imx.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Driver for Motorola/Freescale IMX serial ports
 *
 * Based on drivers/char/serial.c, by Linus Torvalds, Theodore Ts'o.
 *
 * Author: Sascha Hauer <sascha@saschahauer.de>
 * Copyright (C) 2004 Pengutronix
 */

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

#include <linux/module.h>
#include <linux/ioport.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/sysrq.h>
#include <linux/platform_device.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/serial_core.h>
#include <linux/serial.h>
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/pinctrl/consumer.h>
#include <linux/rational.h>
#include <linux/slab.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/io.h>
#include <linux/dma-mapping.h>

#include <asm/irq.h>
#include <linux/platform_data/serial-imx.h>
#include <linux/platform_data/dma-imx.h>

#include "serial_mctrl_gpio.h"

/* Register definitions */
#define URXD0 0x0  /* Receiver Register */
#define URTX0 0x40 /* Transmitter Register */
#define UCR1  0x80 /* Control Register 1 */
#define UCR2  0x84 /* Control Register 2 */
#define UCR3  0x88 /* Control Register 3 */
#define UCR4  0x8c /* Control Register 4 */
#define UFCR  0x90 /* FIFO Control Register */
#define USR1  0x94 /* Status Register 1 */
#define USR2  0x98 /* Status Register 2 */
#define UESC  0x9c /* Escape Character Register */
#define UTIM  0xa0 /* Escape Timer Register */
#define UBIR  0xa4 /* BRM Incremental Register */
#define UBMR  0xa8 /* BRM Modulator Register */
#define UBRC  0xac /* Baud Rate Count Register */
#define IMX21_ONEMS 0xb0 /* One Millisecond register */
#define IMX1_UTS 0xd0 /* UART Test Register on i.mx1 */
#define IMX21_UTS 0xb4 /* UART Test Register on all other i.mx*/

