static int copy_sleep_history(struct sleep_history *buf, int count)
{
	int c, err;
	int head, tail;
	struct sleep_history *ring_buf;

	if (!buf) {
		err = -EINVAL;
		goto err_invalid;
	}
	memset(buf, 0, count * sizeof(struct sleep_history));

	ring_buf = (struct sleep_history *)(sleep_history_data.sleep_history.buf);
	head = sleep_history_data.sleep_history.head;
	tail = sleep_history_data.sleep_history.tail;

	c = CIRC_CNT(head, tail, SLEEP_HISTORY_RINGBUFFER_SIZE);
	if (c == 0) {
		err = -EINVAL;
		goto err_read;
	} else  if (c == SLEEP_HISTORY_RINGBUFFER_SIZE - 1) {
		c = CIRC_CNT_TO_END(head, tail, SLEEP_HISTORY_RINGBUFFER_SIZE);
		memcpy(buf, ring_buf + tail, c * sizeof(struct sleep_history));
		memcpy(buf + c, ring_buf,
			(SLEEP_HISTORY_RINGBUFFER_SIZE-c) * sizeof(struct sleep_history));
		c = SLEEP_HISTORY_RINGBUFFER_SIZE - 1;
	} else
		memcpy(buf, ring_buf + tail, c * sizeof(struct sleep_history));

	return c;

err_invalid:
err_read:
	return err;
}

/* Called with u->lock taken */
static void tegra_start_next_tx(struct tegra_uart_port *t)
{
	unsigned long tail;
	unsigned long count;

	struct circ_buf *xmit;

	xmit = &t->uport.state->xmit;
	tail = (unsigned long)&xmit->buf[xmit->tail];
	count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);


	dev_vdbg(t->uport.dev, "+%s %lu %d\n", __func__, count,
		t->tx_in_progress);

	if (count == 0)
		goto out;

	if (!t->use_tx_dma || count < TEGRA_UART_MIN_DMA)
		tegra_start_pio_tx(t, count);
	else if (BYTES_TO_ALIGN(tail) > 0)
		tegra_start_pio_tx(t, BYTES_TO_ALIGN(tail));
	else
		tegra_start_dma_tx(t, count);

out:
	dev_vdbg(t->uport.dev, "-%s", __func__);
}

static void uart_task_action(unsigned long data)
{
	struct uart_pxa_port *up = (struct uart_pxa_port *)data;
	struct circ_buf *xmit = &up->port.state->xmit;
	unsigned char *tmp = up->uart_dma.txdma_addr;
	unsigned long flags;
	int count = 0, c;

	/* if the tx is stop, just return.*/
	if (up->uart_dma.tx_stop)
		return;

	spin_lock_irqsave(&up->port.lock, flags);
	if (up->uart_dma.dma_status & TX_DMA_RUNNING) {
		spin_unlock_irqrestore(&up->port.lock, flags);
		return;
	}

	up->uart_dma.dma_status |= TX_DMA_RUNNING;
	while (1) {
		c = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
		if (c <= 0)
			break;

		memcpy(tmp, xmit->buf + xmit->tail, c);
		xmit->tail = (xmit->tail + c) & (UART_XMIT_SIZE - 1);
		tmp += c;
		count += c;
		up->port.icount.tx += c;
	}
	spin_unlock_irqrestore(&up->port.lock, flags);

	pr_debug("count =%d", count);
	pxa_uart_transmit_dma_start(up, count);
}

static int stmp_appuart_copy_tx(struct uart_port *u, u8 *target,
		int tx_buffer_size)
{
	int last = 0, portion;
	struct circ_buf *xmit = &u->info->xmit;

	while (last < tx_buffer_size) {	/* let's fill the only descriptor */
		if (u->x_char) {
			target[last++] = u->x_char;
			u->x_char = 0;
		} else if (!uart_circ_empty(xmit) && !uart_tx_stopped(u)) {
			portion = min((u32)tx_buffer_size,
				(u32)uart_circ_chars_pending(xmit));
			portion = min((u32)portion,
				(u32)CIRC_CNT_TO_END(xmit->head, xmit->tail,
					UART_XMIT_SIZE));
			memcpy(target + last, &xmit->buf[xmit->tail], portion);
			xmit->tail = (xmit->tail + portion) &
				(UART_XMIT_SIZE - 1);
			if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
				uart_write_wakeup(u);
			last += portion;
		} else { /* All tx data copied into buffer */
			return last;
		}
	}
	return last;
}

static int spi_read(struct bathos_pipe *pipe, char *buf, int len)
{
	struct spi_data *data = &spi_data;
	int flags;
	int l;

