I.MX6 PWM buzzer driver hacking with Demo test

/*****************************************************************************
 *             I.MX6 PWM buzzer driver hacking with Demo test
 * 声明：
 *     1. I.MX6和OK335xS实现PWM驱动函数是不一样的；
 *     2. 通过分析PWM驱动，了解有哪些驱动函数可以用；
 *     3. 使用I.MX6提供的PWM函数，编写测试用例buzzer驱动；
 *     4. 使用C编写测试程序。
 *
 *                                     2015-10-20 晴 深圳 南山平山村 曾剑锋
 ****************************************************************************/

                \\\\\\\\\\\\\-*- 目录 -*-/////////////
                |  一、cat arch/arm/plat-mxc/pwm.c
                |  二、cat driver/misc/pwm_buzzer.c
                |  三、cat main.c (demo test)
                --------------------------------------

一、cat arch/arm/plat-mxc/pwm.c
    /*
     * simple driver for PWM (Pulse Width Modulator) controller
     *
     * This program is free software; you can redistribute it and/or modify
     * it under the terms of the GNU General Public License version 2 as
     * published by the Free Software Foundation.
     *
     * Derived from pxa PWM driver by eric miao <eric.miao@marvell.com>
     * Copyright 2009-2013 Freescale Semiconductor, Inc. All Rights Reserved.
     */

    #include <linux/module.h>
    #include <linux/kernel.h>
    #include <linux/platform_device.h>
    #include <linux/slab.h>
    #include <linux/err.h>
    #include <linux/clk.h>
    #include <linux/io.h>
    #include <linux/pwm.h>
    #include <linux/fsl_devices.h>
    #include <mach/hardware.h>

    /* i.MX1 and i.MX21 share the same PWM function block: */

    #define MX1_PWMC    0x00   /* PWM Control Register */
    #define MX1_PWMS    0x04   /* PWM Sample Register */
    #define MX1_PWMP    0x08   /* PWM Period Register */

    /* i.MX27, i.MX31, i.MX35 share the same PWM function block: */

    #define MX3_PWMCR                 0x00    /* PWM Control Register */
    #define MX3_PWMSAR                0x0C    /* PWM Sample Register */
    #define MX3_PWMPR                 0x10    /* PWM Period Register */
    #define MX3_PWMCR_PRESCALER(x)      (((x - 1) & 0xFFF) << 4)
    #define MX3_PWMCR_DOZEEN            (1 << 24)
    #define MX3_PWMCR_WAITEN            (1 << 23)
    #define MX3_PWMCR_DBGEN                (1 << 22)
    #define MX3_PWMCR_CLKSRC_IPG_HIGH   (2 << 16)
    #define MX3_PWMCR_CLKSRC_IPG        (1 << 16)
    #define MX3_PWMCR_SWR               (1 << 3)
    #define MX3_PWMCR_EN                (1 << 0)

    #define MX3_PWMCR_STOPEN            (1 << 25)
    #define MX3_PWMCR_DOZEEN            (1 << 24)
    #define MX3_PWMCR_WAITEN            (1 << 23)
    #define MX3_PWMCR_DBGEN                (1 << 22)
    #define MX3_PWMCR_CLKSRC_IPG        (1 << 16)
    #define MX3_PWMCR_CLKSRC_IPG_32k    (3 << 16)

    struct pwm_device {
        struct list_head    node;
        struct platform_device *pdev;

        const char    *label;
        struct clk    *clk;

        int        clk_enabled;
        void __iomem    *mmio_base;

        unsigned int    use_count;
        unsigned int    pwm_id;
        int        pwmo_invert;
        void (*enable_pwm_pad)(void);
        void (*disable_pwm_pad)(void);
    };