/* UART Control Register Bit Fields.*/
#define URXD_DUMMY_READ (1<<16)
#define URXD_CHARRDY	(1<<15)
#define URXD_ERR	(1<<14)
#define URXD_OVRRUN	(1<<13)
#define URXD_FRMERR	(1<<12)
#define URXD_BRK	(1<<11)
#define URXD_PRERR	(1<<10)
#define URXD_RX_DATA	(0xFF<<0)
#define UCR1_ADEN	(1<<15) /* Auto detect interrupt */
#define UCR1_ADBR	(1<<14) /* Auto detect baud rate */
#define UCR1_TRDYEN	(1<<13) /* Transmitter ready interrupt enable */
#define UCR1_IDEN	(1<<12) /* Idle condition interrupt */
#define UCR1_ICD_REG(x) (((x) & 3) << 10) /* idle condition detect */
#define UCR1_RRDYEN	(1<<9)	/* Recv ready interrupt enable */
#define UCR1_RXDMAEN	(1<<8)	/* Recv ready DMA enable */
#define UCR1_IREN	(1<<7)	/* Infrared interface enable */
#define UCR1_TXMPTYEN	(1<<6)	/* Transimitter empty interrupt enable */
#define UCR1_RTSDEN	(1<<5)	/* RTS delta interrupt enable */
#define UCR1_SNDBRK	(1<<4)	/* Send break */
#define UCR1_TXDMAEN	(1<<3)	/* Transmitter ready DMA enable */
#define IMX1_UCR1_UARTCLKEN (1<<2) /* UART clock enabled, i.mx1 only */
#define UCR1_ATDMAEN    (1<<2)  /* Aging DMA Timer Enable */
#define UCR1_DOZE	(1<<1)	/* Doze */
#define UCR1_UARTEN	(1<<0)	/* UART enabled */
#define UCR2_ESCI	(1<<15)	/* Escape seq interrupt enable */
#define UCR2_IRTS	(1<<14)	/* Ignore RTS pin */
#define UCR2_CTSC	(1<<13)	/* CTS pin control */
#define UCR2_CTS	(1<<12)	/* Clear to send */
#define UCR2_ESCEN	(1<<11)	/* Escape enable */
#define UCR2_PREN	(1<<8)	/* Parity enable */
#define UCR2_PROE	(1<<7)	/* Parity odd/even */
#define UCR2_STPB	(1<<6)	/* Stop */
#define UCR2_WS		(1<<5)	/* Word size */
#define UCR2_RTSEN	(1<<4)	/* Request to send interrupt enable */
#define UCR2_ATEN	(1<<3)	/* Aging Timer Enable */
#define UCR2_TXEN	(1<<2)	/* Transmitter enabled */
#define UCR2_RXEN	(1<<1)	/* Receiver enabled */
#define UCR2_SRST	(1<<0)	/* SW reset */
#define UCR3_DTREN	(1<<13) /* DTR interrupt enable */
#define UCR3_PARERREN	(1<<12) /* Parity enable */
#define UCR3_FRAERREN	(1<<11) /* Frame error interrupt enable */
#define UCR3_DSR	(1<<10) /* Data set ready */
#define UCR3_DCD	(1<<9)	/* Data carrier detect */
#define UCR3_RI		(1<<8)	/* Ring indicator */
#define UCR3_ADNIMP	(1<<7)	/* Autobaud Detection Not Improved */
#define UCR3_RXDSEN	(1<<6)	/* Receive status interrupt enable */
#define UCR3_AIRINTEN	(1<<5)	/* Async IR wake interrupt enable */
#define UCR3_AWAKEN	(1<<4)	/* Async wake interrupt enable */
#define UCR3_DTRDEN	(1<<3)	/* Data Terminal Ready Delta Enable. */
#define IMX21_UCR3_RXDMUXSEL	(1<<2)	/* RXD Muxed Input Select */
#define UCR3_INVT	(1<<1)	/* Inverted Infrared transmission */
#define UCR3_BPEN	(1<<0)	/* Preset registers enable */
#define UCR4_CTSTL_SHF	10	/* CTS trigger level shift */
#define UCR4_CTSTL_MASK	0x3F	/* CTS trigger is 6 bits wide */
#define UCR4_INVR	(1<<9)	/* Inverted infrared reception */
#define UCR4_ENIRI	(1<<8)	/* Serial infrared interrupt enable */
#define UCR4_WKEN	(1<<7)	/* Wake interrupt enable */
#define UCR4_REF16	(1<<6)	/* Ref freq 16 MHz */
#define UCR4_IDDMAEN    (1<<6)  /* DMA IDLE Condition Detected */
#define UCR4_IRSC	(1<<5)	/* IR special case */
#define UCR4_TCEN	(1<<3)	/* Transmit complete interrupt enable */
#define UCR4_BKEN	(1<<2)	/* Break condition interrupt enable */
#define UCR4_OREN	(1<<1)	/* Receiver overrun interrupt enable */
#define UCR4_DREN	(1<<0)	/* Recv data ready interrupt enable */
#define UFCR_RXTL_SHF	0	/* Receiver trigger level shift */
#define UFCR_DCEDTE	(1<<6)	/* DCE/DTE mode select */
#define UFCR_RFDIV	(7<<7)	/* Reference freq divider mask */
#define UFCR_RFDIV_REG(x)	(((x) < 7 ? 6 - (x) : 6) << 7)
#define UFCR_TXTL_SHF	10	/* Transmitter trigger level shift */
#define USR1_PARITYERR	(1<<15) /* Parity error interrupt flag */
#define USR1_RTSS	(1<<14) /* RTS pin status */
#define USR1_TRDY	(1<<13) /* Transmitter ready interrupt/dma flag */
#define USR1_RTSD	(1<<12) /* RTS delta */
#define USR1_ESCF	(1<<11) /* Escape seq interrupt flag */
#define USR1_FRAMERR	(1<<10) /* Frame error interrupt flag */
#define USR1_RRDY	(1<<9)	 /* Receiver ready interrupt/dma flag */
#define USR1_AGTIM	(1<<8)	 /* Ageing timer interrupt flag */
#define USR1_DTRD	(1<<7)	 /* DTR Delta */
#define USR1_RXDS	 (1<<6)	 /* Receiver idle interrupt flag */
#define USR1_AIRINT	 (1<<5)	 /* Async IR wake interrupt flag */
#define USR1_AWAKE	 (1<<4)	 /* Aysnc wake interrupt flag */
#define USR2_ADET	 (1<<15) /* Auto baud rate detect complete */
#define USR2_TXFE	 (1<<14) /* Transmit buffer FIFO empty */
#define USR2_DTRF	 (1<<13) /* DTR edge interrupt flag */
#define USR2_IDLE	 (1<<12) /* Idle condition */
#define USR2_RIDELT	 (1<<10) /* Ring Interrupt Delta */
#define USR2_RIIN	 (1<<9)	 /* Ring Indicator Input */
#define USR2_IRINT	 (1<<8)	 /* Serial infrared interrupt flag */
#define USR2_WAKE	 (1<<7)	 /* Wake */
#define USR2_DCDIN	 (1<<5)	 /* Data Carrier Detect Input */
#define USR2_RTSF	 (1<<4)	 /* RTS edge interrupt flag */
#define USR2_TXDC	 (1<<3)	 /* Transmitter complete */
#define USR2_BRCD	 (1<<2)	 /* Break condition */
#define USR2_ORE	(1<<1)	 /* Overrun error */
#define USR2_RDR	(1<<0)	 /* Recv data ready */
#define UTS_FRCPERR	(1<<13) /* Force parity error */
#define UTS_LOOP	(1<<12)	 /* Loop tx and rx */
#define UTS_TXEMPTY	 (1<<6)	 /* TxFIFO empty */
#define UTS_RXEMPTY	 (1<<5)	 /* RxFIFO empty */
#define UTS_TXFULL	 (1<<4)	 /* TxFIFO full */
#define UTS_RXFULL	 (1<<3)	 /* RxFIFO full */
#define UTS_SOFTRST	 (1<<0)	 /* Software reset */

