atmel_serial.c

/*
 *  Driver for Atmel AT91 / AT32 Serial ports
 *  Copyright (C) 2003 Rick Bronson
 *
 *  Based on drivers/char/serial_sa1100.c, by Deep Blue Solutions Ltd.
 *  Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
 *
 *  DMA support added by Chip Coldwell.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */
#include <linux/module.h>
#include <linux/tty.h>
#include <linux/ioport.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/serial.h>
#include <linux/clk.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <linux/tty_flip.h>
#include <linux/platform_device.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/dma-mapping.h>
#include <linux/atmel_pdc.h>
#include <linux/atmel_serial.h>
#include <linux/uaccess.h>
#include <linux/platform_data/atmel.h>
#include <linux/timer.h>

#include <asm/io.h>
#include <asm/ioctls.h>

#ifdef CONFIG_ARM
#include <mach/cpu.h>
#include <asm/gpio.h>
#endif

#define PDC_BUFFER_SIZE		512
/* Revisit: We should calculate this based on the actual port settings */
#define PDC_RX_TIMEOUT		(3 * 10)		/* 3 bytes */

#if defined(CONFIG_SERIAL_ATMEL_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
#define SUPPORT_SYSRQ
#endif

#include <linux/serial_core.h>

static void atmel_start_rx(struct uart_port *port);
static void atmel_stop_rx(struct uart_port *port);

#ifdef CONFIG_SERIAL_ATMEL_TTYAT

/* Use device name ttyAT, major 204 and minor 154-169.  This is necessary if we
 * should coexist with the 8250 driver, such as if we have an external 16C550
 * UART. */
#define SERIAL_ATMEL_MAJOR	204
#define MINOR_START		154
#define ATMEL_DEVICENAME	"ttyAT"

#else

/* Use device name ttyS, major 4, minor 64-68.  This is the usual serial port
 * name, but it is legally reserved for the 8250 driver. */
#define SERIAL_ATMEL_MAJOR	TTY_MAJOR
#define MINOR_START		64
#define ATMEL_DEVICENAME	"ttyS"

#endif

#define ATMEL_ISR_PASS_LIMIT	256

/* UART registers. CR is write-only, hence no GET macro */
#define UART_PUT_CR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_CR)
#define UART_GET_MR(port)	__raw_readl((port)->membase + ATMEL_US_MR)
#define UART_PUT_MR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_MR)
#define UART_PUT_IER(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_IER)
#define UART_PUT_IDR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_IDR)
#define UART_GET_IMR(port)	__raw_readl((port)->membase + ATMEL_US_IMR)
#define UART_GET_CSR(port)	__raw_readl((port)->membase + ATMEL_US_CSR)
#define UART_GET_CHAR(port)	__raw_readl((port)->membase + ATMEL_US_RHR)
#define UART_PUT_CHAR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_THR)
#define UART_GET_BRGR(port)	__raw_readl((port)->membase + ATMEL_US_BRGR)
#define UART_PUT_BRGR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_BRGR)
#define UART_PUT_RTOR(port,v)	__raw_writel(v, (port)->membase + ATMEL_US_RTOR)
#define UART_PUT_TTGR(port, v)	__raw_writel(v, (port)->membase + ATMEL_US_TTGR)
#define UART_GET_IP_NAME(port)	__raw_readl((port)->membase + ATMEL_US_NAME)
#define UART_GET_IP_VERSION(port) __raw_readl((port)->membase + ATMEL_US_VERSION)

 /* PDC registers */
#define UART_PUT_PTCR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_PTCR)
#define UART_GET_PTSR(port)	__raw_readl((port)->membase + ATMEL_PDC_PTSR)

#define UART_PUT_RPR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_RPR)
#define UART_GET_RPR(port)	__raw_readl((port)->membase + ATMEL_PDC_RPR)
#define UART_PUT_RCR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_RCR)
#define UART_PUT_RNPR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_RNPR)
#define UART_PUT_RNCR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_RNCR)