	interrupt_disable(flags);
	l = min(len, CIRC_CNT_TO_END(data->cbufrx.head, data->cbufrx.tail,
				     SPI_BUF_SIZE));

	if (!l) {
		interrupt_restore(flags);
		return -EAGAIN;
	}

	memcpy(buf, &data->bufrx[data->cbufrx.tail], l);
	data->cbufrx.tail = (data->cbufrx.tail + l) & (SPI_BUF_SIZE - 1);
	data->overrun = 0;

	if (CIRC_CNT(data->cbufrx.head, data->cbufrx.tail, SPI_BUF_SIZE))
		pipe_dev_trigger_event(&__spi_dev, &evt_pipe_input_ready,
				       EVT_PRIO_MAX);

	interrupt_restore(flags);
	return l;
}

/********************************************************************************
 *  Description:
 *   Input Args:
 *  Output Args:
 * Return Value:
 ********************************************************************************/
int main (int argc, char **argv)
{
    int i, len;
    struct circ_buf        tx_ring; 
    char   data[LEN];
    char   buf[LEN];

    memset(&tx_ring, 0, sizeof(struct circ_buf)); 
    tx_ring.buf = malloc(CIRC_BUF_SIZE); 
    if( NULL == tx_ring.buf )
    {
        printf("Allocate Ring buffer failure.\n");
        return -1;
    }

    memset(data, 0, sizeof(data));
    /* Prepare for the data */
    for(i=0; i<sizeof(data); i++)
    {
        data[i] = 30+i;
    }

    printf("CIRC_SPACE: %d\n", CIRC_SPACE(tx_ring.head, tx_ring.tail, CIRC_BUF_SIZE));
    printf("CIRC_SPACE_TO_END: %d\n", CIRC_SPACE_TO_END(tx_ring.head, tx_ring.tail, CIRC_BUF_SIZE));
    printf("CIRC_CNT: %d\n", CIRC_CNT(tx_ring.head, tx_ring.tail, CIRC_BUF_SIZE));
    printf("CIRC_CNT_TO_END: %d\n", CIRC_CNT_TO_END(tx_ring.head, tx_ring.tail, CIRC_BUF_SIZE));
    while(1)
    {
       produce_item(&tx_ring, data, sizeof(data));
       len = consume_item(&tx_ring, buf, sizeof(buf) );
       sleep(1);
    }

    return 0;
} /* ----- End of main() ----- */

static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
				size_t count, loff_t *ppos)
{
	struct userio_device *userio = file->private_data;
	int error;
	size_t nonwrap_len, copylen;
	unsigned char buf[USERIO_BUFSIZE];
	unsigned long flags;

	/*
	 * By the time we get here, the data that was waiting might have
	 * been taken by another thread. Grab the buffer lock and check if
	 * there's still any data waiting, otherwise repeat this process
	 * until we have data (unless the file descriptor is non-blocking
	 * of course).
	 */
	for (;;) {
		spin_lock_irqsave(&userio->buf_lock, flags);

		nonwrap_len = CIRC_CNT_TO_END(userio->head,
					      userio->tail,
					      USERIO_BUFSIZE);
		copylen = min(nonwrap_len, count);
		if (copylen) {
			memcpy(buf, &userio->buf[userio->tail], copylen);
			userio->tail = (userio->tail + copylen) %
							USERIO_BUFSIZE;
		}

		spin_unlock_irqrestore(&userio->buf_lock, flags);

		if (nonwrap_len)
			break;

		/* buffer was/is empty */
		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;

		/*
		 * count == 0 is special - no IO is done but we check
		 * for error conditions (see above).
		 */
		if (count == 0)
			return 0;

		error = wait_event_interruptible(userio->waitq,
						 userio->head != userio->tail);
		if (error)
			return error;
	}

	if (copylen)
		if (copy_to_user(user_buffer, buf, copylen))
			return -EFAULT;

	return copylen;
}

size_t whitebox_user_source_data_available(struct whitebox_user_source *user_source,
        unsigned long *src)
{
    long head, tail, data;
    head = ACCESS_ONCE(user_source->buf.head);
    tail = user_source->buf.tail;
    data = CIRC_CNT_TO_END(head, tail, user_source->buf_size);
    d_printk(7, "%ld\n", data);
    *src = (long)user_source->buf.buf + tail;
    return data;
}

int serial8250_tx_dma(struct uart_8250_port *p)
{
	struct uart_8250_dma		*dma = p->dma;
	struct circ_buf			*xmit = &p->port.state->xmit;
	struct dma_async_tx_descriptor	*desc;
	int ret;

	if (dma->tx_running)
		return 0;

	if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) {
		/* We have been called from __dma_tx_complete() */
		serial8250_rpm_put_tx(p);
		return 0;
	}

