On Wed, Aug 3, 2011 at 6:56 AM, Kevin Hilman <khilman@xxxxxx> wrote: > 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> > > [...] > >> +int devfreq_update(struct device *dev) >> +{ >> + struct devfreq *devfreq; >> + int err = 0; >> + >> + mutex_lock(&devfreq_list_lock); >> + >> + devfreq = find_device_devfreq(dev); >> + if (IS_ERR(devfreq)) { >> + err = PTR_ERR(devfreq); >> + goto out; >> + } >> + >> + /* >> + * If the maximum frequency available is changed either by >> + * enabling higher frequency or disabling the current >> + * maximum frequency, we need to adjust the frequency >> + * (tickle) again if the device has been being tickled. >> + */ >> + if (devfreq->tickle) { >> + unsigned long freq = devfreq->profile->max_freq; >> + struct opp *opp = opp_find_freq_floor(devfreq->dev, &freq); >> + >> + if (IS_ERR(opp)) { >> + err = PTR_ERR(opp); >> + goto out; >> + } >> + >> + /* Max freq available is not changed */ >> + if (devfreq->previous_freq == freq) >> + goto out; >> + >> + /* Tickle again. Max freq available is changed */ >> + err = devfreq->profile->target(devfreq->dev, opp); >> + if (!err) >> + devfreq->previous_freq = freq; > > This looks an awful lot like _devfreq_tickle_device()... wondering why > that is not called here. > The device is already tickled by a user and we do not need to update the timing/delay information about the current tickle. We only need to adjust frequency in case the maximum available frequency has been changed. Anyway, in order to reduce redundant code, I will modify _devfreq_tickle_device to be able to be called by devfreq_update(). For now, if devfreq_update() uses _devfreq_tickle_device without modification, it will calculate num_tickle incorrectly and setting delay of _devfreq_tickle_device again is required. I will let _devfreq_tickle_device take delay = 0 for devfreq_update(). Thanks. - MyungJoo >> + } else { >> + /* Reevaluate the proper frequency */ >> + err = devfreq_do(devfreq); >> + } >> + >> +out: >> + mutex_unlock(&devfreq_list_lock); >> + return err; >> +} > > Kevin > _______________________________________________ > linux-pm mailing list > linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linux-foundation.org/mailman/listinfo/linux-pm > -- MyungJoo Ham (함명주), Ph.D. Mobile Software Platform Lab, Digital Media and Communications (DMC) Business Samsung Electronics cell: 82-10-6714-2858 _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