#define UART_PUT_TPR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_TPR)
#define UART_PUT_TCR(port,v)	__raw_writel(v, (port)->membase + ATMEL_PDC_TCR)
#define UART_GET_TCR(port)	__raw_readl((port)->membase + ATMEL_PDC_TCR)

static int (*atmel_open_hook)(struct uart_port *);
static void (*atmel_close_hook)(struct uart_port *);

struct atmel_dma_buffer {
	unsigned char	*buf;
	dma_addr_t	dma_addr;
	unsigned int	dma_size;
	unsigned int	ofs;
};

struct atmel_uart_char {
	u16		status;
	u16		ch;
};

#define ATMEL_SERIAL_RINGSIZE 1024

/*
 * We wrap our port structure around the generic uart_port.
 */
struct atmel_uart_port {
	struct uart_port	uart;		/* uart */
	struct clk		*clk;		/* uart clock */
	int			may_wakeup;	/* cached value of device_may_wakeup for times we need to disable it */
	u32			backup_imr;	/* IMR saved during suspend */
	int			break_active;	/* break being received */

	bool			use_dma_rx;	/* enable DMA receiver */
	bool			use_pdc_rx;	/* enable PDC receiver */
	short			pdc_rx_idx;	/* current PDC RX buffer */
	struct atmel_dma_buffer	pdc_rx[2];	/* PDC receier */

	bool			use_dma_tx;     /* enable DMA transmitter */
	bool			use_pdc_tx;	/* enable PDC transmitter */
	struct atmel_dma_buffer	pdc_tx;		/* PDC transmitter */

	spinlock_t			lock_tx;	/* port lock */
	spinlock_t			lock_rx;	/* port lock */
	struct dma_chan			*chan_tx;
	struct dma_chan			*chan_rx;
	struct dma_async_tx_descriptor	*desc_tx;
	struct dma_async_tx_descriptor	*desc_rx;
	dma_cookie_t			cookie_tx;
	dma_cookie_t			cookie_rx;
	struct scatterlist		sg_tx;
	struct scatterlist		sg_rx;
	struct tasklet_struct	tasklet;
	unsigned int		irq_status;
	unsigned int		irq_status_prev;

	struct circ_buf		rx_ring;

	struct serial_rs485	rs485;		/* rs485 settings */
	unsigned int		tx_done_mask;
	bool			is_usart;	/* usart or uart */
	struct timer_list	uart_timer;	/* uart timer */
	int (*prepare_rx)(struct uart_port *port);
	int (*prepare_tx)(struct uart_port *port);
	void (*schedule_rx)(struct uart_port *port);
	void (*schedule_tx)(struct uart_port *port);
	void (*release_rx)(struct uart_port *port);
	void (*release_tx)(struct uart_port *port);
};

static struct atmel_uart_port atmel_ports[ATMEL_MAX_UART];
static DECLARE_BITMAP(atmel_ports_in_use, ATMEL_MAX_UART);

#ifdef SUPPORT_SYSRQ
static struct console atmel_console;
#endif

#if defined(CONFIG_OF)
static const struct of_device_id atmel_serial_dt_ids[] = {
	{ .compatible = "atmel,at91rm9200-usart" },
	{ .compatible = "atmel,at91sam9260-usart" },
	{ /* sentinel */ }
};

MODULE_DEVICE_TABLE(of, atmel_serial_dt_ids);
#endif

static inline struct atmel_uart_port *
to_atmel_uart_port(struct uart_port *uart)
{
	return container_of(uart, struct atmel_uart_port, uart);
}

#ifdef CONFIG_SERIAL_ATMEL_PDC
static bool atmel_use_pdc_rx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	return atmel_port->use_pdc_rx;
}

static bool atmel_use_pdc_tx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	return atmel_port->use_pdc_tx;
}
#else
static bool atmel_use_pdc_rx(struct uart_port *port)
{
	return false;
}

static bool atmel_use_pdc_tx(struct uart_port *port)
{
	return false;
}
#endif

static bool atmel_use_dma_tx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	return atmel_port->use_dma_tx;
}

static bool atmel_use_dma_rx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	return atmel_port->use_dma_rx;
}

