ARM: 6277/1: mach-shmobile: Allow users to select HZ, default to 128

Introduce SHMOBILE_TIMER_HZ for SH-Mobile.

Allow users to select HZ on their system to
minimize potential timer drift. Use 128 Hz as
default to work well with the 32768 Hz RCLK.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig

@@ -1189,6 +1189,7 @@ config HZ
 	default 200 if ARCH_EBSA110 || ARCH_S3C2410 || ARCH_S5P6440 || ARCH_S5P6442 || ARCH_S5PV210
 	default OMAP_32K_TIMER_HZ if ARCH_OMAP && OMAP_32K_TIMER
 	default AT91_TIMER_HZ if ARCH_AT91
+	default SHMOBILE_TIMER_HZ if ARCH_SHMOBILE
 	default 100
 
 config THUMB2_KERNEL

arch/arm/mach-shmobile/Kconfig

@@ -70,6 +70,18 @@ endmenu
 
 menu "Timer and clock configuration"
 
+config SHMOBILE_TIMER_HZ
+	int "Kernel HZ (jiffies per second)"
+	range 32 1024
+	default "128"
+	help
+	  Allows the configuration of the timer frequency. It is customary
+	  to have the timer interrupt run at 1000 Hz or 100 Hz, but in the
+	  case of low timer frequencies other values may be more suitable.
+	  SH-Mobile systems using a 32768 Hz RCLK for clock events may want
+	  to select a HZ value such as 128 that can evenly divide RCLK.
+	  A HZ value that does not divide evenly may cause timer drift.
+
 config SH_TIMER_CMT
 	bool "CMT timer driver"
 	default y