	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);

	desc = dmaengine_prep_slave_single(dma->txchan,
					   dma->tx_addr + xmit->tail,
					   dma->tx_size, DMA_MEM_TO_DEV,
					   DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
	if (!desc) {
		ret = -EBUSY;
		goto err;
	}

	dma->tx_running = 1;
	desc->callback = __dma_tx_complete;
	desc->callback_param = p;

	dma->tx_cookie = dmaengine_submit(desc);

	dma_sync_single_for_device(dma->txchan->device->dev, dma->tx_addr,
				   UART_XMIT_SIZE, DMA_TO_DEVICE);

	dma_async_issue_pending(dma->txchan);
	if (dma->tx_err) {
		dma->tx_err = 0;
		if (p->ier & UART_IER_THRI) {
			p->ier &= ~UART_IER_THRI;
			serial_out(p, UART_IER, p->ier);
		}
	}
	return 0;
err:
	dma->tx_err = 1;
	return ret;
}

static int sprd_tx_buf_remap(struct uart_port *port)
{
	struct sprd_uart_port *sp =
		container_of(port, struct sprd_uart_port, port);
	struct circ_buf *xmit = &port->state->xmit;

	sp->tx_dma.trans_len =
		CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);

	sp->tx_dma.phys_addr = dma_map_single(port->dev,
					      (void *)&(xmit->buf[xmit->tail]),
					      sp->tx_dma.trans_len,
					      DMA_TO_DEVICE);
	return dma_mapping_error(port->dev, sp->tx_dma.phys_addr);
}

static void transmit_chars_write(struct uart_port *port, struct circ_buf *xmit)
{
	while (!uart_circ_empty(xmit)) {
		unsigned long ra = __pa(xmit->buf + xmit->tail);
		unsigned long len, status, sent;

		len = CIRC_CNT_TO_END(xmit->head, xmit->tail,
				      UART_XMIT_SIZE);
		status = sun4v_con_write(ra, len, &sent);
		if (status != HV_EOK)
			break;
		xmit->tail = (xmit->tail + sent) & (UART_XMIT_SIZE - 1);
		port->icount.tx += sent;
	}
}

static void tegra_tcu_uart_start_tx(struct uart_port *port)
{
	struct tegra_tcu *tcu = port->private_data;
	struct circ_buf *xmit = &port->state->xmit;
	unsigned long count;

	for (;;) {
		count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
		if (!count)
			break;

		tegra_tcu_write(tcu, &xmit->buf[xmit->tail], count);
		xmit->tail = (xmit->tail + count) & (UART_XMIT_SIZE - 1);
	}

	uart_write_wakeup(port);
}

/*
 * serial_buf_get
 *
 * Get data from the circular buffer and copy to the given buffer.
 * Restrict to the amount of data available.
 *
 * Return the number of bytes copied.
 */
static int serial_buf_get(struct circ_buf *cb, char *buf, int count)
{
	int c, ret = 0;
	while (1) {
		c = CIRC_CNT_TO_END(cb->head, cb->tail, AIRCABLE_BUF_SIZE);
		if (count < c)
			c = count;
		if (c <= 0)
			break;
		memcpy(buf, cb->buf + cb->tail, c);
		cb->tail = (cb->tail + c) & (AIRCABLE_BUF_SIZE-1);
		buf += c;
		count -= c;
		ret= c;
	}
	return ret;
}

static ssize_t arcmsr_sysfs_iop_message_read(struct file *filp,
					     struct kobject *kobj,
					     struct bin_attribute *bin,
					     char *buf, loff_t off,
					     size_t count)
{
	struct device *dev = container_of(kobj,struct device,kobj);
	struct Scsi_Host *host = class_to_shost(dev);
	struct AdapterControlBlock *acb = (struct AdapterControlBlock *) host->hostdata;
	uint8_t *ptmpQbuffer;
	int32_t allxfer_len = 0;
	unsigned long flags;

	if (!capable(CAP_SYS_ADMIN))
		return -EACCES;