/* Enable or disable the rs485 support */
void atmel_config_rs485(struct uart_port *port, struct serial_rs485 *rs485conf)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	unsigned int mode;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);

	/* Disable interrupts */
	UART_PUT_IDR(port, atmel_port->tx_done_mask);

	mode = UART_GET_MR(port);

	/* Resetting serial mode to RS232 (0x0) */
	mode &= ~ATMEL_US_USMODE;

	atmel_port->rs485 = *rs485conf;

	if (rs485conf->flags & SER_RS485_ENABLED) {
		dev_dbg(port->dev, "Setting UART to RS485\n");
		atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
		if ((rs485conf->delay_rts_after_send) > 0)
			UART_PUT_TTGR(port, rs485conf->delay_rts_after_send);
		mode |= ATMEL_US_USMODE_RS485;
	} else {
		dev_dbg(port->dev, "Setting UART to RS232\n");
		if (atmel_use_pdc_tx(port))
			atmel_port->tx_done_mask = ATMEL_US_ENDTX |
				ATMEL_US_TXBUFE;
		else
			atmel_port->tx_done_mask = ATMEL_US_TXRDY;
	}
	UART_PUT_MR(port, mode);

	/* Enable interrupts */
	UART_PUT_IER(port, atmel_port->tx_done_mask);

	spin_unlock_irqrestore(&port->lock, flags);

}

/*
 * Return TIOCSER_TEMT when transmitter FIFO and Shift register is empty.
 */
static u_int atmel_tx_empty(struct uart_port *port)
{
	return (UART_GET_CSR(port) & ATMEL_US_TXEMPTY) ? TIOCSER_TEMT : 0;
}

/*
 * Set state of the modem control output lines
 */
static void atmel_set_mctrl(struct uart_port *port, u_int mctrl)
{
	unsigned int control = 0;
	unsigned int mode;
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

#ifdef CONFIG_ARCH_AT91RM9200
	if (cpu_is_at91rm9200()) {
		/*
		 * AT91RM9200 Errata #39: RTS0 is not internally connected
		 * to PA21. We need to drive the pin manually.
		 */
		if (port->mapbase == AT91RM9200_BASE_US0) {
			if (mctrl & TIOCM_RTS)
				at91_set_gpio_value(AT91_PIN_PA21, 0);
			else
				at91_set_gpio_value(AT91_PIN_PA21, 1);
		}
	}
#endif

	if (mctrl & TIOCM_RTS)
		control |= ATMEL_US_RTSEN;
	else
		control |= ATMEL_US_RTSDIS;

	if (mctrl & TIOCM_DTR)
		control |= ATMEL_US_DTREN;
	else
		control |= ATMEL_US_DTRDIS;

	UART_PUT_CR(port, control);

	/* Local loopback mode? */
	mode = UART_GET_MR(port) & ~ATMEL_US_CHMODE;
	if (mctrl & TIOCM_LOOP)
		mode |= ATMEL_US_CHMODE_LOC_LOOP;
	else
		mode |= ATMEL_US_CHMODE_NORMAL;

	/* Resetting serial mode to RS232 (0x0) */
	mode &= ~ATMEL_US_USMODE;

	if (atmel_port->rs485.flags & SER_RS485_ENABLED) {
		dev_dbg(port->dev, "Setting UART to RS485\n");
		if ((atmel_port->rs485.delay_rts_after_send) > 0)
			UART_PUT_TTGR(port,
					atmel_port->rs485.delay_rts_after_send);
		mode |= ATMEL_US_USMODE_RS485;
	} else {
		dev_dbg(port->dev, "Setting UART to RS232\n");
	}
	UART_PUT_MR(port, mode);
}

/*
 * Get state of the modem control input lines
 */
static u_int atmel_get_mctrl(struct uart_port *port)
{
	unsigned int status, ret = 0;

	status = UART_GET_CSR(port);

