lkml.org 
[lkml]   [2008]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] clocksource: shift helper
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 <dwalker@mvista.com>

---
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
*
--
--


\
 
 \ /
  Last update: 2008-05-01 19:37    [from the cache]
©2003-2011 Jasper Spaans