a3c98b8b2e
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. When PM QoS is going to be used with the devfreq device, the device driver should enable OPPs that are appropriate with the current PM QoS requests. In order to do so, the device driver may call opp_enable and opp_disable at the notifier callback of PM QoS so that PM QoS's update_target() call enables the appropriate OPPs. Note that at least one of OPPs should be enabled at any time; be careful when there is a transition. Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> Reviewed-by: Mike Turquette <mturquette@ti.com> Acked-by: Kevin Hilman <khilman@ti.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
40 lines
1.5 KiB
Plaintext
40 lines
1.5 KiB
Plaintext
config ARCH_HAS_DEVFREQ
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bool
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depends on ARCH_HAS_OPP
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help
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Denotes that the architecture supports DEVFREQ. If the architecture
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supports multiple OPP entries per device and the frequency of the
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devices with OPPs may be altered dynamically, the architecture
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supports DEVFREQ.
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menuconfig PM_DEVFREQ
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bool "Generic Dynamic Voltage and Frequency Scaling (DVFS) support"
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depends on PM_OPP && ARCH_HAS_DEVFREQ
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help
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With OPP support, a device may have a list of frequencies and
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voltages available. DEVFREQ, a generic DVFS framework can be
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registered for a device with OPP support in order to let the
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governor provided to DEVFREQ choose an operating frequency
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based on the OPP's list and the policy given with DEVFREQ.
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Each device may have its own governor and policy. DEVFREQ can
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reevaluate the device state periodically and/or based on the
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OPP list changes (each frequency/voltage pair in OPP may be
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disabled or enabled).
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Like some CPUs with CPUFREQ, a device may have multiple clocks.
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However, because the clock frequencies of a single device are
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determined by the single device's state, an instance of DEVFREQ
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is attached to a single device and returns a "representative"
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clock frequency from the OPP of the device, which is also attached
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to a device by 1-to-1. The device registering DEVFREQ takes the
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responsiblity to "interpret" the frequency listed in OPP and
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to set its every clock accordingly with the "target" callback
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given to DEVFREQ.
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if PM_DEVFREQ
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comment "DEVFREQ Drivers"
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endif # PM_DEVFREQ
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