Commit:     5248c657898c018bcd23ef77759fa1d6c690bdf4
Parent:     156864f806baa4e1aa6eabd28ac45ecc92b31315
Author:     David Brownell <[EMAIL PROTECTED]>
AuthorDate: Mon Nov 12 17:59:10 2007 +0100
Committer:  Russell King <[EMAIL PROTECTED]>
CommitDate: Sat Jan 26 15:00:31 2008 +0000

    [ARM] 4646/1: AT91: configurable HZ, default to 128
    This makes HZ configurable on AT91, following the model used on OMAP.
    It defaults to a power of two on AT91rm9200 chips, avoiding rounding
    errors which come from dividing a 32 KiHz clock to generate scheduler
    irqs; and uses 100 on AT91sam926x chips, using MCK/16 (multi-MHZ).
    Signed-off-by: David Brownell <[EMAIL PROTECTED]>
    Acked-by: Remy Bhmer <[EMAIL PROTECTED]>
    Acked-by: Andrew Victor <[EMAIL PROTECTED]>
    Signed-off-by: Russell King <[EMAIL PROTECTED]>
 arch/arm/Kconfig           |    1 +
 arch/arm/mach-at91/Kconfig |   16 ++++++++++++++++
 2 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a04f507..93e40b6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -657,6 +657,7 @@ config HZ
        default 128 if ARCH_L7200
        default 200 if ARCH_EBSA110 || ARCH_S3C2410
        default OMAP_32K_TIMER_HZ if ARCH_OMAP && OMAP_32K_TIMER
+       default AT91_TIMER_HZ if ARCH_AT91
        default 100
 config AEABI
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index 05a9f8a..214733e 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -219,6 +219,22 @@ config AT91_PROGRAMMABLE_CLOCKS
          Select this if you need to program one or more of the PCK0..PCK3
          programmable clock outputs.
+config AT91_TIMER_HZ
+       int "Kernel HZ (jiffies per second)"
+       range 32 1024
+       depends on ARCH_AT91
+       default "128" if ARCH_AT91RM9200
+       default "100"
+       help
+         On AT91rm9200 chips where you're using a system clock derived
+         from the 32768 Hz hardware clock, this tick rate should divide
+         it exactly: use a power-of-two value, such as 128 or 256, to
+         reduce timing errors caused by rounding.
+         On AT91sam926x chips, or otherwise when using a higher precision
+         system clock (of at least several MHz), rounding is less of a
+         problem so it can be safer to use a decimal values like 100.
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