開發板：tiny4412SDK + S702 + 4GB Flash
要移植的核心版本：Linux-4.4.0 （支援device tree）
u-boot版本：友善之臂自帶的 U-Boot 2010.12
busybox版本：busybox 1.25

目標：
由於 tiny4412 的lcd背光控制採用的一線觸控，並不開源，因此移植友善自帶的linux3.5 核心中的背光相關部分驅動程式。

原理圖：

裝置樹：

        [email protected]{
                compatible         = "tiny4412,backlight_demo";
                reg = <
 
0x139D00000x14>;
                tiny4412,backlight = <&gpx12GPIO_ACTIVE_HIGH>;
                pinctrl-names = "backlight_out","backlight_in";
                pinctrl-0 = <&backlight_out>;
                pinctrl-1 = <&backlight_in>;
                interrupts = <0400>;
                clocks = <
 
&clockCLK_PWM>;
                clock-names = "timers";
        };

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&pinctrl_1 {
        backlight_out: backlight_out{
                samsung,pins = "gpx1-2";
                samsung,pin-function = <1>;
                samsung,pin-pud = <0>;
                samsung,pin-drv
 
 = <0>;
        };
         backlight_in: backlight_in{
                samsung,pins = "gpx1-2";
                samsung,pin-function = <0>;
                samsung,pin-pud = <0>;
                samsung,pin-drv = <0>;
        };
};

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程式碼：

//參考友善自帶的 Tiny4412_1wire_host.c                                                                                 
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/platform_device.h>
#include <linux/gpio.h>
#include <linux/of.h>
#include <linux/of_gpio.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <linux/bitops.h>
#include <linux/clk.h>
#include <linux/export.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/pwm.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/time.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
/*
    PWM 時鐘頻率 100M
    100M / 250 / 4 = 100000
    1/100000 = 10us
*/

static int              major;
static struct   cdev    backlight_cdev;
static struct   class   *cls;
static struct pinctrl   *pctrl;
static struct pinctrl_state *pstate_in;
static struct pinctrl_state *pstate_out;
static int              one_write_pin;

struct TIMER_BASE
{
    unsigned int TCFG0;
    unsigned int TCFG1;
    unsigned int TCON;
    unsigned int TCNTB0;
    unsigned int TCMPB0;
    unsigned int TCNTO0;
    unsigned int TCNTB1;
    unsigned int TCMPB1;
    unsigned int TCNTO1;
    unsigned int TCNTB2;
    unsigned int TCMPB2;
    unsigned int TCNTO2;
    unsigned int TCNTB3;
    unsigned int TCMPB3;
    unsigned int TCNTO3;
    unsigned int TCNTB4;
    unsigned int TCBTO4;
    unsigned int TINT_CSTAT;
};

volatile static struct TIMER_BASE *timer = NULL;

static volatile unsigned int io_bit_count;
static volatile unsigned int io_data;

enum
{
    IDLE,
    START,
    REQUEST,
    WAITING,
    RESPONSE,
    STOPING,
} one_wire_status = IDLE;

static inline void stop_timer_for_1wire(void)
{
    unsigned long tcon;
    tcon = timer->TCON;
    tcon &= ~(1 << 16);
    timer->TCON = tcon;
}

static irqreturn_t timer_for_1wire_interrupt(int irq, void *dev_id)
{
    unsigned int tint;
    tint = timer->TINT_CSTAT;
    tint |= 0x100;
    timer->TINT_CSTAT = tint;
    //printk("timer_for_1wire_interrupt\n");
    io_bit_count--;

    switch (one_wire_status)
    {
        case START:

            if (io_bit_count == 0)
            {
                io_bit_count = 16;
                one_wire_status = REQUEST;
            }

            break;
        case REQUEST:
            gpio_set_value(one_write_pin, io_data & (1U << 31));
            io_data <<= 1;

            if (io_bit_count == 0)
            {
                io_bit_count = 2;
                one_wire_status = WAITING;
            }

            break;
        case WAITING:

            if (io_bit_count == 0)
            {
                io_bit_count = 32;
                one_wire_status = RESPONSE;
            }

            if (io_bit_count == 1)
            {
                pinctrl_select_state(pctrl, pstate_in);
                gpio_set_value(one_write_pin, 1);
            }

            break;
        case RESPONSE:
            io_data = (io_data << 1) | gpio_get_value(one_write_pin);

            if (io_bit_count == 0)
            {
                io_bit_count = 2;
                one_wire_status = STOPING;
                gpio_set_value(one_write_pin, 1);
                pinctrl_select_state(pctrl, pstate_out);
                //one_wire_session_complete(one_wire_request, io_data);
            }

            break;
        case STOPING:

            if (io_bit_count == 0)
            {
                one_wire_status = IDLE;
                stop_timer_for_1wire();
            }

