[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 <dbrownell@users.sourceforge.net>
Acked-by: Remy Bhmer <linux@bohmer.net>
Acked-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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 @@
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 @@
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.
+
endmenu
endif