On Mon, 27 Aug 2007 11:26:29 -0700
"Pallipadi, Venkatesh" <venkatesh.pallipadi@xxxxxxxxx> 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 <kbaidarov@xxxxxxxxxxxxx>
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
-
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