	/*
	 * The control signals are active low.
	 */
	if (!(status & ATMEL_US_DCD))
		ret |= TIOCM_CD;
	if (!(status & ATMEL_US_CTS))
		ret |= TIOCM_CTS;
	if (!(status & ATMEL_US_DSR))
		ret |= TIOCM_DSR;
	if (!(status & ATMEL_US_RI))
		ret |= TIOCM_RI;

	return ret;
}

/*
 * Stop transmitting.
 */
static void atmel_stop_tx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	if (atmel_use_pdc_tx(port)) {
		/* disable PDC transmit */
		UART_PUT_PTCR(port, ATMEL_PDC_TXTDIS);
	}
	/* Disable interrupts */
	UART_PUT_IDR(port, atmel_port->tx_done_mask);

	if ((atmel_port->rs485.flags & SER_RS485_ENABLED) &&
	    !(atmel_port->rs485.flags & SER_RS485_RX_DURING_TX))
		atmel_start_rx(port);
}

/*
 * Start transmitting.
 */
static void atmel_start_tx(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	if (atmel_use_pdc_tx(port)) {
		if (UART_GET_PTSR(port) & ATMEL_PDC_TXTEN)
			/* The transmitter is already running.  Yes, we
			   really need this.*/
			return;

		if ((atmel_port->rs485.flags & SER_RS485_ENABLED) &&
		    !(atmel_port->rs485.flags & SER_RS485_RX_DURING_TX))
			atmel_stop_rx(port);

		/* re-enable PDC transmit */
		UART_PUT_PTCR(port, ATMEL_PDC_TXTEN);
	}
	/* Enable interrupts */
	UART_PUT_IER(port, atmel_port->tx_done_mask);
}

/*
 * start receiving - port is in process of being opened.
 */
static void atmel_start_rx(struct uart_port *port)
{
	UART_PUT_CR(port, ATMEL_US_RSTSTA);  /* reset status and receiver */

	UART_PUT_CR(port, ATMEL_US_RXEN);

	if (atmel_use_pdc_rx(port)) {
		/* enable PDC controller */
		UART_PUT_IER(port, ATMEL_US_ENDRX | ATMEL_US_TIMEOUT |
			port->read_status_mask);
		UART_PUT_PTCR(port, ATMEL_PDC_RXTEN);
	} else {
		UART_PUT_IER(port, ATMEL_US_RXRDY);
	}
}

/*
 * Stop receiving - port is in process of being closed.
 */
static void atmel_stop_rx(struct uart_port *port)
{
	UART_PUT_CR(port, ATMEL_US_RXDIS);

	if (atmel_use_pdc_rx(port)) {
		/* disable PDC receive */
		UART_PUT_PTCR(port, ATMEL_PDC_RXTDIS);
		UART_PUT_IDR(port, ATMEL_US_ENDRX | ATMEL_US_TIMEOUT |
			port->read_status_mask);
	} else {
		UART_PUT_IDR(port, ATMEL_US_RXRDY);
	}
}

/*
 * Enable modem status interrupts
 */
static void atmel_enable_ms(struct uart_port *port)
{
	UART_PUT_IER(port, ATMEL_US_RIIC | ATMEL_US_DSRIC
			| ATMEL_US_DCDIC | ATMEL_US_CTSIC);
}

/*
 * Control the transmission of a break signal
 */
static void atmel_break_ctl(struct uart_port *port, int break_state)
{
	if (break_state != 0)
		UART_PUT_CR(port, ATMEL_US_STTBRK);	/* start break */
	else
		UART_PUT_CR(port, ATMEL_US_STPBRK);	/* stop break */
}

/*
 * Stores the incoming character in the ring buffer
 */
static void
atmel_buffer_rx_char(struct uart_port *port, unsigned int status,
		     unsigned int ch)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct circ_buf *ring = &atmel_port->rx_ring;
	struct atmel_uart_char *c;

	if (!CIRC_SPACE(ring->head, ring->tail, ATMEL_SERIAL_RINGSIZE))
		/* Buffer overflow, ignore char */
		return;

	c = &((struct atmel_uart_char *)ring->buf)[ring->head];
	c->status	= status;
	c->ch		= ch;

