For a usage example, please look at http://git.infradead.org/users/kmpark/linux-2.6-samsung/shortlog/refs/heads/devfreq In the above git tree, DVFS (dynamic voltage and frequency scaling) mechanism is applied to the memory bus of Exynos4210 for Exynos4210-NURI boards. In the example, the LPDDR2 DRAM frequency changes between 133, 266, and 400MHz and other related clocks simply follow the determined DDR RAM clock. The DEVFREQ driver for Exynos4210 memory bus is at /arch/arm/mach-exynos4/devfreq_bus.c in the git tree. In the dd (writing and reading 360MiB) test with NURI board, the memory throughput was not changed (the performance is not deteriorated) while the SoC power consumption has been reduced by 1%. When the memory access is not that intense while the CPU is heavily used, the SoC power consumption has been reduced by 6%. The power consumption has been compared with the case using the conventional Exynos4210 CPUFREQ driver, which sets memory bus frequency according to the CPU core frequency. Besides, when the CPU core running slow and the memory access is intense, the performance (memory throughput) has been increased by 11% (with higher SoC power consumption of 5%). The tested governor is "simple-ondemand". MyungJoo Ham (3): PM: Introduce DEVFREQ: generic DVFS framework with device-specific OPPs PM / DEVFREQ: add basic governors PM / DEVFREQ: add sysfs interface Documentation/ABI/testing/sysfs-devices-power | 45 ++ drivers/base/power/Makefile | 1 + drivers/base/power/devfreq.c | 555 +++++++++++++++++++++++++ drivers/base/power/opp.c | 9 + include/linux/devfreq.h | 111 +++++ kernel/power/Kconfig | 34 ++ 6 files changed, 755 insertions(+), 0 deletions(-) create mode 100644 drivers/base/power/devfreq.c create mode 100644 include/linux/devfreq.h -- 1.7.4.1 _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
