/kernel/crash.c
===================================================================
--- linux-2.6.23-rc3.orig/arch/i386/kernel/crash.c
+++ linux-2.6.23-rc3/arch/i386/kernel/crash.c
@@ -24,6 +24,7 @@
 #include <asm/apic.h>
 #include <linux/kdebug.h>
 #include <asm/smp.h>
+#include <asm/hpet.h>
 
 #include <mach_ipi.h>
 
@@ -128,6 +129,9 @@ void machine_crash_shutdown(struct pt_re
 
 	/* Make a note of crashing cpu. Will be used in NMI callback.*/
 	crashing_cpu = safe_smp_processor_id();
+#ifdef CONFIG_KEXEC
+	hpet_disable_int();
+#endif
 	nmi_shootdown_cpus();
 	lapic_shutdown();
 #if defined(CONFIG_X86_IO_APIC)
Index: linux-2.6.23-rc3/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.23-rc3.orig/kernel/time/timekeeping.c
+++ linux-2.6.23-rc3/kernel/time/timekeeping.c
@@ -335,8 +335,21 @@ static int timekeeping_suspend(struct sy
 	return 0;
 }
 
+#ifdef CONFIG_KEXEC
+static int timekeeping_shutdown(struct sys_device *dev)
+{
+	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
+//	hpet_disable_int();
+
+	return 0;
+}
+#endif
+
 /* sysfs resume/suspend bits for timekeeping */
 static struct sysdev_class timekeeping_sysclass = {
+#ifdef CONFIG_KEXEC
+	.shutdown	= timekeeping_shutdown,
+#endif
 	.resume		= timekeeping_resume,
 	.suspend	= timekeeping_suspend,
 	set_kset_name("timekeeping"),

Re: [PATCH] kexec: reenable HPET before kexec

[Eric W. Biederman]

Konstantin Baydarov <kbaidarov@ru.mvista.com> writes:

>   Eric, actually calling hpet_disable_int() under
> CLOCK_EVT_MODE_SHUTDOWN is not enough, because
> HPET might not be shutdown at all (we might want to use HPET and don't
> want to use LAPIC timer or in some cases HPET is used as broadcast
> device with LAPIC timers enabled). So, somehow, we should call
> hpet_set_mode with CLOCK_EVT_MODE_SHUTDOWN as an argument before
> machine_kexec. To solve this I've added timekeeping_shutdown() to
> timekeeping.c that calls clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND,
> NULL). Function timekeeping_shutdown() is called from sysdev_shutdown().

Is suspend the right thing?  The fact that time keeping seems
to be reinventing the standard infrastructure for shutting
down instead of just reusing it has me a bit confused.

Regardless hooking into the shutdown is the right thing
to do here.

>   Also If we are adding hpet_disable_int() under
> CLOCK_EVT_MODE_SHUTDOWN we have to add hpet_enable_int under
> CLOCK_EVT_MODE_PERIODIC and CLOCK_EVT_MODE_ONESHOT.

However that works.  I just know that in the device tree we
have shutdown methods that are called on reboot and kexec
and the hpet needs one, and that is where the code belongs.

I was assuming that CLOCK_EVT_MODE_SHUTDOWN just mapped
to the shutdown method of the clock events or something else.
But it shutdown means something different in this context we
can certainly find a better place to hook into the device
tree and call shutdown methods.   Especially if that will
make the code simpler.

>   Also I've added call of hpet_disable_int() to machine_crash_shutdown()
> because, as you said, sysdev_shutdown() won't be called on crash before
> machine_kexec().

This is a design feature.  machine_crash_shutdown is not really 
supposed to disable any hardware.  There is a very minimal set that we
haven't been able to figure out how to get the kernels initialization
routines to deal with properly.  Which is a temporary justification
for not doing more now.  If we can't find anyway to make the
initialization code more robust for the hpet we can revisit this.

>   Also, as we have to make hpet_disable_int() global and call it from
> machine_crash_shutdown(), I suggest not to add hpet_disable_int() under
> CLOCK_EVT_MODE_SHUTDOWN. If we don't add hpet_disable_int() under
> CLOCK_EVT_MODE_SHUTDOWN - patch will be more smaller because we don't
> have to call clockevents_notify() and we don't have to add
> hpet_enable_int. We just have to add hpet_disable_int() call to
> timekeeping_shutdown(). But it's just suggestion - attached patch adds
> hpet_disable_int() under CLOCK_EVT_MODE_SHUTDOWN.

Please remove the CONFIG_KEXEC.  We need to do this on a reboot also
so we don't confuse the BIOS.  BIOS's frequently but not always
can just reset the board to avoid complications like this, but if
we need a shutdown method we need a shutdown method.  The kexec
case just exercises things more.

