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Diffstat (limited to 'ARM-Drop-fixed-200-Hz-timer-requirement-from-Samsung-platforms.patch')
| -rw-r--r-- | ARM-Drop-fixed-200-Hz-timer-requirement-from-Samsung-platforms.patch | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/ARM-Drop-fixed-200-Hz-timer-requirement-from-Samsung-platforms.patch b/ARM-Drop-fixed-200-Hz-timer-requirement-from-Samsung-platforms.patch new file mode 100644 index 000000000..bf389545b --- /dev/null +++ b/ARM-Drop-fixed-200-Hz-timer-requirement-from-Samsung-platforms.patch @@ -0,0 +1,88 @@ +From patchwork Fri Nov 18 11:15:12 2016 +Content-Type: text/plain; charset="utf-8" +MIME-Version: 1.0 +Content-Transfer-Encoding: 7bit +Subject: [v3] ARM: Drop fixed 200 Hz timer requirement from Samsung platforms +From: Krzysztof Kozlowski <krzk@kernel.org> +X-Patchwork-Id: 9436225 +Message-Id: <1479467712-5218-1-git-send-email-krzk@kernel.org> +To: Russell King <linux@armlinux.org.uk>, Kukjin Kim <kgene@kernel.org>, + Krzysztof Kozlowski <krzk@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 +Cc: Arnd Bergmann <arnd@arndb.de>, + Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, + Tomasz Figa <tomasz.figa@gmail.com>, + Ben Dooks <ben.dooks@codethink.co.uk>, + Sylwester Nawrocki <s.nawrocki@samsung.com>, + Lee Jones <lee.jones@linaro.org>, + Marek Szyprowski <m.szyprowski@samsung.com> +Date: Fri, 18 Nov 2016 13:15:12 +0200 + +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 <lee.jones@linaro.org> +[Dropping of 200_HZ from S3C/S5P was 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 on Exynos5800] +Tested-by: Javier Martinez Canillas <javier@osg.samsung.com> +Acked-by: Kukjin Kim <kgene@kernel.org> +[Tested on S3C2440] +Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com> +--- + +Changes since v2: +1. Extend message. +2. Add Kukjin's ack. +3. Add Sylwester's tested-by. + +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 + |