/* We've been assigned a range on the "Low-density serial ports" major */
#define SERIAL_IMX_MAJOR	207
#define MINOR_START		16
#define DEV_NAME		"ttymxc"

/*
 * This determines how often we check the modem status signals
 * for any change.  They generally aren't connected to an IRQ
 * so we have to poll them.  We also check immediately before
 * filling the TX fifo incase CTS has been dropped.
 */
#define MCTRL_TIMEOUT	(250*HZ/1000)

#define DRIVER_NAME "IMX-uart"

#define UART_NR 8

/* i.MX21 type uart runs on all i.mx except i.MX1 and i.MX6q */
enum imx_uart_type {
	IMX1_UART,
	IMX21_UART,
	IMX53_UART,
	IMX6Q_UART,
};

/* device type dependent stuff */
struct imx_uart_data {
	unsigned uts_reg;
	enum imx_uart_type devtype;
};

struct imx_port {
	struct uart_port	port;
	struct timer_list	timer;
	unsigned int		old_status;
	unsigned int		have_rtscts:1;
	unsigned int		have_rtsgpio:1;
	unsigned int		dte_mode:1;
	struct clk		*clk_ipg;
	struct clk		*clk_per;
	const struct imx_uart_data *devdata;

	struct mctrl_gpios *gpios;

	/* shadow registers */
	unsigned int ucr1;
	unsigned int ucr2;
	unsigned int ucr3;
	unsigned int ucr4;
	unsigned int ufcr;

	/* DMA fields */
	unsigned int		dma_is_enabled:1;
	unsigned int		dma_is_rxing:1;
	unsigned int		dma_is_txing:1;
	struct dma_chan		*dma_chan_rx, *dma_chan_tx;
	struct scatterlist	rx_sgl, tx_sgl[2];
	void			*rx_buf;
	struct circ_buf		rx_ring;
	unsigned int		rx_periods;
	dma_cookie_t		rx_cookie;
	unsigned int		tx_bytes;
	unsigned int		dma_tx_nents;
	unsigned int            saved_reg[10];
	bool			context_saved;
};

struct imx_port_ucrs {
	unsigned int	ucr1;
	unsigned int	ucr2;
	unsigned int	ucr3;
};

static struct imx_uart_data imx_uart_devdata[] = {
	[IMX1_UART] = {
		.uts_reg = IMX1_UTS,
		.devtype = IMX1_UART,
	},
	[IMX21_UART] = {
		.uts_reg = IMX21_UTS,
		.devtype = IMX21_UART,
	},
	[IMX53_UART] = {
		.uts_reg = IMX21_UTS,
		.devtype = IMX53_UART,
	},
	[IMX6Q_UART] = {
		.uts_reg = IMX21_UTS,
		.devtype = IMX6Q_UART,
	},
};

static const struct platform_device_id imx_uart_devtype[] = {
	{
		.name = "imx1-uart",
		.driver_data = (kernel_ulong_t) &imx_uart_devdata[IMX1_UART],
	}, {
		.name = "imx21-uart",
		.driver_data = (kernel_ulong_t) &imx_uart_devdata[IMX21_UART],
	}, {
		.name = "imx53-uart",
		.driver_data = (kernel_ulong_t) &imx_uart_devdata[IMX53_UART],
	}, {
		.name = "imx6q-uart",
		.driver_data = (kernel_ulong_t) &imx_uart_devdata[IMX6Q_UART],
	}, {
		/* sentinel */
	}
};
MODULE_DEVICE_TABLE(platform, imx_uart_devtype);

static const struct of_device_id imx_uart_dt_ids[] = {
	{ .compatible = "fsl,imx6q-uart", .data = &imx_uart_devdata[IMX6Q_UART], },
	{ .compatible = "fsl,imx53-uart", .data = &imx_uart_devdata[IMX53_UART], },
	{ .compatible = "fsl,imx1-uart", .data = &imx_uart_devdata[IMX1_UART], },
	{ .compatible = "fsl,imx21-uart", .data = &imx_uart_devdata[IMX21_UART], },
	{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, imx_uart_dt_ids);

