feat(dvfs): update Dvfs trait

[ytakano]

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Notes for reviewers

[ytakano]

@atsushi421

I added four methods to Dvfs.

• set_min_performance(min: u8) -> bool
• get_min_performance() -> Option<u8>
• set_max_performance(max: u8) -> bool
• get_max_performance() -> Option<u8>

Additionally, update the return value of convention methods to return bool or Option<u64>.
What do you think?

pub trait Dvfs {
    /// Fix the frequency of the current CPU.
    ///
    /// If current driver does not support this operation,
    /// it will return `false`.
    fn fix_freq(freq: u64) -> bool {
        false
    }

    /// Get the maximum frequency of the current CPU.
    ///
    /// If current driver does not support this operation,
    /// it will return `None`.
    fn get_max_freq() -> Option<u64> {
        None
    }

    /// Get the frequency of the current CPU.
    ///
    /// If current driver does not support this operation,
    /// it will return `None`.
    fn get_curr_freq() -> Option<u64> {
        None
    }

    /// Select the Minimum Performance.
    /// (range from 0, lowest performant, through 100, highest performance)
    ///
    /// If current driver does not support this operation,
    /// it will return `false`.
    fn set_min_performance(min: u8) -> bool {
        false
    }

    /// Get the Minimum Performance.
    /// (range from 0, lowest performant, through 100, highest performance)
    ///
    /// If current driver does not support this operation,
    /// it will return `None`.
    fn get_min_performance() -> Option<u8> {
        None
    }

    /// Set the Maximum Performance.
    /// (range from 0, lowest performant, through 100, highest performance)
    ///
    /// If current driver does not support this operation,
    /// it will return `false`.
    fn set_max_performance(max: u8) -> bool {
        false
    }

    /// Get the Maximum Performance.
    /// (range from 0, lowest performant, through 100, highest performance)
    ///
    /// If current driver does not support this operation,
    /// it will return `None`.
    fn get_max_performance() -> Option<u8> {
        None
    }
}

[atsushi421]

@ytakano
I have no concerns, thank you.

[ytakano]

Add set_min_max_performance() to select the minimum and maximum Performance.

pub trait Dvfs {
    fn set_min_max_performance();
}