Please can we ignore the machine_crash_shutdown path for the moment.
And revisit it again after we have the normal case fixed.

Adding hpet_disable_int into timekeeping_shutdown at first glance
looks like a layering and maintenance violation.

Eric

> Here is new version of fix. It still against kernel 2.6.23-rc3. Thanks.
>
> Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>
>
>  arch/i386/kernel/crash.c  |    4 ++++
>  arch/i386/kernel/hpet.c   |   33 +++++++++++++++++++++++++++++++++
>  include/asm-i386/hpet.h   |    3 +++
>  kernel/time/timekeeping.c |   13 +++++++++++++
>  4 files changed, 53 insertions(+)
>
> Index: linux-2.6.23-rc3/arch/i386/kernel/hpet.c
> ===================================================================
> --- linux-2.6.23-rc3.orig/arch/i386/kernel/hpet.c
> +++ linux-2.6.23-rc3/arch/i386/kernel/hpet.c
> @@ -144,11 +144,35 @@ static void hpet_enable_int(void)
>  {
>  	unsigned long cfg = hpet_readl(HPET_CFG);
>  
> +#ifdef CONFIG_KEXEC
> +	if (hpet_legacy_int_enabled)
> +		return;
> +#endif

Why do we need this test only for kexec?
> +
>  	cfg |= HPET_CFG_LEGACY;
>  	hpet_writel(cfg, HPET_CFG);
>  	hpet_legacy_int_enabled = 1;
>  }
>  
> +#ifdef CONFIG_KEXEC
> +void hpet_disable_int(void)
> +{
> +	unsigned long cfg;
> +
> +	if (!hpet_legacy_int_enabled)
> +		return;
> +
> +	if (!is_hpet_capable())
> +		return;
> +
> +	cfg = hpet_readl(HPET_CFG);
> +	cfg &= ~HPET_CFG_LEGACY;
> +	hpet_writel(cfg, HPET_CFG);
> +	hpet_legacy_int_enabled = 0;
> +
> +}
> +#endif
> +
>  static void hpet_set_mode(enum clock_event_mode mode,
>  			  struct clock_event_device *evt)
>  {
> @@ -157,6 +181,9 @@ static void hpet_set_mode(enum clock_eve
>  
>  	switch(mode) {
>  	case CLOCK_EVT_MODE_PERIODIC:
> +#ifdef CONFIG_KEXEC
> +		hpet_enable_int();
> +#endif
>  		delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * hpet_clockevent.mult;
>  		delta >>= hpet_clockevent.shift;
>  		now = hpet_readl(HPET_COUNTER);
> @@ -176,6 +203,9 @@ static void hpet_set_mode(enum clock_eve
>  		break;
>  
>  	case CLOCK_EVT_MODE_ONESHOT:
> +#ifdef CONFIG_KEXEC
> +		hpet_enable_int();
> +#endif
>  		cfg = hpet_readl(HPET_T0_CFG);
>  		cfg &= ~HPET_TN_PERIODIC;
>  		cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
> @@ -187,6 +217,9 @@ static void hpet_set_mode(enum clock_eve
>  		cfg = hpet_readl(HPET_T0_CFG);
>  		cfg &= ~HPET_TN_ENABLE;
>  		hpet_writel(cfg, HPET_T0_CFG);
> +#ifdef CONFIG_KEXEC
> +		hpet_disable_int();
> +#endif
>  		break;
>  
>  	case CLOCK_EVT_MODE_RESUME:
> Index: linux-2.6.23-rc3/include/asm-i386/hpet.h
> ===================================================================
> --- linux-2.6.23-rc3.orig/include/asm-i386/hpet.h
> +++ linux-2.6.23-rc3/include/asm-i386/hpet.h
> @@ -66,6 +66,9 @@
>  extern unsigned long hpet_address;
>  extern int is_hpet_enabled(void);
>  extern int hpet_enable(void);
> +#ifdef CONFIG_KEXEC
> +extern void hpet_disable_int(void);
> +#endif
>  
>  #ifdef CONFIG_HPET_EMULATE_RTC
>  
> Index: linux-2.6.23-rc3/arch/i386/kernel/crash.c
> ===================================================================
> --- linux-2.6.23-rc3.orig/arch/i386/kernel/crash.c
> +++ linux-2.6.23-rc3/arch/i386/kernel/crash.c
> @@ -24,6 +24,7 @@
>  #include <asm/apic.h>
>  #include <linux/kdebug.h>
>  #include <asm/smp.h>
> +#include <asm/hpet.h>
>  
>  #include <mach_ipi.h>
>  
> @@ -128,6 +129,9 @@ void machine_crash_shutdown(struct pt_re
>  
>  	/* Make a note of crashing cpu. Will be used in NMI callback.*/
>  	crashing_cpu = safe_smp_processor_id();
> +#ifdef CONFIG_KEXEC
> +	hpet_disable_int();
> +#endif
>  	nmi_shootdown_cpus();
>  	lapic_shutdown();
>  #if defined(CONFIG_X86_IO_APIC)
> Index: linux-2.6.23-rc3/kernel/time/timekeeping.c
> ===================================================================
> --- linux-2.6.23-rc3.orig/kernel/time/timekeeping.c
> +++ linux-2.6.23-rc3/kernel/time/timekeeping.c
> @@ -335,8 +335,21 @@ static int timekeeping_suspend(struct sy
>  	return 0;
>  }
>  
> +#ifdef CONFIG_KEXEC
> +static int timekeeping_shutdown(struct sys_device *dev)
> +{
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
Hmm.  Do we want to add a CLOCK_EVT_NOTIFY_SHUTDOWN?
Would that make anything simpler?
> +//	hpet_disable_int();
> +
> +	return 0;
> +}
> +#endif
> +
>  /* sysfs resume/suspend bits for timekeeping */
>  static struct sysdev_class timekeeping_sysclass = {
> +#ifdef CONFIG_KEXEC
> +	.shutdown	= timekeeping_shutdown,
> +#endif
>  	.resume		= timekeeping_resume,
>  	.suspend	= timekeeping_suspend,
>  	set_kset_name("timekeeping"),