	/* do message unit read. */
	ptmpQbuffer = (uint8_t *)buf;
	spin_lock_irqsave(&acb->rqbuffer_lock, flags);
	if (acb->rqbuf_getIndex != acb->rqbuf_putIndex) {
		unsigned int tail = acb->rqbuf_getIndex;
		unsigned int head = acb->rqbuf_putIndex;
		unsigned int cnt_to_end = CIRC_CNT_TO_END(head, tail, ARCMSR_MAX_QBUFFER);

		allxfer_len = CIRC_CNT(head, tail, ARCMSR_MAX_QBUFFER);
		if (allxfer_len > ARCMSR_API_DATA_BUFLEN)
			allxfer_len = ARCMSR_API_DATA_BUFLEN;

		if (allxfer_len <= cnt_to_end)
			memcpy(ptmpQbuffer, acb->rqbuffer + tail, allxfer_len);
		else {
			memcpy(ptmpQbuffer, acb->rqbuffer + tail, cnt_to_end);
			memcpy(ptmpQbuffer + cnt_to_end, acb->rqbuffer, allxfer_len - cnt_to_end);
		}
		acb->rqbuf_getIndex = (acb->rqbuf_getIndex + allxfer_len) % ARCMSR_MAX_QBUFFER;
	}
	if (acb->acb_flags & ACB_F_IOPDATA_OVERFLOW) {
		struct QBUFFER __iomem *prbuffer;
		acb->acb_flags &= ~ACB_F_IOPDATA_OVERFLOW;
		prbuffer = arcmsr_get_iop_rqbuffer(acb);
		if (arcmsr_Read_iop_rqbuffer_data(acb, prbuffer) == 0)
			acb->acb_flags |= ACB_F_IOPDATA_OVERFLOW;
	}
	spin_unlock_irqrestore(&acb->rqbuffer_lock, flags);
	return allxfer_len;
}

void iforce_usb_xmit(struct iforce *iforce)
{
	int n, c;
	unsigned long flags;

	spin_lock_irqsave(&iforce->xmit_lock, flags);

	if (iforce->xmit.head == iforce->xmit.tail) {
		clear_bit(IFORCE_XMIT_RUNNING, iforce->xmit_flags);
		spin_unlock_irqrestore(&iforce->xmit_lock, flags);
		return;
	}

	((char *)iforce->out->transfer_buffer)[0] = iforce->xmit.buf[iforce->xmit.tail];
	XMIT_INC(iforce->xmit.tail, 1);
	n = iforce->xmit.buf[iforce->xmit.tail];
	XMIT_INC(iforce->xmit.tail, 1);

	iforce->out->transfer_buffer_length = n + 1;
	iforce->out->dev = iforce->usbdev;

	/* Copy rest of data then */
	c = CIRC_CNT_TO_END(iforce->xmit.head, iforce->xmit.tail, XMIT_SIZE);
	if (n < c) c=n;

	memcpy(iforce->out->transfer_buffer + 1,
	       &iforce->xmit.buf[iforce->xmit.tail],
	       c);
	if (n != c) {
		memcpy(iforce->out->transfer_buffer + 1 + c,
		       &iforce->xmit.buf[0],
		       n-c);
	}
	XMIT_INC(iforce->xmit.tail, n);

	if ( (n=usb_submit_urb(iforce->out, GFP_ATOMIC)) ) {
		clear_bit(IFORCE_XMIT_RUNNING, iforce->xmit_flags);
		dev_warn(&iforce->intf->dev, "usb_submit_urb failed %d\n", n);
	}

	/* The IFORCE_XMIT_RUNNING bit is not cleared here. That's intended.
	 * As long as the urb completion handler is not called, the transmiting
	 * is considered to be running */
	spin_unlock_irqrestore(&iforce->xmit_lock, flags);
}

void hsu_dma_tx(struct uart_hsu_port *up)
{
	struct circ_buf *xmit = &up->port.state->xmit;
	struct hsu_dma_buffer *dbuf = &up->txbuf;
	int count;

	/* test_and_set_bit may be better, but anyway it's in lock protected mode */
	if (up->dma_tx_on)
		return;

	/* Update the circ buf info */
	xmit->tail += dbuf->ofs;
	xmit->tail &= UART_XMIT_SIZE - 1;

	up->port.icount.tx += dbuf->ofs;
	dbuf->ofs = 0;

	/* Disable the channel */
	chan_writel(up->txc, HSU_CH_CR, 0x0);

	if (!uart_circ_empty(xmit) && !uart_tx_stopped(&up->port)) {
		dma_sync_single_for_device(up->port.dev,
					   dbuf->dma_addr,
					   dbuf->dma_size,
					   DMA_TO_DEVICE);

		count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
		dbuf->ofs = count;

		/* Reprogram the channel */
		chan_writel(up->txc, HSU_CH_D0SAR, dbuf->dma_addr + xmit->tail);
		chan_writel(up->txc, HSU_CH_D0TSR, count);

		/* Reenable the channel */
		chan_writel(up->txc, HSU_CH_DCR, 0x1
						 | (0x1 << 8)
						 | (0x1 << 16)
						 | (0x1 << 24));
		up->dma_tx_on = 1;
		chan_writel(up->txc, HSU_CH_CR, 0x1);
	}