    /**
     * 1. 操作PWM用到duty(duty_ns)、period(period_ns)2个参数；
     * 2. period就是频率参数（周期时间），duty为占空比；
     * 3. period和duty的参数单位为纳秒（ns）；
     * 4. 1s=1000ms=1000000us=1000000000ns；
     * 5. period最大的取值范围为0—1000000000，而duty则取值0—period值之间；
     * 6. 平时我们可能更喜欢使用频率（Hz）来表示period，占空比来表示duty；
     */
    int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
    {
        if (pwm == NULL || period_ns == 0 || duty_ns > period_ns)
            return -EINVAL;

        if (!(cpu_is_mx1() || cpu_is_mx21())) {
            unsigned long long c;
            unsigned long period_cycles, duty_cycles, prescale;
            u32 cr;

            if (pwm->pwmo_invert)
                duty_ns = period_ns - duty_ns;

            c = clk_get_rate(pwm->clk);
            c = c * period_ns;
            do_div(c, 1000000000);
            period_cycles = c;

            prescale = period_cycles / 0x10000 + 1;

            period_cycles /= prescale;
            c = (unsigned long long)period_cycles * duty_ns;
            do_div(c, period_ns);
            duty_cycles = c;

            /*
             * according to imx pwm RM, the real period value should be
             * PERIOD value in PWMPR plus 2.
             */
            if (period_cycles > 2)
                period_cycles -= 2;
            else
                period_cycles = 0;

            writel(duty_cycles, pwm->mmio_base + MX3_PWMSAR);
            writel(period_cycles, pwm->mmio_base + MX3_PWMPR);

            cr = MX3_PWMCR_PRESCALER(prescale) |
                MX3_PWMCR_STOPEN | MX3_PWMCR_DOZEEN |
                MX3_PWMCR_WAITEN | MX3_PWMCR_DBGEN;

            if (cpu_is_mx25())
                cr |= MX3_PWMCR_CLKSRC_IPG;
            else
                cr |= MX3_PWMCR_CLKSRC_IPG_HIGH;

            writel(cr, pwm->mmio_base + MX3_PWMCR);
        } else if (cpu_is_mx1() || cpu_is_mx21()) {
            /* The PWM subsystem allows for exact frequencies. However,
             * I cannot connect a scope on my device to the PWM line and
             * thus cannot provide the program the PWM controller
             * exactly. Instead, I'm relying on the fact that the
             * Bootloader (u-boot or WinCE+haret) has programmed the PWM
             * function group already. So I'll just modify the PWM sample
             * register to follow the ratio of duty_ns vs. period_ns
             * accordingly.
             *
             * This is good enough for programming the brightness of
             * the LCD backlight.
             *
             * The real implementation would divide PERCLK[0] first by
             * both the prescaler (/1 .. /128) and then by CLKSEL
             * (/2 .. /16).
             */
            u32 max = readl(pwm->mmio_base + MX1_PWMP);
            u32 p;
            if (pwm->pwmo_invert)
                duty_ns = period_ns - duty_ns;
            p = max * duty_ns / period_ns;
            writel(max - p, pwm->mmio_base + MX1_PWMS);
        } else {
            BUG();
        }

        return 0;
    }
    EXPORT_SYMBOL(pwm_config);

    /**
     * 使能pwm
     */
    int pwm_enable(struct pwm_device *pwm)
    {
        unsigned long reg;
        int rc = 0;

        if (!pwm->clk_enabled) {
            rc = clk_enable(pwm->clk);
            if (!rc)
                pwm->clk_enabled = 1;
        }

        reg = readl(pwm->mmio_base + MX3_PWMCR);
        reg |= MX3_PWMCR_EN;
        writel(reg, pwm->mmio_base + MX3_PWMCR);

        if (pwm->enable_pwm_pad)
            pwm->enable_pwm_pad();

        return rc;
    }
    EXPORT_SYMBOL(pwm_enable);

    /**
     * 关闭pwm
     */
    void pwm_disable(struct pwm_device *pwm)
    {
        if (pwm->disable_pwm_pad)
            pwm->disable_pwm_pad();

        writel(MX3_PWMCR_SWR, pwm->mmio_base + MX3_PWMCR);
        while (readl(pwm->mmio_base + MX3_PWMCR) & MX3_PWMCR_SWR)
            ;

        if (pwm->clk_enabled) {
            clk_disable(pwm->clk);
            pwm->clk_enabled = 0;
        }
    }
    EXPORT_SYMBOL(pwm_disable);

    static DEFINE_MUTEX(pwm_lock);
    static LIST_HEAD(pwm_list);

