From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764421AbYEARfp (ORCPT ); Thu, 1 May 2008 13:35:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760910AbYEARfT (ORCPT ); Thu, 1 May 2008 13:35:19 -0400 Received: from gateway-1237.mvista.com ([63.81.120.158]:9729 "EHLO dwalker1.mvista.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1760398AbYEARfR (ORCPT ); Thu, 1 May 2008 13:35:17 -0400 Message-Id: <20080501173123.444094226@mvista.com> User-Agent: quilt/0.46-1 Date: Thu, 01 May 2008 10:31:23 -0700 From: Daniel Walker To: akpm@linux-foundation.org Cc: johnstul@us.ibm.com, ralf@linux-mips.org, linux-kernel@vger.kernel.org Subject: [PATCH] clocksource: shift helper Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a little helper I pulled from the mips tree. I've seen a couple of bogus shift values, and this helper calculates the shift. This should move the shift selection away from the user, and systematically pick the value base on the hz. I also modified the acpi_pm timer to use this new interface. The original shift was 22 , and after this patch it's increased to 23. Which should make the clocksource slightly more accurate, but shouldn't have much of a visible effect. Signed-off-by: Daniel Walker --- drivers/clocksource/acpi_pm.c | 5 ++++- include/linux/acpi_pmtmr.h | 5 +++-- include/linux/clocksource.h | 21 +++++++++++++++++++++ 3 files changed, 28 insertions(+), 3 deletions(-) Index: linux-2.6.25/drivers/clocksource/acpi_pm.c =================================================================== --- linux-2.6.25.orig/drivers/clocksource/acpi_pm.c +++ linux-2.6.25/drivers/clocksource/acpi_pm.c @@ -72,7 +72,7 @@ static struct clocksource clocksource_ac .read = acpi_pm_read, .mask = (cycle_t)ACPI_PM_MASK, .mult = 0, /*to be calculated*/ - .shift = 22, + .shift = 0, .flags = CLOCK_SOURCE_IS_CONTINUOUS, }; @@ -183,6 +183,9 @@ static int __init init_acpi_pm_clocksour if (!pmtmr_ioport) return -ENODEV; + clocksource_acpi_pm.shift = + clocksource_hz2shift(ACPI_PM_BITS, PMTMR_TICKS_PER_SEC); + clocksource_acpi_pm.mult = clocksource_hz2mult(PMTMR_TICKS_PER_SEC, clocksource_acpi_pm.shift); Index: linux-2.6.25/include/linux/acpi_pmtmr.h =================================================================== --- linux-2.6.25.orig/include/linux/acpi_pmtmr.h +++ linux-2.6.25/include/linux/acpi_pmtmr.h @@ -7,10 +7,11 @@ #define PMTMR_TICKS_PER_SEC 3579545 /* limit it to 24 bits */ -#define ACPI_PM_MASK CLOCKSOURCE_MASK(24) +#define ACPI_PM_BITS 24 +#define ACPI_PM_MASK CLOCKSOURCE_MASK(ACPI_PM_BITS) /* Overrun value */ -#define ACPI_PM_OVRRUN (1<<24) +#define ACPI_PM_OVRRUN (1 << ACPI_PM_BITS) #ifdef CONFIG_X86_PM_TIMER Index: linux-2.6.25/include/linux/clocksource.h =================================================================== --- linux-2.6.25.orig/include/linux/clocksource.h +++ linux-2.6.25/include/linux/clocksource.h @@ -157,6 +157,27 @@ static inline u32 clocksource_hz2mult(u3 } /** + * clocksource_hz2shift - calculates shift from hz and # of bits + * @bits: Number of bits this clocksource uses + * @hz: Clocksource frequency in Hz + * + * Helper functions that calculates the best shift value + * based on the hz and # of bits of any given clock. + */ +static inline u32 clocksource_hz2shift(u32 bits, u32 hz) +{ + u64 temp; + + for (; bits > 0; bits--) { + temp = (u64) NSEC_PER_SEC << bits; + do_div(temp, hz); + if ((temp >> 32) == 0) + break; + } + return bits; +} + +/** * clocksource_read: - Access the clocksource's current cycle value * @cs: pointer to clocksource being read * -- --