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SubjectRe: [PATCH 1/5] RT kernel: force detect HPET from PCI space

On Sat, 31 Mar 2007, Nicolas Mailhot wrote:

> [adding some people in CC that expressed interest in the problem before]
> I'm crazy enough to test a patch if someone cooks it, but I'm way out of
> my depth there :)

After struggling with totally broken kernels for the whole morning I got the
HPET to work with my NForce4 with the following hard coded ACPI quirk. My
machine has been now stable for few hours and I tested that the HPET really
seems to be working by switching the clock source using

echo hpet|tsc|acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource

Results of a simple benchmark show that the time to execute gettimeofday
really varies based on the clock source: (performance normalised to tsc)
tsc: 1x
hpet: 4x
acpi_pm: 12x

At least on my motherboard it seems to be enough to just grab the HPET address
from the lspci output and not bother with any of the other changing bits.

--- linux-2.6.21-rc5-git5/arch/i386/kernel/acpi/boot.c 2007-03-31 17:49:24.000000000 +0300
+++ linux-2.6.21-rc5-git5.hpet/arch/i386/kernel/acpi/boot.c 2007-03-31 17:02:27.000000000 +0300
@@ -1189,6 +1189,8 @@ int __init acpi_boot_table_init(void)

int __init acpi_boot_init(void)
+ struct acpi_table_hpet hpet_tbl;
* If acpi_disabled, bail out
* One exception: acpi=ht continues far enough to enumerate LAPICs
@@ -1208,7 +1210,12 @@ int __init acpi_boot_init(void)

- acpi_table_parse(ACPI_SIG_HPET, acpi_parse_hpet);
+ hpet_tbl.address.address = 0xfefff000L;
+ hpet_tbl.address.space_id = ACPI_SPACE_MEM;
+ hpet_tbl.sequence = 0;
+ = 0xbabe;
+ acpi_parse_hpet((struct acpi_table_header *) &hpet_tbl);
+ // acpi_table_parse(ACPI_SIG_HPET, acpi_parse_hpet);

return 0;
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