static void imx_uart_writel(struct imx_port *sport, u32 val, u32 offset)
{
	switch (offset) {
	case UCR1:
		sport->ucr1 = val;
		break;
	case UCR2:
		sport->ucr2 = val;
		break;
	case UCR3:
		sport->ucr3 = val;
		break;
	case UCR4:
		sport->ucr4 = val;
		break;
	case UFCR:
		sport->ufcr = val;
		break;
	default:
		break;
	}
	writel(val, sport->port.membase + offset);
}

static u32 imx_uart_readl(struct imx_port *sport, u32 offset)
{
	switch (offset) {
	case UCR1:
		return sport->ucr1;
		break;
	case UCR2:
		/*
		 * UCR2_SRST is the only bit in the cached registers that might
		 * differ from the value that was last written. As it only
		 * automatically becomes one after being cleared, reread
		 * conditionally.
		 */
		if (!(sport->ucr2 & UCR2_SRST))
			sport->ucr2 = readl(sport->port.membase + offset);
		return sport->ucr2;
		break;
	case UCR3:
		return sport->ucr3;
		break;
	case UCR4:
		return sport->ucr4;
		break;
	case UFCR:
		return sport->ufcr;
		break;
	default:
		return readl(sport->port.membase + offset);
	}
}

static inline unsigned imx_uart_uts_reg(struct imx_port *sport)
{
	return sport->devdata->uts_reg;
}

static inline int imx_uart_is_imx1(struct imx_port *sport)
{
	return sport->devdata->devtype == IMX1_UART;
}

static inline int imx_uart_is_imx21(struct imx_port *sport)
{
	return sport->devdata->devtype == IMX21_UART;
}

static inline int imx_uart_is_imx53(struct imx_port *sport)
{
	return sport->devdata->devtype == IMX53_UART;
}

static inline int imx_uart_is_imx6q(struct imx_port *sport)
{
	return sport->devdata->devtype == IMX6Q_UART;
}
/*
 * Save and restore functions for UCR1, UCR2 and UCR3 registers
 */
#if defined(CONFIG_SERIAL_IMX_CONSOLE)
static void imx_uart_ucrs_save(struct imx_port *sport,
			       struct imx_port_ucrs *ucr)
{
	/* save control registers */
	ucr->ucr1 = imx_uart_readl(sport, UCR1);
	ucr->ucr2 = imx_uart_readl(sport, UCR2);
	ucr->ucr3 = imx_uart_readl(sport, UCR3);
}

static void imx_uart_ucrs_restore(struct imx_port *sport,
				  struct imx_port_ucrs *ucr)
{
	/* restore control registers */
	imx_uart_writel(sport, ucr->ucr1, UCR1);
	imx_uart_writel(sport, ucr->ucr2, UCR2);
	imx_uart_writel(sport, ucr->ucr3, UCR3);
}
#endif

static void imx_uart_rts_active(struct imx_port *sport, u32 *ucr2)
{
	*ucr2 &= ~(UCR2_CTSC | UCR2_CTS);

	sport->port.mctrl |= TIOCM_RTS;
	mctrl_gpio_set(sport->gpios, sport->port.mctrl);
}

static void imx_uart_rts_inactive(struct imx_port *sport, u32 *ucr2)
{
	*ucr2 &= ~UCR2_CTSC;
	*ucr2 |= UCR2_CTS;

	sport->port.mctrl &= ~TIOCM_RTS;
	mctrl_gpio_set(sport->gpios, sport->port.mctrl);
}

static void imx_uart_rts_auto(struct imx_port *sport, u32 *ucr2)
{
	*ucr2 |= UCR2_CTSC;
}

/* called with port.lock taken and irqs off */
static void imx_uart_start_rx(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	unsigned int ucr1, ucr2;

	ucr1 = imx_uart_readl(sport, UCR1);
	ucr2 = imx_uart_readl(sport, UCR2);

	ucr2 |= UCR2_RXEN;

	if (sport->dma_is_enabled) {
		ucr1 |= UCR1_RXDMAEN | UCR1_ATDMAEN;
	} else {
		ucr1 |= UCR1_RRDYEN;
		ucr2 |= UCR2_ATEN;
	}

	/* Write UCR2 first as it includes RXEN */
	imx_uart_writel(sport, ucr2, UCR2);
	imx_uart_writel(sport, ucr1, UCR1);
}

/* called with port.lock taken and irqs off */
static void imx_uart_stop_tx(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	u32 ucr1;

	/*
	 * We are maybe in the SMP context, so if the DMA TX thread is running
	 * on other cpu, we have to wait for it to finish.
	 */
	if (sport->dma_is_txing)
		return;

	ucr1 = imx_uart_readl(sport, UCR1);
	imx_uart_writel(sport, ucr1 & ~UCR1_TXMPTYEN, UCR1);

