Linux pinctrl子系统概念介绍和LED驱动示例

Linux pinctrl子系统介绍

在很多SOC内部都有pin的控制器，通过配置pin控制器，可以将引脚配置为特定的功能特性，在软件方面，linux内核提供pinctrl子系统，目的为了统一soc厂商的pin脚管理。

以NXP i.MX7D为例，每个IO引脚有多达8种的复用功能，具体用哪一种功能，通过IOMUXC来配置引脚的具体特性。

Linux pinctrl的处理工作

引脚复用

在Linux内核DT文件夹中arch/arm/boot/dts/imx7d-pinfunc.h的文件中，定义了所有引脚的复用配置。以下面的为例

#define MX7D_PAD_I2C1_SDA_GPIO4_IO9   0x014c 0x03BC 0x0000 0x5 0x0

• 0x014c是IOMUXC_SW_MUX_CTL_PAD_I2C1_SDA多路复用寄存器的偏移量

• 0x03BC是IOMUXC_SW_PAD_CTL_PAD_I2C1_SDA控制寄存器的偏移量

• 0x5 是IOMUXC_SW_MUX_CTL_PAD_I2C1_SDA多路复用寄存器ALT5的模式，也就当做普通的GPIO来用

引脚配置

引脚的具体配置，从linux3.x内核后都是在设备树中进行具体的复用和配置。

以ledclassRGB节点为例,此节点对应的IO配置为pinctrl_gpio_leds、pinctrl_gpio_led，其中pinctrl_gpio_leds主要对MX7D_PAD_SAI2_TX_BCLK__GPIO6_IO20、MX7D_PAD_SAI2_RX_DATA__GPIO6_IO21引脚进行复用，最后的0x11是配置前面控制寄存器的值

0x11

mux_reg：复用配置寄存器偏移地址
conf_reg：引脚配置寄存器偏移地址
input_reg：输入配置寄存器偏移地址
mux_mode：复用配置寄存器值
input_val：输入配置寄存器值

ledclassRGB {
        compatible = "arrow,RGBclassleds";
        reg = <0x30200000 0x60000>;    
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_gpio_leds &pinctrl_gpio_led>;

        red {
            label = "red";
        };

        green {
            label = "green";
        };

        blue {
            label = "blue";
            linux,default-trigger = "heartbeat";
        };
    };

pinctrl_gpio_leds: pinctrl_gpio_leds_grp {

            fsl,pins = <
                MX7D_PAD_SAI2_TX_BCLK__GPIO6_IO20    0x11
                MX7D_PAD_SAI2_RX_DATA__GPIO6_IO21    0x11
            >;
  };

MMIO(内存映射IO)设备访问

对外围设备的控制是通过写入及读取其寄存器来实现的，通过内存地址空间（MMIO）或地址空间（PIO）的连续地址来访问这些寄存器的

1：MMIO

主存和IO设备使用相同的总线地址

使用常规指令访问IO设备

linux支持的不同体系结构中使用广泛的IO方法

2：PIO

主存和IO设备使用不同的地址空间

使用特殊的CPU指令来访问IO设备

x86上的示例：IN和OUT指令

i.MX7D使用的是MMIO，但是驱动程序中无法直接访问物理地址，需要MMU进行映射。

可以通过下面的函数

1：使用ioremap、iounmap

2: 使用devm_ioremap、devm_iounmap

3：ioread8\ioread16 iowrite8\iowrite16

LED驱动示例：

#include 
#include 
#include 
#include 
#include 
#include 

#define GPDAT1_offset        0x00
#define GPDIR1_offset        0x04
#define GPDAT6_offset        0x50000
#define GPDIR6_offset        0x50004

#define GPIO1_DIR_MASK 1 << 2
#define GPIO1_DATA_MASK 1 << 2

#define GPIO6_DIR_MASK (1 << 20 | 1 << 21)
#define GPIO6_DATA_MASK (1 << 20 | 1 << 21)

#define LED_RED_MASK 1 << 2
#define LED_GREEN_MASK 1 << 20
#define LED_BLUE_MASK 1 << 21


struct led_dev
{
    u32 led_mask; /* different mask if led is R,G or B */
    void __iomem *base;
    struct led_classdev cdev;
};

static void led_control(struct led_classdev *led_cdev, enum led_brightness b)
{
    u32 read, write;
    struct led_dev *led = container_of(led_cdev, struct led_dev, cdev);

    if (b != LED_OFF) { /* LED ON */

        if (led->led_mask == LED_RED_MASK) {
            read = ioread32(led->base + GPDAT1_offset);
            write = read | led->led_mask;
            iowrite32(write, led->base + GPDAT1_offset);
        }
        if ((led->led_mask == LED_GREEN_MASK) || (led->led_mask == LED_BLUE_MASK)) {
            read = ioread32(led->base + GPDAT6_offset);
            write = read | led->led_mask;
            iowrite32(write, led->base + GPDAT6_offset);
        }
    }
        
    else {
            
        if (led->led_mask == LED_RED_MASK) {
            read = ioread32(led->base + GPDAT1_offset);
            write = read & ~(led->led_mask);
            iowrite32(write, led->base + GPDAT1_offset);
        }
        if ((led->led_mask == LED_GREEN_MASK) || (led->led_mask == LED_BLUE_MASK)) {
            read = ioread32(led->base + GPDAT6_offset);
            write = read & ~(led->led_mask);
            iowrite32(write, led->base + GPDAT6_offset);
        }
    }
}

static int __init ledclass_probe(struct platform_device *pdev)
{

    u32 GPDIR1_read, GPDIR1_write;
    u32 GPDIR6_read, GPDIR6_write;
    u32 GPDAT1_read, GPDAT1_write;
    u32 GPDAT6_read, GPDAT6_write;
    void __iomem *g_ioremap_addr;
    struct device_node *child;
    struct resource *r;
    struct device *dev = &pdev->dev;
    int count, ret;

    dev_info(dev, "platform_probe enter\n");

