On Mon, 27 Aug 2007 11:26:29 -0700
"Pallipadi, Venkatesh" [off-list ref] 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

Signed-off-by: Konstantin Baydarov <redacted>

 arch/i386/kernel/hpet.c          |   12 ++++++++++++
 arch/i386/kernel/machine_kexec.c |    6 ++++++
 include/asm-i386/hpet.h          |    3 +++
 3 files changed, 21 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

@@ -149,6 +149,18 @@ static void hpet_enable_int(void)
 	hpet_legacy_int_enabled = 1;
 }
 
+#ifdef CONFIG_KEXEC
+void hpet_disable_int(void)
+{
+	unsigned long 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)
 {

Index: linux-2.6.23-rc3/arch/i386/kernel/machine_kexec.c
===================================================================

--- linux-2.6.23-rc3.orig/arch/i386/kernel/machine_kexec.c
+++ linux-2.6.23-rc3/arch/i386/kernel/machine_kexec.c

@@ -19,6 +19,7 @@
 #include <asm/cpufeature.h>
 #include <asm/desc.h>
 #include <asm/system.h>
+#include <asm/hpet.h>
 
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
 static u32 kexec_pgd[1024] PAGE_ALIGNED;

@@ -109,6 +110,11 @@ NORET_TYPE void machine_kexec(struct kim
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
 
+#ifdef CONFIG_HPET_TIMER
+	/* Without this PIT won't work in executed kernel */
+	hpet_disable_int();
+#endif
+
 	control_page = page_address(image->control_code_page);
 	memcpy(control_page, relocate_kernel, PAGE_SIZE);
 

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