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[PATCH] kexec: reenable HPET before kexec

[Konstantin Baydarov]

On Thu, 30 Aug 2007 12:04:33 -0600
ebiederm at xmission.com (Eric W. Biederman) wrote:

> I was assuming that CLOCK_EVT_MODE_SHUTDOWN just mapped
> to the shutdown method of the clock events or something else.
> But it shutdown means something different in this context we
> can certainly find a better place to hook into the device
> tree and call shutdown methods.   Especially if that will
> make the code simpler.

Agree. I've got rig from timekeeping. Now I'm using system device tree shutdown interface, as you suggested. I've added HPET system device class with shutdown method and HPET device to sysdev.

> This is a design feature.  machine_crash_shutdown is not really 
> supposed to disable any hardware.  There is a very minimal set that we
> haven't been able to figure out how to get the kernels initialization
> routines to deal with properly.  Which is a temporary justification
> for not doing more now.  If we can't find anyway to make the
> initialization code more robust for the hpet we can revisit this.

So you suggest to check if HPET is present in HPET init code even if HPET disabled in boot kernel command line or APIC is disabled. And if HPET is present and kernel not going to use it - disable HPET interrupts?

> Please remove the CONFIG_KEXEC.  We need to do this on a reboot also
> so we don't confuse the BIOS.  BIOS's frequently but not always
> can just reset the board to avoid complications like this, but if
> we need a shutdown method we need a shutdown method.  The kexec
> case just exercises things more.
Removed CONFIG_KEXEC.

So here is new version of fix. Patch against 2.6.23-rc3.
Eric, review please. Thanks.

Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>

 arch/i386/kernel/hpet.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

Index: linux-2.6.23-rc3/arch/i386/kernel/hpet.c
===================================================================
--- linux-2.6.23-rc3.orig/arch/i386/kernel/hpet.c
+++ linux-2.6.23-rc3/arch/i386/kernel/hpet.c
@@ -144,11 +144,31 @@ static void hpet_enable_int(void)
 {
 	unsigned long cfg = hpet_readl(HPET_CFG);
 
+	if (hpet_legacy_int_enabled)
+		return;
+
 	cfg |= HPET_CFG_LEGACY;
 	hpet_writel(cfg, HPET_CFG);
 	hpet_legacy_int_enabled = 1;
 }
 
+static void hpet_disable_int(void)
+{
+	unsigned long cfg;
+
+	if (!hpet_legacy_int_enabled)
+		return;
+
+	if (!is_hpet_capable())
+		return;
+
+	cfg = hpet_readl(HPET_CFG);
+	cfg &= ~HPET_CFG_LEGACY;
+	hpet_writel(cfg, HPET_CFG);
+	hpet_legacy_int_enabled = 0;
+
+}
+
 static void hpet_set_mode(enum clock_event_mode mode,
 			  struct clock_event_device *evt)
 {
@@ -551,3 +571,31 @@ irqreturn_t hpet_rtc_interrupt(int irq, 
 	return IRQ_HANDLED;
 }
 #endif
+
+static int hpet_shutdown(struct sys_device *dev)
+{
+	/* We need this to make PIT works in KEXECuted kernel */
+	hpet_disable_int();
+
+	return 0;
+}
+
+static struct sysdev_class hpet_sysdev_class = {
+	set_kset_name("hpet"),
+	.shutdown = hpet_shutdown,
+};
+
+static struct sys_device device_hpet = {
+	.id	= 0,
+	.cls	= &hpet_sysdev_class,
+};
+
+static int __init hpet_init_sysfs(void)
+{
+	int error = sysdev_class_register(&hpet_sysdev_class);
+	if (!error)
+		error = sysdev_register(&device_hpet);
+	return error;
+}
+
+device_initcall(hpet_init_sysfs);

