linux-kernel - Re: [PATCH v2] ARM: Drop fixed 200 Hz timer requirement from Samsung platforms

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Date:   Fri, 18 Nov 2016 16:57:40 +0900
From:   Kukjin Kim <kgene.kim@...il.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Kukjin Kim <kgene@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        Lee Jones <lee.jones@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>
Subject: Re: [PATCH v2] ARM: Drop fixed 200 Hz timer requirement from Samsung platforms

2016. 11. 18. 16:16 Krzysztof Kozlowski <krzk@...nel.org> wrote:

> 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.
> 
> Exynos uses its own MCT or arch timer and can work with all HZ values.
> Older platforms use newer Samsung PWM timer driver which should handle
> down to 100 Hz.
> 
> 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 <lee.jones@...aro.org>
> [Dropping 200_HZ from S3C/S5P suggested by Arnd]
> Reported-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> Cc: Kukjin Kim <kgene@...nel.org>

Acked-by: Kukjin Kim <kgene@...nel.org>

> Tested-by: Javier Martinez Canillas <javier@....samsung.com>
> 
> ---
> 
> Tested on Exynos5422 and Exynos5800 (by Javier). It would be
> appreciated if anyone could test it on S3C24xx or S5PV210.
> 
> Changes since v1:
> 1. Add Javier's tested-by.
> 2. Drop HZ_FIXED also from ARCH_S5PV210 and ARCH_S3C24XX after Arnd
>   suggestions and analysis.
> ---
> arch/arm/Kconfig | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
> 
> 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
> 
> -- 
> 2.7.4
>