	/* Make sure the character is stored before we update head. */
	smp_wmb();

	ring->head = (ring->head + 1) & (ATMEL_SERIAL_RINGSIZE - 1);
}

/*
 * Deal with parity, framing and overrun errors.
 */
static void atmel_pdc_rxerr(struct uart_port *port, unsigned int status)
{
	/* clear error */
	UART_PUT_CR(port, ATMEL_US_RSTSTA);

	if (status & ATMEL_US_RXBRK) {
		/* ignore side-effect */
		status &= ~(ATMEL_US_PARE | ATMEL_US_FRAME);
		port->icount.brk++;
	}
	if (status & ATMEL_US_PARE)
		port->icount.parity++;
	if (status & ATMEL_US_FRAME)
		port->icount.frame++;
	if (status & ATMEL_US_OVRE)
		port->icount.overrun++;
}

/*
 * Characters received (called from interrupt handler)
 */
static void atmel_rx_chars(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	unsigned int status, ch;

	status = UART_GET_CSR(port);
	while (status & ATMEL_US_RXRDY) {
		ch = UART_GET_CHAR(port);

		/*
		 * note that the error handling code is
		 * out of the main execution path
		 */
		if (unlikely(status & (ATMEL_US_PARE | ATMEL_US_FRAME
				       | ATMEL_US_OVRE | ATMEL_US_RXBRK)
			     || atmel_port->break_active)) {

			/* clear error */
			UART_PUT_CR(port, ATMEL_US_RSTSTA);

			if (status & ATMEL_US_RXBRK
			    && !atmel_port->break_active) {
				atmel_port->break_active = 1;
				UART_PUT_IER(port, ATMEL_US_RXBRK);
			} else {
				/*
				 * This is either the end-of-break
				 * condition or we've received at
				 * least one character without RXBRK
				 * being set. In both cases, the next
				 * RXBRK will indicate start-of-break.
				 */
				UART_PUT_IDR(port, ATMEL_US_RXBRK);
				status &= ~ATMEL_US_RXBRK;
				atmel_port->break_active = 0;
			}
		}

		atmel_buffer_rx_char(port, status, ch);
		status = UART_GET_CSR(port);
	}

	tasklet_schedule(&atmel_port->tasklet);
}

/*
 * Transmit characters (called from tasklet with TXRDY interrupt
 * disabled)
 */
static void atmel_tx_chars(struct uart_port *port)
{
	struct circ_buf *xmit = &port->state->xmit;
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	if (port->x_char && UART_GET_CSR(port) & atmel_port->tx_done_mask) {
		UART_PUT_CHAR(port, port->x_char);
		port->icount.tx++;
		port->x_char = 0;
	}
	if (uart_circ_empty(xmit) || uart_tx_stopped(port))
		return;

	while (UART_GET_CSR(port) & atmel_port->tx_done_mask) {
		UART_PUT_CHAR(port, xmit->buf[xmit->tail]);
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		port->icount.tx++;
		if (uart_circ_empty(xmit))
			break;
	}

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(port);

	if (!uart_circ_empty(xmit))
		/* Enable interrupts */
		UART_PUT_IER(port, atmel_port->tx_done_mask);
}

static void atmel_complete_tx_dma(void *arg)
{
	struct atmel_uart_port *atmel_port = arg;
	struct uart_port *port = &atmel_port->uart;
	struct circ_buf *xmit = &port->state->xmit;
	struct dma_chan *chan = atmel_port->chan_tx;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);

	if (chan)
		dmaengine_terminate_all(chan);
	xmit->tail += sg_dma_len(&atmel_port->sg_tx);
	xmit->tail &= UART_XMIT_SIZE - 1;

	port->icount.tx += sg_dma_len(&atmel_port->sg_tx);

	spin_lock_irq(&atmel_port->lock_tx);
	async_tx_ack(atmel_port->desc_tx);
	atmel_port->cookie_tx = -EINVAL;
	atmel_port->desc_tx = NULL;
	spin_unlock_irq(&atmel_port->lock_tx);

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(port);

