Part 11: IIO, RTC, Regulator, Clock Drivers

This part covers four important kernel subsystems: Industrial I/O (IIO) for sensors and data acquisition, Real-Time Clock (RTC) for timekeeping, Regulator framework for power management, and Common Clock Framework (CCF) for clock providers.

flowchart TB
    subgraph Subsystems["Kernel Subsystems"]
        IIO["IIO<br/>Industrial I/O"]
        RTC["RTC<br/>Real-Time Clock"]
        REG["Regulator<br/>Framework"]
        CLK["Clock<br/>Framework"]
    end

    subgraph Devices["Device Types"]
        ADC["ADC/DAC"]
        ACCEL["Accelerometers"]
        GYRO["Gyroscopes"]
        RTCDEV["RTC Chips"]
        PMIC["PMICs"]
        LDO["LDOs/Bucks"]
        PLL["PLLs"]
        CLKGEN["Clock Generators"]
    end

    subgraph Consumers["Consumers"]
        APPS["Applications"]
        THERMAL["Thermal"]
        DRIVERS["Other Drivers"]
    end

    ADC --> IIO
    ACCEL --> IIO
    GYRO --> IIO
    RTCDEV --> RTC
    PMIC --> REG
    LDO --> REG
    PLL --> CLK
    CLKGEN --> CLK

    IIO --> APPS
    RTC --> APPS
    REG --> DRIVERS
    CLK --> DRIVERS

    style Subsystems fill:#738f99,stroke:#0277bd
    style Devices fill:#7a8f73,stroke:#2e7d32
    style Consumers fill:#8f8a73,stroke:#f9a825

What You’ll Learn

Industrial I/O (IIO)

IIO subsystem architecture
Channels, attributes, and buffers
Triggered buffer acquisition
IIO device registration

Real-Time Clock (RTC)

RTC subsystem overview
rtc_device implementation
Alarm and wake-up support
RTC class operations

Regulator Framework

Voltage regulator concepts
Provider (supply) drivers
Consumer API
Constraints and coupling

Common Clock Framework

Clock tree hierarchy
clk_hw implementation
Clock types (fixed, divider, mux, PLL)
Clock operations

Subsystem Overview

flowchart LR
    subgraph IIO_Sub["IIO Subsystem"]
        IIODEV["iio_dev"]
        IIOCHAN["iio_chan_spec"]
        IIOBUF["IIO Buffer"]
        IIOTRIG["IIO Trigger"]
    end

    subgraph RTC_Sub["RTC Subsystem"]
        RTCDEV2["rtc_device"]
        RTCOPS["rtc_class_ops"]
        RTCALARM["Alarms"]
    end

    subgraph REG_Sub["Regulator Framework"]
        REGDEV["regulator_dev"]
        REGDESC["regulator_desc"]
        REGCON["regulator_consumer"]
    end

    subgraph CLK_Sub["Clock Framework"]
        CLKHW["clk_hw"]
        CLKOPS["clk_ops"]
        CLKPROV["Clock Provider"]
    end

    style IIO_Sub fill:#738f99,stroke:#0277bd
    style RTC_Sub fill:#7a8f73,stroke:#2e7d32
    style REG_Sub fill:#8f8a73,stroke:#f9a825
    style CLK_Sub fill:#8f6d72,stroke:#c62828

Key Structures

Subsystem	Main Structure	Registration Function
IIO	`struct iio_dev`	`devm_iio_device_register()`
RTC	`struct rtc_device`	`devm_rtc_device_register()`
Regulator	`struct regulator_dev`	`devm_regulator_register()`
Clock	`struct clk_hw`	`devm_clk_hw_register()`

Common Patterns

These subsystems share several design patterns:

Provider/Consumer Model: Drivers expose resources; others consume them
Hierarchical Organization: Clocks in trees, regulators in supplies
Device Tree Integration: Standard bindings for configuration
Managed Resources: devm_* functions for automatic cleanup
Runtime PM Integration: Power-aware operation

In This Part

IIO Subsystem - IIO architecture overview
IIO Driver - Implementing iio_dev
IIO Buffers - Triggered buffer acquisition
RTC Subsystem - RTC architecture
RTC Driver - Implementing rtc_device
Regulator Subsystem - Regulator framework
Regulator Driver - Provider/consumer implementation
Clock Framework - CCF overview
Clock Provider - Implementing clk_hw

Prerequisites

Before starting this part, you should understand:

Platform drivers and Device Tree (Part 8)
I2C/SPI drivers (Part 9)
Managed resources (devm_*) - essential for these drivers
Basic kernel memory management (Part 5)