Date: Fri, 18 Nov 2016 13:17:41 +0000
From: Lee Jones <lee.jones@linaro.org>
To: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>, Kukjin Kim <kgene@kernel.org>,
        Javier Martinez Canillas <javier@osg.samsung.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ben Dooks <ben.dooks@codethink.co.uk>, Arnd Bergmann <arnd@arndb.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Sylwester Nawrocki <s.nawrocki@samsung.com>,
        Tomasz Figa <tomasz.figa@gmail.com>
Subject: Re: [PATCH v2] ARM: Drop fixed 200 Hz timer requirement from Samsung
 platforms
Message-ID: <20161118131741.GB2301@dell.home>
References: <1479453418-25314-1-git-send-email-krzk@kernel.org>
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On Fri, 18 Nov 2016, Krzysztof Kozlowski 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@linaro.org>

Acked-by: Lee Jones <lee.jones@linaro.org>

> [Dropping 200_HZ from S3C/S5P suggested by Arnd]
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
> Cc: Kukjin Kim <kgene@kernel.org>
> Tested-by: Javier Martinez Canillas <javier@osg.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
>  

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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