	/* in rs485 mode disable transmitter if shifter is empty */
	if (port->rs485.flags & SER_RS485_ENABLED &&
	    imx_uart_readl(sport, USR2) & USR2_TXDC) {
		u32 ucr2 = imx_uart_readl(sport, UCR2), ucr4;
		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
			imx_uart_rts_active(sport, &ucr2);
		else
			imx_uart_rts_inactive(sport, &ucr2);
		imx_uart_writel(sport, ucr2, UCR2);

		imx_uart_start_rx(port);

		ucr4 = imx_uart_readl(sport, UCR4);
		ucr4 &= ~UCR4_TCEN;
		imx_uart_writel(sport, ucr4, UCR4);
	}
}

/* called with port.lock taken and irqs off */
static void imx_uart_stop_rx(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	u32 ucr1, ucr2;

	ucr1 = imx_uart_readl(sport, UCR1);
	ucr2 = imx_uart_readl(sport, UCR2);

	if (sport->dma_is_enabled) {
		ucr1 &= ~(UCR1_RXDMAEN | UCR1_ATDMAEN);
	} else {
		ucr1 &= ~UCR1_RRDYEN;
		ucr2 &= ~UCR2_ATEN;
	}
	imx_uart_writel(sport, ucr1, UCR1);

	ucr2 &= ~UCR2_RXEN;
	imx_uart_writel(sport, ucr2, UCR2);
}

/* called with port.lock taken and irqs off */
static void imx_uart_enable_ms(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;

	mod_timer(&sport->timer, jiffies);

	mctrl_gpio_enable_ms(sport->gpios);
}

static void imx_uart_dma_tx(struct imx_port *sport);

/* called with port.lock taken and irqs off */
static inline void imx_uart_transmit_buffer(struct imx_port *sport)
{
	struct circ_buf *xmit = &sport->port.state->xmit;

	if (sport->port.x_char) {
		/* Send next char */
		imx_uart_writel(sport, sport->port.x_char, URTX0);
		sport->port.icount.tx++;
		sport->port.x_char = 0;
		return;
	}

	if (uart_circ_empty(xmit) || uart_tx_stopped(&sport->port)) {
		imx_uart_stop_tx(&sport->port);
		return;
	}

	if (sport->dma_is_enabled) {
		u32 ucr1;
		/*
		 * We've just sent a X-char Ensure the TX DMA is enabled
		 * and the TX IRQ is disabled.
		 **/
		ucr1 = imx_uart_readl(sport, UCR1);
		ucr1 &= ~UCR1_TXMPTYEN;
		if (sport->dma_is_txing) {
			ucr1 |= UCR1_TXDMAEN;
			imx_uart_writel(sport, ucr1, UCR1);
		} else {
			imx_uart_writel(sport, ucr1, UCR1);
			imx_uart_dma_tx(sport);
		}

		return;
	}

	while (!uart_circ_empty(xmit) &&
	       !(imx_uart_readl(sport, imx_uart_uts_reg(sport)) & UTS_TXFULL)) {
		/* send xmit->buf[xmit->tail]
		 * out the port here */
		imx_uart_writel(sport, xmit->buf[xmit->tail], URTX0);
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		sport->port.icount.tx++;
	}

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

	if (uart_circ_empty(xmit))
		imx_uart_stop_tx(&sport->port);
}

static void imx_uart_dma_tx_callback(void *data)
{
	struct imx_port *sport = data;
	struct scatterlist *sgl = &sport->tx_sgl[0];
	struct circ_buf *xmit = &sport->port.state->xmit;
	unsigned long flags;
	u32 ucr1;

	spin_lock_irqsave(&sport->port.lock, flags);

	dma_unmap_sg(sport->port.dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);

	ucr1 = imx_uart_readl(sport, UCR1);
	ucr1 &= ~UCR1_TXDMAEN;
	imx_uart_writel(sport, ucr1, UCR1);

	/* update the stat */
	xmit->tail = (xmit->tail + sport->tx_bytes) & (UART_XMIT_SIZE - 1);
	sport->port.icount.tx += sport->tx_bytes;

	dev_dbg(sport->port.dev, "we finish the TX DMA.\n");

	sport->dma_is_txing = 0;

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

	if (!uart_circ_empty(xmit) && !uart_tx_stopped(&sport->port))
		imx_uart_dma_tx(sport);
	else if (sport->port.rs485.flags & SER_RS485_ENABLED) {
		u32 ucr4 = imx_uart_readl(sport, UCR4);
		ucr4 |= UCR4_TCEN;
		imx_uart_writel(sport, ucr4, UCR4);
	}