            break;
        default:
            stop_timer_for_1wire();
    }

    return IRQ_HANDLED;
}


static const unsigned char crc8_tab[] =
{
    0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
    0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D,
    0x70, 0x77, 0x7E, 0x79, 0x6C, 0x6B, 0x62, 0x65,
    0x48, 0x4F, 0x46, 0x41, 0x54, 0x53, 0x5A, 0x5D,
    0xE0, 0xE7, 0xEE, 0xE9, 0xFC, 0xFB, 0xF2, 0xF5,
    0xD8, 0xDF, 0xD6, 0xD1, 0xC4, 0xC3, 0xCA, 0xCD,
    0x90, 0x97, 0x9E, 0x99, 0x8C, 0x8B, 0x82, 0x85,
    0xA8, 0xAF, 0xA6, 0xA1, 0xB4, 0xB3, 0xBA, 0xBD,
    0xC7, 0xC0, 0xC9, 0xCE, 0xDB, 0xDC, 0xD5, 0xD2,
    0xFF, 0xF8, 0xF1, 0xF6, 0xE3, 0xE4, 0xED, 0xEA,
    0xB7, 0xB0, 0xB9, 0xBE, 0xAB, 0xAC, 0xA5, 0xA2,
    0x8F, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9D, 0x9A,
    0x27, 0x20, 0x29, 0x2E, 0x3B, 0x3C, 0x35, 0x32,
    0x1F, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0D, 0x0A,
    0x57, 0x50, 0x59, 0x5E, 0x4B, 0x4C, 0x45, 0x42,
    0x6F, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7D, 0x7A,
    0x89, 0x8E, 0x87, 0x80, 0x95, 0x92, 0x9B, 0x9C,
    0xB1, 0xB6, 0xBF, 0xB8, 0xAD, 0xAA, 0xA3, 0xA4,
    0xF9, 0xFE, 0xF7, 0xF0, 0xE5, 0xE2, 0xEB, 0xEC,
    0xC1, 0xC6, 0xCF, 0xC8, 0xDD, 0xDA, 0xD3, 0xD4,
    0x69, 0x6E, 0x67, 0x60, 0x75, 0x72, 0x7B, 0x7C,
    0x51, 0x56, 0x5F, 0x58, 0x4D, 0x4A, 0x43, 0x44,
    0x19, 0x1E, 0x17, 0x10, 0x05, 0x02, 0x0B, 0x0C,
    0x21, 0x26, 0x2F, 0x28, 0x3D, 0x3A, 0x33, 0x34,
    0x4E, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5C, 0x5B,
    0x76, 0x71, 0x78, 0x7F, 0x6A, 0x6D, 0x64, 0x63,
    0x3E, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2C, 0x2B,
    0x06, 0x01, 0x08, 0x0F, 0x1A, 0x1D, 0x14, 0x13,
    0xAE, 0xA9, 0xA0, 0xA7, 0xB2, 0xB5, 0xBC, 0xBB,
    0x96, 0x91, 0x98, 0x9F, 0x8A, 0x8D, 0x84, 0x83,
    0xDE, 0xD9, 0xD0, 0xD7, 0xC2, 0xC5, 0xCC, 0xCB,
    0xE6, 0xE1, 0xE8, 0xEF, 0xFA, 0xFD, 0xF4, 0xF3,
};

#define crc8_init(crc) ((crc) = 0XACU)
#define crc8(crc, v) ( (crc) = crc8_tab[(crc) ^(v)])

static void start_one_wire_session(unsigned char req)
{
    unsigned int tcon;
    printk("backlight_write\n");
    one_wire_status = START;
    gpio_set_value(one_write_pin, 1);
    pinctrl_select_state(pctrl, pstate_out);
    // IDLE to START
    {
        unsigned char crc;
        crc8_init(crc);
        crc8(crc, req);
        io_data = (req << 8) + crc;
        io_data <<= 16;
    }
    io_bit_count = 1;
    pinctrl_select_state(pctrl, pstate_out);
    timer->TCNTB3 = 650;
    //init tranfer and start timer
    tcon = timer->TCON;
    tcon &= ~(0xF << 16);
    tcon |= (1 << 17);
    timer->TCON = tcon;
    tcon |= (1 << 16);
    tcon |= (1 << 19);
    tcon &= ~(1 << 17);
    timer->TCON = tcon;
    timer->TINT_CSTAT |= 0x08;
    gpio_set_value(one_write_pin, 0);
}

static ssize_t backlight_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
{
    unsigned char reg, ret;
    ret = copy_from_user(&reg, buf, 1);

    if (ret < 0)
    {
        printk("%s copy_from_user error\n", __func__);
    }

    if (reg > 127)
        { reg = 127; }

    start_one_wire_session(reg + 0x80);
    return 1;
}


static int backlight_open(struct inode *inode, struct file *file)
{
    printk("backlight_open\n");
    return 0;
}