[PATCH] kexec: reenable HPET before kexec

[Konstantin Baydarov]

On Fri, 31 Aug 2007 14:31:51 +0400
Konstantin Baydarov <kbaidarov@ru.mvista.com> wrote:

> On Thu, 30 Aug 2007 12:04:33 -0600
> ebiederm at xmission.com (Eric W. Biederman) wrote:
> 
> > I was assuming that CLOCK_EVT_MODE_SHUTDOWN just mapped
> > to the shutdown method of the clock events or something else.
> > But it shutdown means something different in this context we
> > can certainly find a better place to hook into the device
> > tree and call shutdown methods.   Especially if that will
> > make the code simpler.
> 
> Agree. I've got rig from timekeeping. Now I'm using system device
> tree shutdown interface, as you suggested. I've added HPET system
> device class with shutdown method and HPET device to sysdev.
> 
> > This is a design feature.  machine_crash_shutdown is not really 
> > supposed to disable any hardware.  There is a very minimal set that
> > we haven't been able to figure out how to get the kernels
> > initialization routines to deal with properly.  Which is a
> > temporary justification for not doing more now.  If we can't find
> > anyway to make the initialization code more robust for the hpet we
> > can revisit this.
> 
> So you suggest to check if HPET is present in HPET init code even if
> HPET disabled in boot kernel command line or APIC is disabled. And if
> HPET is present and kernel not going to use it - disable HPET
> interrupts?
> 
> > Please remove the CONFIG_KEXEC.  We need to do this on a reboot also
> > so we don't confuse the BIOS.  BIOS's frequently but not always
> > can just reset the board to avoid complications like this, but if
> > we need a shutdown method we need a shutdown method.  The kexec
> > case just exercises things more.
> Removed CONFIG_KEXEC.
> 
> So here is new version of fix. Patch against 2.6.23-rc3.
> Eric, review please. Thanks.
> 
> Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>
> 
>  arch/i386/kernel/hpet.c |   48
> ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48
> insertions(+)
> 
> Index: linux-2.6.23-rc3/arch/i386/kernel/hpet.c
> ===================================================================
> --- linux-2.6.23-rc3.orig/arch/i386/kernel/hpet.c
> +++ linux-2.6.23-rc3/arch/i386/kernel/hpet.c
> @@ -144,11 +144,31 @@ static void hpet_enable_int(void)
>  {
>  	unsigned long cfg = hpet_readl(HPET_CFG);
>  
> +	if (hpet_legacy_int_enabled)
> +		return;
> +
>  	cfg |= HPET_CFG_LEGACY;
>  	hpet_writel(cfg, HPET_CFG);
>  	hpet_legacy_int_enabled = 1;
>  }
>  
> +static void hpet_disable_int(void)
> +{
> +	unsigned long cfg;
> +
> +	if (!hpet_legacy_int_enabled)
> +		return;
> +
> +	if (!is_hpet_capable())
> +		return;
> +
> +	cfg = hpet_readl(HPET_CFG);
> +	cfg &= ~HPET_CFG_LEGACY;
> +	hpet_writel(cfg, HPET_CFG);
> +	hpet_legacy_int_enabled = 0;
> +
> +}
> +
>  static void hpet_set_mode(enum clock_event_mode mode,
>  			  struct clock_event_device *evt)
>  {
> @@ -551,3 +571,31 @@ irqreturn_t hpet_rtc_interrupt(int irq, 
>  	return IRQ_HANDLED;
>  }
>  #endif
> +
> +static int hpet_shutdown(struct sys_device *dev)
> +{
> +	/* We need this to make PIT works in KEXECuted kernel */
> +	hpet_disable_int();
> +
> +	return 0;
> +}
> +
> +static struct sysdev_class hpet_sysdev_class = {
> +	set_kset_name("hpet"),
> +	.shutdown = hpet_shutdown,
> +};
> +
> +static struct sys_device device_hpet = {
> +	.id	= 0,
> +	.cls	= &hpet_sysdev_class,
> +};
> +
> +static int __init hpet_init_sysfs(void)
> +{
> +	int error = sysdev_class_register(&hpet_sysdev_class);
> +	if (!error)
> +		error = sysdev_register(&device_hpet);
> +	return error;
> +}
> +
> +device_initcall(hpet_init_sysfs);
> -
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  Eric, can you tell me, when are you going to review last version of fix?
  Thanks.