	/* Do we really need this? */
	if (!uart_circ_empty(xmit))
		tasklet_schedule(&atmel_port->tasklet);

	spin_unlock_irqrestore(&port->lock, flags);
}

static void atmel_release_tx_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct dma_chan *chan = atmel_port->chan_tx;

	if (chan) {
		dmaengine_terminate_all(chan);
		dma_release_channel(chan);
		dma_unmap_sg(port->dev, &atmel_port->sg_tx, 1,
				DMA_MEM_TO_DEV);
	}

	atmel_port->desc_tx = NULL;
	atmel_port->chan_tx = NULL;
	atmel_port->cookie_tx = -EINVAL;
}

/*
 * Called from tasklet with TXRDY interrupt is disabled.
 */
static void atmel_tx_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct circ_buf *xmit = &port->state->xmit;
	struct dma_chan *chan = atmel_port->chan_tx;
	struct dma_async_tx_descriptor *desc;
	struct scatterlist *sg = &atmel_port->sg_tx;

	/* Make sure we have an idle channel */
	if (atmel_port->desc_tx != NULL)
		return;

	if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
		/*
		 * DMA is idle now.
		 * Port xmit buffer is already mapped,
		 * and it is one page... Just adjust
		 * offsets and lengths. Since it is a circular buffer,
		 * we have to transmit till the end, and then the rest.
		 * Take the port lock to get a
		 * consistent xmit buffer state.
		 */
		sg->offset = xmit->tail & (UART_XMIT_SIZE - 1);
		sg_dma_address(sg) = (sg_dma_address(sg) &
					~(UART_XMIT_SIZE - 1))
					+ sg->offset;
		sg_dma_len(sg) = CIRC_CNT_TO_END(xmit->head,
						xmit->tail,
						UART_XMIT_SIZE);
		BUG_ON(!sg_dma_len(sg));

		desc = dmaengine_prep_slave_sg(chan,
						sg,
						1,
						DMA_MEM_TO_DEV,
						DMA_PREP_INTERRUPT |
						DMA_CTRL_ACK);
		if (!desc) {
			dev_err(port->dev, "Failed to send via dma!\n");
			return;
		}

		dma_sync_sg_for_device(port->dev, sg, 1, DMA_MEM_TO_DEV);

		atmel_port->desc_tx = desc;
		desc->callback = atmel_complete_tx_dma;
		desc->callback_param = atmel_port;
		atmel_port->cookie_tx = dmaengine_submit(desc);

	} else {
		if (atmel_port->rs485.flags & SER_RS485_ENABLED) {
			/* DMA done, stop TX, start RX for RS485 */
			atmel_start_rx(port);
		}
	}

	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(port);
}

static int atmel_prepare_tx_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	dma_cap_mask_t		mask;
	struct dma_slave_config config;
	int ret, nent;

	dma_cap_zero(mask);
	dma_cap_set(DMA_SLAVE, mask);

	atmel_port->chan_tx = dma_request_slave_channel(port->dev, "tx");
	if (atmel_port->chan_tx == NULL)
		goto chan_err;
	dev_info(port->dev, "using %s for tx DMA transfers\n",
		dma_chan_name(atmel_port->chan_tx));

	spin_lock_init(&atmel_port->lock_tx);
	sg_init_table(&atmel_port->sg_tx, 1);
	/* UART circular tx buffer is an aligned page. */
	BUG_ON((int)port->state->xmit.buf & ~PAGE_MASK);
	sg_set_page(&atmel_port->sg_tx,
			virt_to_page(port->state->xmit.buf),
			UART_XMIT_SIZE,
			(int)port->state->xmit.buf & ~PAGE_MASK);
	nent = dma_map_sg(port->dev,
				&atmel_port->sg_tx,
				1,
				DMA_MEM_TO_DEV);

	if (!nent) {
		dev_dbg(port->dev, "need to release resource of dma\n");
		goto chan_err;
	} else {
		dev_dbg(port->dev, "%s: mapped %d@%p to %x\n", __func__,
			sg_dma_len(&atmel_port->sg_tx),
			port->state->xmit.buf,
			sg_dma_address(&atmel_port->sg_tx));
	}