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

/* called with port.lock taken and irqs off */
static void imx_uart_dma_tx(struct imx_port *sport)
{
	struct circ_buf *xmit = &sport->port.state->xmit;
	struct scatterlist *sgl = sport->tx_sgl;
	struct dma_async_tx_descriptor *desc;
	struct dma_chan	*chan = sport->dma_chan_tx;
	struct device *dev = sport->port.dev;
	u32 ucr1, ucr4;
	int ret;

	if (sport->dma_is_txing)
		return;

	ucr4 = imx_uart_readl(sport, UCR4);
	ucr4 &= ~UCR4_TCEN;
	imx_uart_writel(sport, ucr4, UCR4);

	sport->tx_bytes = uart_circ_chars_pending(xmit);

	if (xmit->tail < xmit->head) {
		sport->dma_tx_nents = 1;
		sg_init_one(sgl, xmit->buf + xmit->tail, sport->tx_bytes);
	} else {
		sport->dma_tx_nents = 2;
		sg_init_table(sgl, 2);
		sg_set_buf(sgl, xmit->buf + xmit->tail,
				UART_XMIT_SIZE - xmit->tail);
		sg_set_buf(sgl + 1, xmit->buf, xmit->head);
	}

	ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
	if (ret == 0) {
		dev_err(dev, "DMA mapping error for TX.\n");
		return;
	}
	desc = dmaengine_prep_slave_sg(chan, sgl, sport->dma_tx_nents,
					DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT);
	if (!desc) {
		dma_unmap_sg(dev, sgl, sport->dma_tx_nents,
			     DMA_TO_DEVICE);
		dev_err(dev, "We cannot prepare for the TX slave dma!\n");
		return;
	}
	desc->callback = imx_uart_dma_tx_callback;
	desc->callback_param = sport;

	dev_dbg(dev, "TX: prepare to send %lu bytes by DMA.\n",
			uart_circ_chars_pending(xmit));

	ucr1 = imx_uart_readl(sport, UCR1);
	ucr1 |= UCR1_TXDMAEN;
	imx_uart_writel(sport, ucr1, UCR1);

	/* fire it */
	sport->dma_is_txing = 1;
	dmaengine_submit(desc);
	dma_async_issue_pending(chan);
	return;
}

/* called with port.lock taken and irqs off */
static void imx_uart_start_tx(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	u32 ucr1;

	if (!sport->port.x_char && uart_circ_empty(&port->state->xmit))
		return;

	if (port->rs485.flags & SER_RS485_ENABLED) {
		u32 ucr2;

		ucr2 = imx_uart_readl(sport, UCR2);
		if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
			imx_uart_rts_active(sport, &ucr2);
		else
			imx_uart_rts_inactive(sport, &ucr2);
		imx_uart_writel(sport, ucr2, UCR2);

		if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
			imx_uart_stop_rx(port);

		/*
		 * Enable transmitter and shifter empty irq only if DMA is off.
		 * In the DMA case this is done in the tx-callback.
		 */
		if (!sport->dma_is_enabled) {
			u32 ucr4 = imx_uart_readl(sport, UCR4);
			ucr4 |= UCR4_TCEN;
			imx_uart_writel(sport, ucr4, UCR4);
		}
	}

	if (!sport->dma_is_enabled) {
		ucr1 = imx_uart_readl(sport, UCR1);
		imx_uart_writel(sport, ucr1 | UCR1_TXMPTYEN, UCR1);
	}

	if (sport->dma_is_enabled) {
		if (sport->port.x_char) {
			/* We have X-char to send, so enable TX IRQ and
			 * disable TX DMA to let TX interrupt to send X-char */
			ucr1 = imx_uart_readl(sport, UCR1);
			ucr1 &= ~UCR1_TXDMAEN;
			ucr1 |= UCR1_TXMPTYEN;
			imx_uart_writel(sport, ucr1, UCR1);
			return;
		}

		if (!uart_circ_empty(&port->state->xmit) &&
		    !uart_tx_stopped(port))
			imx_uart_dma_tx(sport);
		return;
	}
}

static irqreturn_t imx_uart_rtsint(int irq, void *dev_id)
{
	struct imx_port *sport = dev_id;
	u32 usr1;

	spin_lock(&sport->port.lock);

	imx_uart_writel(sport, USR1_RTSD, USR1);
	usr1 = imx_uart_readl(sport, USR1) & USR1_RTSS;
	uart_handle_cts_change(&sport->port, !!usr1);
	wake_up_interruptible(&sport->port.state->port.delta_msr_wait);

	spin_unlock(&sport->port.lock);
	return IRQ_HANDLED;
}

static irqreturn_t imx_uart_txint(int irq, void *dev_id)
{
	struct imx_port *sport = dev_id;

