From da6b21e97e39d42f90ab490ce7b54a0fe2c3fe35 Mon Sep 17 00:00:00 2001 From: Krzysztof Kozlowski Date: Fri, 18 Nov 2016 13:15:12 +0200 Subject: ARM: Drop fixed 200 Hz timer requirement from Samsung platforms All Samsung platforms, including the Exynos, are selecting HZ_FIXED with 200 Hz. Unfortunately in case of multiplatform image this affects also other platforms when Exynos is enabled. This looks like an very old legacy code, dating back to initial upstreaming of S3C24xx. Probably it was required for s3c24xx timer driver, which was removed in commit ad38bdd15d5b ("ARM: SAMSUNG: Remove unused plat-samsung/time.c"). Since then, this fixed 200 Hz spread everywhere, including out-of-tree Samsung kernels (SoC vendor's and Tizen's). I believe this choice was rather an effect of coincidence instead of conscious choice. On S3C24xx, the PWM counter is only 16 bit wide, and with the typical 12MHz input clock that overflows every 5.5ms. This works with HZ=200 or higher but not with HZ=100 which needs a 10ms interval between ticks. On Later chips (S3C64xx, S5P and EXYNOS), the counter is 32 bits and does not have this problem. The new samsung_pwm_timer driver solves the problem by scaling the input clock by a factor of 50 on S3C24xx, which makes it less accurate but allows HZ=100 as well as CONFIG_NO_HZ with fewer wakeups. Few perf mem and sched tests on Odroid XU3 board (Exynos5422, 4x Cortex A7, 4x Cortex A15) show no regressions when switching from 200 Hz to other values. Reported-by: Lee Jones [Dropping of 200_HZ from S3C/S5P was suggested by Arnd] Reported-by: Arnd Bergmann Cc: Kukjin Kim Signed-off-by: Krzysztof Kozlowski [Tested on Exynos5800] Tested-by: Javier Martinez Canillas Acked-by: Kukjin Kim [Tested on S3C2440] Tested-by: Sylwester Nawrocki Acked-by: Lee Jones --- arch/arm/Kconfig | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/arm') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index b5d529fdffab..ced2e08a9d08 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1496,8 +1496,7 @@ source kernel/Kconfig.preempt config HZ_FIXED int - default 200 if ARCH_EBSA110 || ARCH_S3C24XX || \ - ARCH_S5PV210 || ARCH_EXYNOS4 + default 200 if ARCH_EBSA110 default 128 if SOC_AT91RM9200 default 0 -- cgit v1.2.3