    /**
     * 通过pwm的id来表示申请pwm通道，label只是表示其名字，名字可以随意取
     */
    struct pwm_device *pwm_request(int pwm_id, const char *label)
    {
        struct pwm_device *pwm;
        int found = 0;

        mutex_lock(&pwm_lock);

        list_for_each_entry(pwm, &pwm_list, node) {
            if (pwm->pwm_id == pwm_id) {
                found = 1;
                break;
            }
        }

        if (found) {
            if (pwm->use_count == 0) {
                pwm->use_count++;
                pwm->label = label;
            } else
                pwm = ERR_PTR(-EBUSY);
        } else
            pwm = ERR_PTR(-ENOENT);

        mutex_unlock(&pwm_lock);
        return pwm;
    }
    EXPORT_SYMBOL(pwm_request);

    /**
     * 前面申请了pwm，通过这个函数来释放pwm
     */
    void pwm_free(struct pwm_device *pwm)
    {
        mutex_lock(&pwm_lock);

        if (pwm->use_count) {
            pwm->use_count--;
            pwm->label = NULL;
        } else
            pr_warning("PWM device already freed\n");

        mutex_unlock(&pwm_lock);
    }
    EXPORT_SYMBOL(pwm_free);

    /**
     * 这里是pwm控制器注册函数
     */
    static int __devinit mxc_pwm_probe(struct platform_device *pdev)
    {
        struct pwm_device *pwm;
        struct resource *r;
        struct mxc_pwm_platform_data *plat_data = pdev->dev.platform_data;
        int ret = 0;

        pwm = kzalloc(sizeof(struct pwm_device), GFP_KERNEL);
        if (pwm == NULL) {
            dev_err(&pdev->dev, "failed to allocate memory\n");
            return -ENOMEM;
        }

        pwm->clk = clk_get(&pdev->dev, "pwm");

        if (IS_ERR(pwm->clk)) {
            ret = PTR_ERR(pwm->clk);
            goto err_free;
        }

        pwm->clk_enabled = 0;

        pwm->use_count = 0;
        pwm->pwm_id = pdev->id;
        pwm->pdev = pdev;
        if (plat_data != NULL) {
            pwm->pwmo_invert = plat_data->pwmo_invert;
            pwm->enable_pwm_pad = plat_data->enable_pwm_pad;
            pwm->disable_pwm_pad = plat_data->disable_pwm_pad;
        }

        r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (r == NULL) {
            dev_err(&pdev->dev, "no memory resource defined\n");
            ret = -ENODEV;
            goto err_free_clk;
        }

        r = request_mem_region(r->start, r->end - r->start + 1, pdev->name);
        if (r == NULL) {
            dev_err(&pdev->dev, "failed to request memory resource\n");
            ret = -EBUSY;
            goto err_free_clk;
        }

        pwm->mmio_base = ioremap(r->start, r->end - r->start + 1);
        if (pwm->mmio_base == NULL) {
            dev_err(&pdev->dev, "failed to ioremap() registers\n");
            ret = -ENODEV;
            goto err_free_mem;
        }

        mutex_lock(&pwm_lock);
        list_add_tail(&pwm->node, &pwm_list);
        mutex_unlock(&pwm_lock);

        platform_set_drvdata(pdev, pwm);
        return 0;

    err_free_mem:
        release_mem_region(r->start, r->end - r->start + 1);
    err_free_clk:
        clk_put(pwm->clk);
    err_free:
        kfree(pwm);
        return ret;
    }

    static int __devexit mxc_pwm_remove(struct platform_device *pdev)
    {
        struct pwm_device *pwm;
        struct resource *r;

        pwm = platform_get_drvdata(pdev);
        if (pwm == NULL)
            return -ENODEV;