	spin_lock(&sport->port.lock);
	imx_uart_transmit_buffer(sport);
	spin_unlock(&sport->port.lock);
	return IRQ_HANDLED;
}

static irqreturn_t imx_uart_rxint(int irq, void *dev_id)
{
	struct imx_port *sport = dev_id;
	unsigned int rx, flg, ignored = 0;
	struct tty_port *port = &sport->port.state->port;

	spin_lock(&sport->port.lock);

	while (imx_uart_readl(sport, USR2) & USR2_RDR) {
		u32 usr2;

		flg = TTY_NORMAL;
		sport->port.icount.rx++;

		rx = imx_uart_readl(sport, URXD0);

		usr2 = imx_uart_readl(sport, USR2);
		if (usr2 & USR2_BRCD) {
			imx_uart_writel(sport, USR2_BRCD, USR2);
			if (uart_handle_break(&sport->port))
				continue;
		}

		if (uart_handle_sysrq_char(&sport->port, (unsigned char)rx))
			continue;

		if (unlikely(rx & URXD_ERR)) {
			if (rx & URXD_BRK)
				sport->port.icount.brk++;
			else if (rx & URXD_PRERR)
				sport->port.icount.parity++;
			else if (rx & URXD_FRMERR)
				sport->port.icount.frame++;
			if (rx & URXD_OVRRUN)
				sport->port.icount.overrun++;

			if (rx & sport->port.ignore_status_mask) {
				if (++ignored > 100)
					goto out;
				continue;
			}

			rx &= (sport->port.read_status_mask | 0xFF);

			if (rx & URXD_BRK)
				flg = TTY_BREAK;
			else if (rx & URXD_PRERR)
				flg = TTY_PARITY;
			else if (rx & URXD_FRMERR)
				flg = TTY_FRAME;
			if (rx & URXD_OVRRUN)
				flg = TTY_OVERRUN;

#ifdef SUPPORT_SYSRQ
			sport->port.sysrq = 0;
#endif
		}

		if (sport->port.ignore_status_mask & URXD_DUMMY_READ)
			goto out;

		if (tty_insert_flip_char(port, rx, flg) == 0)
			sport->port.icount.buf_overrun++;
	}

out:
	spin_unlock(&sport->port.lock);
	tty_flip_buffer_push(port);
	return IRQ_HANDLED;
}

static void imx_uart_clear_rx_errors(struct imx_port *sport);

/*
 * We have a modem side uart, so the meanings of RTS and CTS are inverted.
 */
static unsigned int imx_uart_get_hwmctrl(struct imx_port *sport)
{
	unsigned int tmp = TIOCM_DSR;
	unsigned usr1 = imx_uart_readl(sport, USR1);
	unsigned usr2 = imx_uart_readl(sport, USR2);

	if (usr1 & USR1_RTSS)
		tmp |= TIOCM_CTS;

	/* in DCE mode DCDIN is always 0 */
	if (!(usr2 & USR2_DCDIN))
		tmp |= TIOCM_CAR;

	if (sport->dte_mode)
		if (!(imx_uart_readl(sport, USR2) & USR2_RIIN))
			tmp |= TIOCM_RI;

	return tmp;
}

/*
 * Handle any change of modem status signal since we were last called.
 */
static void imx_uart_mctrl_check(struct imx_port *sport)
{
	unsigned int status, changed;

	status = imx_uart_get_hwmctrl(sport);
	changed = status ^ sport->old_status;

	if (changed == 0)
		return;

	sport->old_status = status;

	if (changed & TIOCM_RI && status & TIOCM_RI)
		sport->port.icount.rng++;
	if (changed & TIOCM_DSR)
		sport->port.icount.dsr++;
	if (changed & TIOCM_CAR)
		uart_handle_dcd_change(&sport->port, status & TIOCM_CAR);
	if (changed & TIOCM_CTS)
		uart_handle_cts_change(&sport->port, status & TIOCM_CTS);

	wake_up_interruptible(&sport->port.state->port.delta_msr_wait);
}

static irqreturn_t imx_uart_int(int irq, void *dev_id)
{
	struct imx_port *sport = dev_id;
	unsigned int usr1, usr2, ucr1, ucr2, ucr3, ucr4;
	irqreturn_t ret = IRQ_NONE;

	usr1 = imx_uart_readl(sport, USR1);
	usr2 = imx_uart_readl(sport, USR2);
	ucr1 = imx_uart_readl(sport, UCR1);
	ucr2 = imx_uart_readl(sport, UCR2);
	ucr3 = imx_uart_readl(sport, UCR3);
	ucr4 = imx_uart_readl(sport, UCR4);

