MediaTech(MTK) MT7628 MT7688 OpenWRT 下 PWM驱动简要分析

前言：

    由于网络上关于mt7628和mt7688 pwm相关的资料非常少，所以只能自己慢慢琢磨。虽然研究的心得没有多少，但是其实也是费了不少精力，希望转载文章时，保留出处。佐须之男，专业从事网络设备(路由器)等嵌入式开发和技术咨询工作。

#include <linux/err.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/slab.h>
#include <linux/types.h>
#define NUM_PWM        4
/*  mt7628/mt7688 共有4路原生PWM分别是PWM0，PWM1，PWM3，PWM3。
    其中PWM2和PWM3和UART1复用，在使用PWM2和PWM3时需要关闭复用。
*/

/* PWM registers and bits definitions */
#define PWMCON            0x00    /* PWM Conntrol 寄存器 */
#define PWMHDUR            0x04    /* PWM High Duration 寄存器 */
#define PWMLDUR            0x08    /* PWM Low Duration 寄存器 */ 
#define PWMGDUR            0x0c    /* PWM Guard Duration 寄存器 */
#define PWMWAVENUM        0x28     /* PWM Wave Num 寄存器 */
#define PWMDWIDTH        0x2c    /* PWM Data Width 寄存器 */
#define PWMTHRES        0x30    /* PWM Thresh 寄存器 */
/**
 * struct mtk_pwm_chip - struct representing pwm chip
 *
 * @mmio_base: base address of pwm chip
 * @chip: linux pwm chip representation
 */
struct mtk_pwm_chip {
    void __iomem *mmio_base;
    struct pwm_chip chip;
};
static inline struct mtk_pwm_chip *to_mtk_pwm_chip(struct pwm_chip *chip)
{
    return container_of(chip, struct mtk_pwm_chip, chip);
}
static inline u32 mtk_pwm_readl(struct mtk_pwm_chip *chip, unsigned int num,
                  unsigned long offset)
{
    return ioread32(chip->mmio_base + 0x10 + (num * 0x40) + offset);
}
static inline void mtk_pwm_writel(struct mtk_pwm_chip *chip,
                    unsigned int num, unsigned long offset,
                    unsigned long val)
{
    iowrite32(val, chip->mmio_base + 0x10 + (num * 0x40) + offset);
}
static int mtk_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
                int duty_ns, int period_ns)
{
    struct mtk_pwm_chip *pc = to_mtk_pwm_chip(chip);
    u32 resolution = 100 / 4;
     /* 由于PWM是由40MHZ基准频率分频所得，所以PWM的频率是25ns的倍数关系 perdios_ns = 25*2^clkdiv 0 <= clkdiv <=7 */
    u32 clkdiv = 0; 
    /* 分频倍数分别是 0 1 2 4 8 16 32 64 128 , 所以 0 <= clkdiv <=7  */
    while (period_ns / resolution  > 8191) {
        clkdiv++;
        resolution *= 2;
    }
    if (clkdiv > 7)
        return -1;
    mtk_pwm_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | BIT(3) | clkdiv);     
    /* 设置控制寄存器，设置基准频率是40MHZ和分频倍数 */
    mtk_pwm_writel(pc, pwm->hwpwm, PWMDWIDTH, period_ns / resolution);    
    /* 设置总周期，T */
    mtk_pwm_writel(pc, pwm->hwpwm, PWMTHRES, duty_ns / resolution);     
    /* 设置上升沿周期t，占空比 = t/T*100  */
    return 0;
}
static int mtk_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
{
    struct mtk_pwm_chip *pc = to_mtk_pwm_chip(chip);
    u32 val;
    val = ioread32(pc->mmio_base);
    val |= BIT(pwm->hwpwm);
    iowrite32(val, pc->mmio_base);
    return 0;
}
static void mtk_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
{
    struct mtk_pwm_chip *pc = to_mtk_pwm_chip(chip);
    u32 val;
    val = ioread32(pc->mmio_base);
    val &= ~BIT(pwm->hwpwm);
    iowrite32(val, pc->mmio_base);
}
static const struct pwm_ops mtk_pwm_ops = {
    .config = mtk_pwm_config,
    .enable = mtk_pwm_enable,
    .disable = mtk_pwm_disable,
    .owner = THIS_MODULE,
};
static int mtk_pwm_probe(struct platform_device *pdev)
{
    struct mtk_pwm_chip *pc;
    struct resource *r;
    int ret;
    pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
    if (!pc)
        return -ENOMEM;
    r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    pc->mmio_base = devm_ioremap_resource(&pdev->dev, r);
    if (IS_ERR(pc->mmio_base))
        return PTR_ERR(pc->mmio_base);
    platform_set_drvdata(pdev, pc);
    pc->chip.dev = &pdev->dev;
    pc->chip.ops = &mtk_pwm_ops;
    pc->chip.base = -1;
    pc->chip.npwm = NUM_PWM;
    ret = pwmchip_add(&pc->chip);
    if (ret < 0)
        dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
    return ret;
}
static int mtk_pwm_remove(struct platform_device *pdev)
{
    struct mtk_pwm_chip *pc = platform_get_drvdata(pdev);
    int i;
    for (i = 0; i < NUM_PWM; i++)
        pwm_disable(&pc->chip.pwms[i]);
    return pwmchip_remove(&pc->chip);
}
static const struct of_device_id mtk_pwm_of_match[] = {
    { .compatible = "mediatek,mt7628-pwm" },
    { }
};
MODULE_DEVICE_TABLE(of, mtk_pwm_of_match);
static struct platform_driver mtk_pwm_driver = {
    .driver = {
        .name = "mtk-pwm",
        .owner = THIS_MODULE,
        .of_match_table = mtk_pwm_of_match,
    },
    .probe = mtk_pwm_probe,
    .remove = mtk_pwm_remove,
};
module_platform_driver(mtk_pwm_driver);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("John Crispin <blogic@openwrt.org>");
MODULE_ALIAS("platform:mtk-pwm");