MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx> writes: > With OPPs, a device may have multiple operable frequency and voltage > sets. However, there can be multiple possible operable sets and a system > will need to choose one from them. In order to reduce the power > consumption (by reducing frequency and voltage) without affecting the > performance too much, a Dynamic Voltage and Frequency Scaling (DVFS) > scheme may be used. > > This patch introduces the DVFS capability to non-CPU devices with OPPs. > DVFS is a techique whereby the frequency and supplied voltage of a > device is adjusted on-the-fly. DVFS usually sets the frequency as low > as possible with given conditions (such as QoS assurance) and adjusts > voltage according to the chosen frequency in order to reduce power > consumption and heat dissipation. > > The generic DVFS for devices, DEVFREQ, may appear quite similar with > /drivers/cpufreq. However, CPUFREQ does not allow to have multiple > devices registered and is not suitable to have multiple heterogenous > devices with different (but simple) governors. > > Normally, DVFS mechanism controls frequency based on the demand for > the device, and then, chooses voltage based on the chosen frequency. > DEVFREQ also controls the frequency based on the governor's frequency > recommendation and let OPP pick up the pair of frequency and voltage > based on the recommended frequency. Then, the chosen OPP is passed to > device driver's "target" callback. > > Tested with memory bus of Exynos4-NURI board. > > The test code with board support for Exynos4-NURI is at > http://git.infradead.org/users/kmpark/linux-2.6-samsung/shortlog/refs/heads/devfreq > > Signed-off-by: MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx> > Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > -- > Thank you for your valuable comments, Rafael, Greg, Pavel, and Colin. > > Changed from v3 > - In kerneldoc comments, DEVFREQ has ben replaced by devfreq FYI... there are still lots of kerneldoc comments in this version with DEVFREQ instead of devfreq, particularily in devfreq.h. Kevin _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
