写多个寄存器

static int mpc_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, intnum)
{
    struct i2c_msg *pmsg;
    int i;
    int ret = 0;
    unsigned long orig_jiffies = jiffies;
    struct mpc_i2c *i2c = i2c_get_adapdata(adap);

mpc_i2c_start(i2c);    // 设置I2CCR[MEN], 使能I2C module

/* Allow bus up to 1s to become not busy */
    //一直读I2CSR[MBB]，等待I2C总线空闲下来
    while (readb(i2c->base + MPC_I2C_SR) & CSR_MBB) {
        if (signal_pending(current)) {
            pr_debug("I2C: Interrupted\n");
            writeccr(i2c, 0);
            return -EINTR;
        }
        if (time_after(jiffies, orig_jiffies + HZ)) {
            pr_debug("I2C: timeout\n");
            if (readb(i2c->base + MPC_I2C_SR) ==
                (CSR_MCF | CSR_MBB | CSR_RXAK))
                mpc_i2c_fixup(i2c);
            return -EIO;
        }
        schedule();
    }

for (i = 0; ret >= 0 && i < num; i++) {
        pmsg = &msgs[i];
        pr_debug("Doing %s %d bytes to 0x%02x - %d of %d messages\n",
             pmsg->flags & I2C_M_RD ? "read" : "write",
             pmsg->len, pmsg->addr, i + 1, num);        //根据消息里的flag进行读操作或写操作        if (pmsg->flags & I2C_M_RD) 
            ret = mpc_read(i2c, pmsg->addr, pmsg->buf, pmsg->len, i);
        else
            ret = mpc_write(i2c, pmsg->addr, pmsg->buf, pmsg->len, i);
    }
    mpc_i2c_stop(i2c);    //保证为I2CCSR[MSTA]为0，保证能触发STOP
    return (ret < 0) ? ret : num;
}

static int mpc_write(struct mpc_i2c *i2c, int target,
             const u8 * data, int length, int restart)
{
    int i;
    unsigned timeout = i2c->adap.timeout;
    u32 flags = restart ? CCR_RSTA : 0;

/* Start with MEN */    //以防万一，保证I2C模块使能起来
    if (!restart)
        writeccr(i2c, CCR_MEN);
    /* Start as master */       //写了I2CCR[CCR_MSTA]，触发CPU发起START信号
    writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_MTX | flags);
    /* Write target byte */     //CPU发送一个字节，slave I2C addr和0 (写操作bit) 
    writeb((target << 1), i2c->base + MPC_I2C_DR);

if (i2c_wait(i2c, timeout, 1) < 0)    //等待slave 发ACK
        return -1;

for (i = 0; i < length; i++) {
        /* Write data byte */
        writeb(data[i], i2c->base + MPC_I2C_DR); //CPU接着发数据，包括reg addr和data

if (i2c_wait(i2c, timeout, 1) < 0)       //等待slave 发ACK
            return -1;
    }

return 0;
}

static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing)
{
    unsigned long orig_jiffies = jiffies;
    u32 x;
    int result = 0;

if (i2c->irq == 0)
    {    //循环读I2CSR，直到I2CSR[MIF]置1
        while (!(readb(i2c->base + MPC_I2C_SR) & CSR_MIF)) {
            schedule();
            if (time_after(jiffies, orig_jiffies + timeout)) {
                pr_debug("I2C: timeout\n");
                writeccr(i2c, 0);
                result = -EIO;
                break;
            }
        }
        x = readb(i2c->base + MPC_I2C_SR);
        writeb(0, i2c->base + MPC_I2C_SR);
    } else {
        /* Interrupt mode */
        result = wait_event_interruptible_timeout(i2c->queue,
            (i2c->interrupt & CSR_MIF), timeout * HZ);

if (unlikely(result < 0)) {
            pr_debug("I2C: wait interrupted\n");
            writeccr(i2c, 0);
        } else if (unlikely(!(i2c->interrupt & CSR_MIF))) {
            pr_debug("I2C: wait timeout\n");
            writeccr(i2c, 0);
            result = -ETIMEDOUT;
        }

x = i2c->interrupt;
        i2c->interrupt = 0;
    }

if (result < 0)
        return result;

if (!(x & CSR_MCF)) {
        pr_debug("I2C: unfinished\n");
        return -EIO;
    }

if (x & CSR_MAL) {    //仲裁失败
        pr_debug("I2C: MAL\n");
        return -EIO;
    }

if (writing && (x & CSR_RXAK)) {//写后没收到ACK
        pr_debug("I2C: No RXAK\n");
        /* generate stop */
        writeccr(i2c, CCR_MEN);
        return -EIO;
    }
    return 0;
}

static int mpc_read(struct mpc_i2c *i2c, int target,
            u8 * data, int length, int restart)
{
    unsigned timeout = i2c->adap.timeout;
    int i;
    u32 flags = restart ? CCR_RSTA : 0;

/* Start with MEN */    //以防万一，保证I2C模块使能
    if (!restart)
        writeccr(i2c, CCR_MEN);
    /* Switch to read - restart */    //注意这里，再次把CCR_MSTA置1，再触发 START 
    writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_MTX | flags);

/* Write target address byte - this time with the read flag set */ 
    //CPU发送slave I2C addr和读操作1
    writeb((target << 1) | 1, i2c->base + MPC_I2C_DR);
      
     //等待Slave发ACK    if (i2c_wait(i2c, timeout, 1) < 0)
        return -1;

if (length) {
        if (length == 1)
            writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK);
        else //为什么不置 TXAK
            writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA);
        /* Dummy read */
        readb(i2c->base + MPC_I2C_DR);
    }

for (i = 0; i < length; i++) {
        if (i2c_wait(i2c, timeout, 0) < 0)
            return -1;

/* Generate txack on next to last byte */
        //注意这里TXAK置1，表示CPU每收到1byte数据后，会发送ACK
        if (i == length - 2) 
            writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MSTA | CCR_TXAK);

/* Generate stop on last byte */
        //注意这里CCR_MSTA [1->0] CPU会触发STOP
        if (i == length - 1)    
            writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_TXAK);

data[i] = readb(i2c->base + MPC_I2C_DR);
    }

return length;
}