    /* get our first memory resource from device tree */
    r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (!r) {
        dev_err(dev, "IORESOURCE_MEM, 0 does not exist\n");
        return -EINVAL;
    }
    dev_info(dev, "r->start = 0x%08lx\n", (long unsigned int)r->start);
    dev_info(dev, "r->end = 0x%08lx\n", (long unsigned int)r->end);

    /* ioremap our memory region */
    g_ioremap_addr = devm_ioremap(dev, r->start, resource_size(r));
    if (!g_ioremap_addr) {
        dev_err(dev, "ioremap failed \n");
        return -ENOMEM;
    }

    count = of_get_child_count(dev->of_node);
    if (!count)
        return -EINVAL;

    dev_info(dev, "there are %d nodes\n", count);


    /* Set GPIO1_IO_2 direction bit to output */
    GPDIR1_read = ioread32(g_ioremap_addr + GPDIR1_offset);
    GPDIR1_write = GPDIR1_read | (GPIO1_DIR_MASK);
    iowrite32(GPDIR1_write, g_ioremap_addr + GPDIR1_offset);
    
    GPDIR6_read = ioread32(g_ioremap_addr + GPDIR6_offset);
    GPDIR6_write = GPDIR6_read | (GPIO6_DIR_MASK);
    iowrite32(GPDIR6_write, g_ioremap_addr + GPDIR6_offset);

    /* set all leds to 0 output */
    GPDAT1_read = ioread32(g_ioremap_addr + GPDAT1_offset);
    GPDAT1_write = GPDAT1_read & ~(GPIO1_DATA_MASK);
    iowrite32(GPDAT1_write, g_ioremap_addr + GPDAT1_offset);
    GPDAT6_read = ioread32(g_ioremap_addr + GPDAT6_offset);
    GPDAT6_write = GPDAT6_read & ~(GPIO6_DATA_MASK);
    iowrite32(GPDAT6_write, g_ioremap_addr + GPDAT6_offset);

    for_each_child_of_node(dev->of_node, child){

        struct led_dev *led_device;
        struct led_classdev *cdev;
        led_device = devm_kzalloc(dev, sizeof(*led_device), GFP_KERNEL);
        if (!led_device)
            return -ENOMEM;

        cdev = &led_device->cdev;

        led_device->base = g_ioremap_addr;

        of_property_read_string(child, "label", &cdev->name);

        if (strcmp(cdev->name,"red") == 0) {
            led_device->led_mask = LED_RED_MASK;
            led_device->cdev.default_trigger = "heartbeat";
        }
        else if (strcmp(cdev->name,"green") == 0) {
            led_device->led_mask = LED_GREEN_MASK;
        }
        else if (strcmp(cdev->name,"blue") == 0) {
            led_device->led_mask = LED_BLUE_MASK;
        }
        else {
            dev_info(dev, "Bad device tree value\n");
            return -EINVAL;
        }

        /* Disable timer trigger until led is on */
        led_device->cdev.brightness = LED_OFF;
        led_device->cdev.brightness_set = led_control;

        ret = devm_led_classdev_register(dev, &led_device->cdev);
        if (ret) {
            dev_err(dev, "failed to register the led %s\n", cdev->name);
            of_node_put(child);
            return ret;
        }
    }
    
    dev_info(dev, "leds_probe exit\n");

    return 0;
}

static int __exit ledclass_remove(struct platform_device *pdev)
{
    dev_info(&pdev->dev, "leds_remove enter\n");

    dev_info(&pdev->dev, "leds_remove exit\n");

    return 0;
}

static const struct of_device_id my_of_ids[] = {
    { .compatible = "arrow,RGBclassleds"},
    {},
};

MODULE_DEVICE_TABLE(of, my_of_ids);

static struct platform_driver led_platform_driver = {
    .probe = ledclass_probe,
    .remove = ledclass_remove,
    .driver = {
        .name = "RGBclassleds",
        .of_match_table = my_of_ids,
        .owner = THIS_MODULE,
    }
};

static int ledRGBclass_init(void)
{
    int ret_val;
    pr_info("demo_init enter\n");

    ret_val = platform_driver_register(&led_platform_driver);
    if (ret_val !=0)
    {
        pr_err("platform value returned %d\n", ret_val);
        return ret_val;

    }

    pr_info("demo_init exit\n");
    return 0;
}

static void ledRGBclass_exit(void)
{
    pr_info("led driver enter\n");

    platform_driver_unregister(&led_platform_driver);

    pr_info("led driver exit\n");
}

module_init(ledRGBclass_init);
module_exit(ledRGBclass_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alberto Liberal ");
MODULE_DESCRIPTION("This is a driver that turns on/off RGB leds \
           using the LED subsystem");