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(&up->port);
}

static void tegra_uart_start_next_tx(struct tegra_uart_port *tup)
{
	unsigned long tail;
	unsigned long count;
	struct circ_buf *xmit = &tup->uport.state->xmit;

	tail = (unsigned long)&xmit->buf[xmit->tail];
	count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
	if (!count)
		return;

	if (count < TEGRA_UART_MIN_DMA)
		tegra_uart_start_pio_tx(tup, count);
	else if (BYTES_TO_ALIGN(tail) > 0)
		tegra_uart_start_pio_tx(tup, BYTES_TO_ALIGN(tail));
	else
		tegra_uart_start_tx_dma(tup, count);
}

/* Called with u->lock taken */
static void tegra_start_next_tx(struct tegra_uart_port *t)
{
	unsigned long tail;
	unsigned long count;
	unsigned long lsr;
	struct uart_port *u = &t->uport;

	struct circ_buf *xmit;

	xmit = &t->uport.state->xmit;
	tail = (unsigned long)&xmit->buf[xmit->tail];
	count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);


	dev_vdbg(t->uport.dev, "+%s %lu %d\n", __func__, count,
		t->tx_in_progress);

	if (count == 0) {
		if (t->is_irda && !irda_loop) {
			do {
				lsr = uart_readb(t, UART_LSR);
				if (lsr & UART_LSR_TEMT)
					break;
			} while (1);
			tegra_start_rx(u);
		}
		goto out;
	}

	if (t->is_irda && !irda_loop) {
		if (t->rx_in_progress)
			tegra_stop_rx(u);
	}

	if (!t->use_tx_dma || count < TEGRA_UART_MIN_DMA)
		tegra_start_pio_tx(t, count);
	else if (BYTES_TO_ALIGN(tail) > 0)
		tegra_start_pio_tx(t, BYTES_TO_ALIGN(tail));
	else
		tegra_start_dma_tx(t, count);

out:
	dev_vdbg(t->uport.dev, "-%s", __func__);
}

void iforce_usb_xmit(struct iforce *iforce)
{
	int n, c;
	unsigned long flags;

	spin_lock_irqsave(&iforce->xmit_lock, flags);

	if (iforce->xmit.head == iforce->xmit.tail) {
		clear_bit(IFORCE_XMIT_RUNNING, iforce->xmit_flags);
		spin_unlock_irqrestore(&iforce->xmit_lock, flags);
		return;
	}

	((char *)iforce->out->transfer_buffer)[0] = iforce->xmit.buf[iforce->xmit.tail];
	XMIT_INC(iforce->xmit.tail, 1);
	n = iforce->xmit.buf[iforce->xmit.tail];
	XMIT_INC(iforce->xmit.tail, 1);

	iforce->out->transfer_buffer_length = n + 1;
	iforce->out->dev = iforce->usbdev;

	
	c = CIRC_CNT_TO_END(iforce->xmit.head, iforce->xmit.tail, XMIT_SIZE);
	if (n < c) c=n;

	memcpy(iforce->out->transfer_buffer + 1,
	       &iforce->xmit.buf[iforce->xmit.tail],
	       c);
	if (n != c) {
		memcpy(iforce->out->transfer_buffer + 1 + c,
		       &iforce->xmit.buf[0],
		       n-c);
	}
	XMIT_INC(iforce->xmit.tail, n);

	if ( (n=usb_submit_urb(iforce->out, GFP_ATOMIC)) ) {
		clear_bit(IFORCE_XMIT_RUNNING, iforce->xmit_flags);
		dev_warn(&iforce->dev->dev, "usb_submit_urb failed %d\n", n);
	}

	spin_unlock_irqrestore(&iforce->xmit_lock, flags);
}

static int uart_read(struct bathos_pipe *pipe, char *buf, int len)
{
    struct uart_data *data = &uart_data;
    int l;

    l = min(len, CIRC_CNT_TO_END(data->cbuf.head, data->cbuf.tail,
                                 UART_BUF_SIZE));
    if (!l)
        return -EAGAIN;

    memcpy(buf, &data->buf[data->cbuf.tail], l);
    data->cbuf.tail = (data->cbuf.tail + l) & (UART_BUF_SIZE - 1);
    data->overrun = 0;

    if (CIRC_CNT(data->cbuf.head, data->cbuf.tail, UART_BUF_SIZE))
        pipe_dev_trigger_event(&__uart_dev, &evt_pipe_input_ready,
                               EVT_PRIO_MAX);

    return l;
}