	/* Configure the slave DMA */
	memset(&config, 0, sizeof(config));
	config.direction = DMA_MEM_TO_DEV;
	config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	config.dst_addr = port->mapbase + ATMEL_US_THR;

	ret = dmaengine_device_control(atmel_port->chan_tx,
					DMA_SLAVE_CONFIG,
					(unsigned long)&config);
	if (ret) {
		dev_err(port->dev, "DMA tx slave configuration failed\n");
		goto chan_err;
	}

	return 0;

chan_err:
	dev_err(port->dev, "TX channel not available, switch to pio\n");
	atmel_port->use_dma_tx = 0;
	if (atmel_port->chan_tx)
		atmel_release_tx_dma(port);
	return -EINVAL;
}

static void atmel_flip_buffer_rx_dma(struct uart_port *port,
					char *buf, size_t count)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct tty_port *tport = &port->state->port;

	dma_sync_sg_for_cpu(port->dev,
				&atmel_port->sg_rx,
				1,
				DMA_DEV_TO_MEM);

	tty_insert_flip_string(tport, buf, count);

	dma_sync_sg_for_device(port->dev,
				&atmel_port->sg_rx,
				1,
				DMA_DEV_TO_MEM);
	/*
	 * Drop the lock here since it might end up calling
	 * uart_start(), which takes the lock.
	 */
	spin_unlock(&port->lock);
	tty_flip_buffer_push(tport);
	spin_lock(&port->lock);
}

static void atmel_complete_rx_dma(void *arg)
{
	struct uart_port *port = arg;
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	tasklet_schedule(&atmel_port->tasklet);
}

static void atmel_release_rx_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct dma_chan *chan = atmel_port->chan_rx;

	if (chan) {
		dmaengine_terminate_all(chan);
		dma_release_channel(chan);
		dma_unmap_sg(port->dev, &atmel_port->sg_rx, 1,
				DMA_DEV_TO_MEM);
	}

	atmel_port->desc_rx = NULL;
	atmel_port->chan_rx = NULL;
	atmel_port->cookie_rx = -EINVAL;

	if (!atmel_port->is_usart)
		del_timer_sync(&atmel_port->uart_timer);
}

static void atmel_rx_from_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct circ_buf *ring = &atmel_port->rx_ring;
	struct dma_chan *chan = atmel_port->chan_rx;
	struct dma_tx_state state;
	enum dma_status dmastat;
	size_t pending, count;


	/* Reset the UART timeout early so that we don't miss one */
	UART_PUT_CR(port, ATMEL_US_STTTO);
	dmastat = dmaengine_tx_status(chan,
				atmel_port->cookie_rx,
				&state);
	/* Restart a new tasklet if DMA status is error */
	if (dmastat == DMA_ERROR) {
		dev_dbg(port->dev, "Get residue error, restart tasklet\n");
		UART_PUT_IER(port, ATMEL_US_TIMEOUT);
		tasklet_schedule(&atmel_port->tasklet);
		return;
	}
	/* current transfer size should no larger than dma buffer */
	pending = sg_dma_len(&atmel_port->sg_rx) - state.residue;
	BUG_ON(pending > sg_dma_len(&atmel_port->sg_rx));

	/*
	 * This will take the chars we have so far,
	 * ring->head will record the transfer size, only new bytes come
	 * will insert into the framework.
	 */
	if (pending > ring->head) {
		count = pending - ring->head;

		atmel_flip_buffer_rx_dma(port, ring->buf + ring->head, count);

		ring->head += count;
		if (ring->head == sg_dma_len(&atmel_port->sg_rx))
			ring->head = 0;

		port->icount.rx += count;
	}

	UART_PUT_IER(port, ATMEL_US_TIMEOUT);
}

static int atmel_prepare_rx_dma(struct uart_port *port)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
	struct dma_async_tx_descriptor *desc;
	dma_cap_mask_t		mask;
	struct dma_slave_config config;
	struct circ_buf		*ring;
	int ret, nent;

	ring = &atmel_port->rx_ring;

	dma_cap_zero(mask);
	dma_cap_set(DMA_CYCLIC, mask);

