Re: [RFC PATCHv3 1/7] devfreq: event: Add new devfreq_event class to provide basic data for devfreq governor
From: Krzysztof Kozlowski
Date: Mon Dec 15 2014 - 09:53:19 EST
On piÄ, 2014-12-12 at 17:27 +0900, Chanwoo Choi wrote:
> This patch add new devfreq_event class for devfreq_event device which provide
> raw data (e.g., memory bus utilization/GPU utilization). This raw data from
> devfreq_event data would be used for the governor of devfreq subsystem.
> - devfreq_event device : Provide raw data for governor of existing devfreq device
> - devfreq device : Monitor device state and change frequency/voltage of device
> using the raw data from devfreq_event device
> The devfreq subsystem support generic DVFS(Dynamic Voltage/Frequency Scaling)
> for Non-CPU Devices. The devfreq device would dertermine current device state
> using various governor (e.g., ondemand, performance, powersave). After completed
> determination of system state, devfreq device would change the frequency/voltage
> of devfreq device according to the result of governor.
> But, devfreq governor must need basic data which indicates current device state.
> Existing devfreq subsystem only consider devfreq device which check current system
> state and determine proper system state using basic data. There is no subsystem
> for device providing basic data to devfreq device.
> The devfreq subsystem must need devfreq_event device(data-provider device) for
> existing devfreq device. So, this patch add new devfreq_event class for
> devfreq_event device which read various basic data(e.g, memory bus utilization,
> GPU utilization) and provide measured data to existing devfreq device through
> standard APIs of devfreq_event class.
> The following description explains the feature of two kind of devfreq class:
> - devfreq class (existing)
> : devfreq consumer device use raw data from devfreq_event device for
> determining proper current system state and change voltage/frequency
> dynamically using various governors.
> - devfreq_event class (new)
> : Provide measured raw data to devfreq device for governor
> Cc: MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx>
> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> Signed-off-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
> + * devfreq_event_get_event() - Get event and total_event from devfreq-event dev.
> + * @edev : the devfreq-event device
> + *
> + * Note that this function get the calculated event data from devfreq-event dev
> + * after stoping the progress of whole sequence of devfreq-event dev. Return
> + * current event data and total_event should be stored in second parameter
> + * (total_event).
> + */
> +u64 devfreq_event_get_event(struct devfreq_event_dev *edev, u64 *total_event)
I think this function should return int (0 for success, negative
otherwise) and store the "event" under pointer passed as argument.
1. error conditions are indicated with 'return 0' but should be 'return
2. Exynos-ppmu driver returns -EINVAL.
Checking for error conditions is in such case more complex than it
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