static int backlight_release(struct inode *inode, struct file *file)
{
    printk("backlight_exit\n");
    return 0;
}

static struct file_operations backlight_fops =
{
    .owner              = THIS_MODULE,
    .open               = backlight_open,
    .release            = backlight_release,
    .write              = backlight_write,
};
static struct device *dev;
static struct clk *base_clk;
static struct resource *res = NULL, *irq = NULL;
static int backlight_probe(struct platform_device *pdev)
{
    int ret;
    dev_t devid;
    dev = &pdev->dev;
    printk("enter %s\n", __func__);
    pctrl = devm_pinctrl_get(dev);

    if (pctrl == NULL)
    {
        printk("devm_pinctrl_get error\n");
        return -EINVAL;
    }

    pstate_in  = pinctrl_lookup_state(pctrl, "backlight_in");
    pstate_out = pinctrl_lookup_state(pctrl, "backlight_out");

    if (pstate_in == NULL || pstate_out == NULL)
    {
        printk("pinctrl_lookup_state error\n");
        return -EINVAL;
    }

    one_write_pin = of_get_named_gpio(dev->of_node, "tiny4412,backlight", 0);

    if (!one_write_pin)
    {
        printk("of_get_named_gpio error\n");
        return -EINVAL;
    }

    devm_gpio_request_one(dev, one_write_pin, GPIOF_OUT_INIT_HIGH, "one_write");
    //pinctrl_select_state(pctrl, pstate);
    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

    if (res == NULL)
    {
        printk("platform_get_resource error\n");
        return -EINVAL;
    }

    base_clk = devm_clk_get(&pdev->dev, "timers");

    if (IS_ERR(base_clk))
    {
        dev_err(dev, "failed to get timer base clk\n");
        return PTR_ERR(base_clk);
    }

    ret = clk_prepare_enable(base_clk);

    if (ret < 0)
    {
        dev_err(dev, "failed to enable base clock\n");
        return ret;
    }

    timer = devm_ioremap_resource(&pdev->dev, res);

    if (timer == NULL)
    {
        printk("devm_ioremap_resource error\n");
        return -EINVAL;
    }

    printk("timer: %x\n", (unsigned int)timer);
    timer->TCFG0  = 0xf00;
    timer->TCFG1  = 0x10004;
    irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);

    if (irq == NULL)
    {
        printk("platform_get_resource irq error\n");
        return -EINVAL;
    }

    ret = devm_request_irq(dev, irq->start, timer_for_1wire_interrupt , IRQF_TIMER, "backlight", NULL);

    if (ret)
    {
        dev_err(dev, "unable to request irq\n");
        return -EINVAL;
    }

    start_one_wire_session(0x60);

    if (alloc_chrdev_region(&devid, 0, 1, "backlight") < 0)
    {
        printk("%s ERROR\n", __func__);
        return -EINVAL;
    }

    major = MAJOR(devid);
    cdev_init(&backlight_cdev, &backlight_fops);
    cdev_add(&backlight_cdev, devid, 1);
    cls = class_create(THIS_MODULE, "backlight_demo");
    device_create(cls, NULL, MKDEV(major, 0), NULL, "backlight");
    return 0;
}

static int backlight_remove(struct platform_device *pdev)
{
    printk("enter %s\n", __func__);
    device_destroy(cls, MKDEV(major, 0));
    class_destroy(cls);
    cdev_del(&backlight_cdev);
    unregister_chrdev_region(MKDEV(major, 0), 1);
    devm_pinctrl_put(pctrl);
    devm_free_irq(dev, irq->start, NULL);
    clk_disable_unprepare(base_clk);
    devm_gpio_free(dev, one_write_pin);
    return 0;
}

static const struct of_device_id backlight_dt_ids[] =
{
    { .compatible = "tiny4412,backlight_demo", },
    {},
};

MODULE_DEVICE_TABLE(of, backlight_dt_ids);

static struct platform_driver backlight_driver =
{
    .driver        = {
        .name      = "backlight_demo",
        .of_match_table    = of_match_ptr(backlight_dt_ids),
    },
    .probe         = backlight_probe,
    .remove        = backlight_remove,
};

static int backlight_init(void)
{
    int ret;
    printk("enter %s\n", __func__);
    ret = platform_driver_register(&backlight_driver);

    if (ret)
    {
        printk(KERN_ERR "backlight demo: probe faid backlight: %d\n", ret);
    }

    return ret;
}

static void backlight_exit(void)
{
    printk("enter %s\n", __func__);
    platform_driver_unregister(&backlight_driver);
}

module_init(backlight_init);
module_exit(backlight_exit);
MODULE_LICENSE("GPL");

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