	atmel_port->chan_rx = dma_request_slave_channel(port->dev, "rx");
	if (atmel_port->chan_rx == NULL)
		goto chan_err;
	dev_info(port->dev, "using %s for rx DMA transfers\n",
		dma_chan_name(atmel_port->chan_rx));

	spin_lock_init(&atmel_port->lock_rx);
	sg_init_table(&atmel_port->sg_rx, 1);
	/* UART circular rx buffer is an aligned page. */
	BUG_ON((int)port->state->xmit.buf & ~PAGE_MASK);
	sg_set_page(&atmel_port->sg_rx,
			virt_to_page(ring->buf),
			ATMEL_SERIAL_RINGSIZE,
			(int)ring->buf & ~PAGE_MASK);
			nent = dma_map_sg(port->dev,
					&atmel_port->sg_rx,
					1,
					DMA_DEV_TO_MEM);

	if (!nent) {
		dev_dbg(port->dev, "need to release resource of dma\n");
		goto chan_err;
	} else {
		dev_dbg(port->dev, "%s: mapped %d@%p to %x\n", __func__,
			sg_dma_len(&atmel_port->sg_rx),
			ring->buf,
			sg_dma_address(&atmel_port->sg_rx));
	}

	/* Configure the slave DMA */
	memset(&config, 0, sizeof(config));
	config.direction = DMA_DEV_TO_MEM;
	config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
	config.src_addr = port->mapbase + ATMEL_US_RHR;

	ret = dmaengine_device_control(atmel_port->chan_rx,
					DMA_SLAVE_CONFIG,
					(unsigned long)&config);
	if (ret) {
		dev_err(port->dev, "DMA rx slave configuration failed\n");
		goto chan_err;
	}
	/*
	 * Prepare a cyclic dma transfer, assign 2 descriptors,
	 * each one is half ring buffer size
	 */
	desc = dmaengine_prep_dma_cyclic(atmel_port->chan_rx,
				sg_dma_address(&atmel_port->sg_rx),
				sg_dma_len(&atmel_port->sg_rx),
				sg_dma_len(&atmel_port->sg_rx)/2,
				DMA_DEV_TO_MEM,
				DMA_PREP_INTERRUPT);
	desc->callback = atmel_complete_rx_dma;
	desc->callback_param = port;
	atmel_port->desc_rx = desc;
	atmel_port->cookie_rx = dmaengine_submit(desc);

	return 0;

chan_err:
	dev_err(port->dev, "RX channel not available, switch to pio\n");
	atmel_port->use_dma_rx = 0;
	if (atmel_port->chan_rx)
		atmel_release_rx_dma(port);
	return -EINVAL;
}

static void atmel_uart_timer_callback(unsigned long data)
{
	struct uart_port *port = (void *)data;
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	tasklet_schedule(&atmel_port->tasklet);
	mod_timer(&atmel_port->uart_timer, jiffies + uart_poll_timeout(port));
}

/*
 * receive interrupt handler.
 */
static void
atmel_handle_receive(struct uart_port *port, unsigned int pending)
{
	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);

	if (atmel_use_pdc_rx(port)) {
		/*
		 * PDC receive. Just schedule the tasklet and let it
		 * figure out the details.
		 *
		 * TODO: We're not handling error flags correctly at
		 * the moment.
		 */
		if (pending & (ATMEL_US_ENDRX | ATMEL_US_TIMEOUT)) {
			UART_PUT_IDR(port, (ATMEL_US_ENDRX
						| ATMEL_US_TIMEOUT));
			tasklet_schedule(&atmel_port->tasklet);
		}

		if (pending & (ATMEL_US_RXBRK | ATMEL_US_OVRE |
				ATMEL_US_FRAME | ATMEL_US_PARE))
			atmel_pdc_rxerr(port, pending);
	}

	if (atmel_use_dma_rx(port)) {
		if (pending & ATMEL_US_TIMEOUT) {
			UART_PUT_IDR(port, ATMEL_US_TIMEOUT);
			tasklet_schedule(&atmel_port->tasklet);
		}