	/*
	 * Even if a condition is true that can trigger an irq only handle it if
	 * the respective irq source is enabled. This prevents some undesired
	 * actions, for example if a character that sits in the RX FIFO and that
	 * should be fetched via DMA is tried to be fetched using PIO. Or the
	 * receiver is currently off and so reading from URXD0 results in an
	 * exception. So just mask the (raw) status bits for disabled irqs.
	 */
	if ((ucr1 & UCR1_RRDYEN) == 0)
		usr1 &= ~USR1_RRDY;
	if ((ucr2 & UCR2_ATEN) == 0)
		usr1 &= ~USR1_AGTIM;
	if ((ucr1 & UCR1_TXMPTYEN) == 0)
		usr1 &= ~USR1_TRDY;
	if ((ucr4 & UCR4_TCEN) == 0)
		usr2 &= ~USR2_TXDC;
	if ((ucr3 & UCR3_DTRDEN) == 0)
		usr1 &= ~USR1_DTRD;
	if ((ucr1 & UCR1_RTSDEN) == 0)
		usr1 &= ~USR1_RTSD;
	if ((ucr3 & UCR3_AWAKEN) == 0)
		usr1 &= ~USR1_AWAKE;
	if ((ucr4 & UCR4_OREN) == 0)
		usr2 &= ~USR2_ORE;

	if (usr1 & (USR1_RRDY | USR1_AGTIM)) {
		imx_uart_rxint(irq, dev_id);
		ret = IRQ_HANDLED;
	}

	if ((usr1 & USR1_TRDY) || (usr2 & USR2_TXDC)) {
		imx_uart_txint(irq, dev_id);
		ret = IRQ_HANDLED;
	}

	if (usr1 & USR1_DTRD) {
		imx_uart_writel(sport, USR1_DTRD, USR1);

		spin_lock(&sport->port.lock);
		imx_uart_mctrl_check(sport);
		spin_unlock(&sport->port.lock);

		ret = IRQ_HANDLED;
	}

	if (usr1 & USR1_RTSD) {
		imx_uart_rtsint(irq, dev_id);
		ret = IRQ_HANDLED;
	}

	if (usr1 & USR1_AWAKE) {
		imx_uart_writel(sport, USR1_AWAKE, USR1);
		ret = IRQ_HANDLED;
	}

	if (usr2 & USR2_ORE) {
		sport->port.icount.overrun++;
		imx_uart_writel(sport, USR2_ORE, USR2);
		ret = IRQ_HANDLED;
	}

	return ret;
}

/*
 * Return TIOCSER_TEMT when transmitter is not busy.
 */
static unsigned int imx_uart_tx_empty(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	unsigned int ret;

	ret = (imx_uart_readl(sport, USR2) & USR2_TXDC) ?  TIOCSER_TEMT : 0;

	/* If the TX DMA is working, return 0. */
	if (sport->dma_is_txing)
		ret = 0;

	return ret;
}

/* called with port.lock taken and irqs off */
static unsigned int imx_uart_get_mctrl(struct uart_port *port)
{
	struct imx_port *sport = (struct imx_port *)port;
	unsigned int ret = imx_uart_get_hwmctrl(sport);

	mctrl_gpio_get(sport->gpios, &ret);

	return ret;
}

/* called with port.lock taken and irqs off */
static void imx_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
	struct imx_port *sport = (struct imx_port *)port;
	u32 ucr3, uts;

	if (!(port->rs485.flags & SER_RS485_ENABLED)) {
		u32 ucr2;

		ucr2 = imx_uart_readl(sport, UCR2);
		ucr2 &= ~(UCR2_CTS | UCR2_CTSC);
		if (mctrl & TIOCM_RTS)
			ucr2 |= UCR2_CTS | UCR2_CTSC;
		imx_uart_writel(sport, ucr2, UCR2);
	}

	ucr3 = imx_uart_readl(sport, UCR3) & ~UCR3_DSR;
	if (!(mctrl & TIOCM_DTR))
		ucr3 |= UCR3_DSR;
	imx_uart_writel(sport, ucr3, UCR3);

	uts = imx_uart_readl(sport, imx_uart_uts_reg(sport)) & ~UTS_LOOP;
	if (mctrl & TIOCM_LOOP)
		uts |= UTS_LOOP;
	imx_uart_writel(sport, uts, imx_uart_uts_reg(sport));

	mctrl_gpio_set(sport->gpios, mctrl);
}

/*
 * Interrupts always disabled.
 */
static void imx_uart_break_ctl(struct uart_port *port, int break_state)
{
	struct imx_port *sport = (struct imx_port *)port;
	unsigned long flags;
	u32 ucr1;

	spin_lock_irqsave(&sport->port.lock, flags);

	ucr1 = imx_uart_readl(sport, UCR1) & ~UCR1_SNDBRK;