        mutex_lock(&pwm_lock);
        list_del(&pwm->node);
        mutex_unlock(&pwm_lock);

        iounmap(pwm->mmio_base);

        r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        release_mem_region(r->start, r->end - r->start + 1);

        clk_put(pwm->clk);

        kfree(pwm);
        return 0;
    }

    static struct platform_driver mxc_pwm_driver = {
        .driver        = {
            .name    = "mxc_pwm",
        },
        .probe        = mxc_pwm_probe,
        .remove        = __devexit_p(mxc_pwm_remove),
    };

    static int __init mxc_pwm_init(void)
    {
        return platform_driver_register(&mxc_pwm_driver);
    }
    arch_initcall(mxc_pwm_init);

    static void __exit mxc_pwm_exit(void)
    {
        platform_driver_unregister(&mxc_pwm_driver);
    }
    module_exit(mxc_pwm_exit);

    MODULE_LICENSE("GPL v2");
    MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");

二、cat driver/misc/pwm_buzzer.c
    #include <linux/init.h>
    #include <linux/module.h>
    #include <linux/moduleparam.h>
    #include <linux/errno.h>
    #include <linux/miscdevice.h>
    #include <linux/types.h>
    #include <linux/io.h>
    #include <linux/pwm.h>
    #include <linux/fs.h>  

    #define BUZZER_FREQENCY 1
    #define DEV_NAME    "buzzer"

    /*pwm for this buzzer*/
    struct pwm_device *pwm = NULL;

    static int buzzer_open(struct inode *inode, struct file *filp)
    {

        if(pwm != NULL)
            return -EBUSY;

        /**
         * buzzer正好挂载在I.MX6的pwm4上，所以这里申请3号（从零开始算）PWM
         */
        pwm = pwm_request(3, "buzzer");
        if ( pwm == NULL ) {
            printk("buzzer open error.\n");
        }

        return 0;
    }

    static int buzzer_release(struct inode *inode, struct file *filp)
    {
        pwm_disable(pwm);               // 关闭pwm
        pwm_free(pwm);                  // 释放pwm
        pwm = NULL;

        return 0;
    }

    static long buzzer_ioctl(struct file *filp,
                            unsigned int cmd, unsigned long arg)
    {
        if(pwm == NULL)
            return -EINVAL;

        if(arg > 20000 || arg < 0)
            return -EINVAL;

        switch (cmd) {
        case BUZZER_FREQENCY:
            if(arg==0)
                pwm_disable(pwm);
            else
            {
                pwm_config(pwm, 1000000000/arg/2, 1000000000/arg);
                pwm_enable(pwm);
            }
            break;
        default:
            break;
        }

        return 0;
    }

    static struct file_operations buzzer_fops = {
        .owner              = THIS_MODULE,
        .unlocked_ioctl     = buzzer_ioctl,
        .open               = buzzer_open,
        .release            = buzzer_release,
    };

    static struct miscdevice buzzer_miscdev =
    {
         .minor  = MISC_DYNAMIC_MINOR,
         .name   = DEV_NAME,
         .fops   = &buzzer_fops,
    };

    static int __init buzzer_init(void)
    {
        printk(" zengjf check buzzer init.\n");
        misc_register(&buzzer_miscdev);
        return 0;
    }

    static void __exit buzzer_exit(void)
    {
       misc_deregister(&buzzer_miscdev);
    }

    module_init(buzzer_init);
    module_exit(buzzer_exit);

    MODULE_DESCRIPTION("pwm_buzzer driver");
    MODULE_LICENSE("GPL");

三、cat main.c (demo test)
    ......
    #define PWM_IOCTL_SET_FREQ  1
    #define PWM_IOCTL_STOP      0
    ......
    int fd = open("dev/buzzer", O_RDWR);
    ......
    // 传入频率2000Hz
    ioctl(fd, PWM_IOCTL_SET_FREQ, 2000);
    ......
    ioctl(fd, PWM_IOCTL_STOP);
    ......
    close(fd);