drivers/tty/serial/stm32-usart.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) Maxime Coquelin 2015
 * Copyright (C) STMicroelectronics SA 2017
 * Authors:  Maxime Coquelin <mcoquelin.stm32@gmail.com>
 *	     Gerald Baeza <gerald.baeza@foss.st.com>
 *	     Erwan Le Ray <erwan.leray@foss.st.com>
 *
 * Inspired by st-asc.c from STMicroelectronics (c)
 */

#include <linux/clk.h>
#include <linux/console.h>
#include <linux/delay.h>
#include <linux/dma-direction.h>
#include <linux/dmaengine.h>
#include <linux/dma-mapping.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/irq.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_platform.h>
#include <linux/pinctrl/consumer.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/pm_wakeirq.h>
#include <linux/serial_core.h>
#include <linux/serial.h>
#include <linux/spinlock.h>
#include <linux/sysrq.h>
#include <linux/tty_flip.h>
#include <linux/tty.h>

#include "serial_mctrl_gpio.h"
#include "stm32-usart.h"

static void stm32_usart_stop_tx(struct uart_port *port);
static void stm32_usart_transmit_chars(struct uart_port *port);

static inline struct stm32_port *to_stm32_port(struct uart_port *port)
{
	return container_of(port, struct stm32_port, port);
}

static void stm32_usart_set_bits(struct uart_port *port, u32 reg, u32 bits)
{
	u32 val;

	val = readl_relaxed(port->membase + reg);
	val |= bits;
	writel_relaxed(val, port->membase + reg);
}

static void stm32_usart_clr_bits(struct uart_port *port, u32 reg, u32 bits)
{
	u32 val;

	val = readl_relaxed(port->membase + reg);
	val &= ~bits;
	writel_relaxed(val, port->membase + reg);
}

static void stm32_usart_config_reg_rs485(u32 *cr1, u32 *cr3, u32 delay_ADE,
					 u32 delay_DDE, u32 baud)
{
	u32 rs485_deat_dedt;
	u32 rs485_deat_dedt_max = (USART_CR1_DEAT_MASK >> USART_CR1_DEAT_SHIFT);
	bool over8;

	*cr3 |= USART_CR3_DEM;
	over8 = *cr1 & USART_CR1_OVER8;

	if (over8)
		rs485_deat_dedt = delay_ADE * baud * 8;
	else
		rs485_deat_dedt = delay_ADE * baud * 16;

	rs485_deat_dedt = DIV_ROUND_CLOSEST(rs485_deat_dedt, 1000);
	rs485_deat_dedt = rs485_deat_dedt > rs485_deat_dedt_max ?
			  rs485_deat_dedt_max : rs485_deat_dedt;
	rs485_deat_dedt = (rs485_deat_dedt << USART_CR1_DEAT_SHIFT) &
			   USART_CR1_DEAT_MASK;
	*cr1 |= rs485_deat_dedt;

	if (over8)
		rs485_deat_dedt = delay_DDE * baud * 8;
	else
		rs485_deat_dedt = delay_DDE * baud * 16;

	rs485_deat_dedt = DIV_ROUND_CLOSEST(rs485_deat_dedt, 1000);
	rs485_deat_dedt = rs485_deat_dedt > rs485_deat_dedt_max ?
			  rs485_deat_dedt_max : rs485_deat_dedt;
	rs485_deat_dedt = (rs485_deat_dedt << USART_CR1_DEDT_SHIFT) &
			   USART_CR1_DEDT_MASK;
	*cr1 |= rs485_deat_dedt;
}

static int stm32_usart_config_rs485(struct uart_port *port,
				    struct serial_rs485 *rs485conf)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
	u32 usartdiv, baud, cr1, cr3;
	bool over8;

	stm32_usart_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));

	port->rs485 = *rs485conf;

	rs485conf->flags |= SER_RS485_RX_DURING_TX;

	if (rs485conf->flags & SER_RS485_ENABLED) {
		cr1 = readl_relaxed(port->membase + ofs->cr1);
		cr3 = readl_relaxed(port->membase + ofs->cr3);
		usartdiv = readl_relaxed(port->membase + ofs->brr);
		usartdiv = usartdiv & GENMASK(15, 0);
		over8 = cr1 & USART_CR1_OVER8;

		if (over8)
			usartdiv = usartdiv | (usartdiv & GENMASK(4, 0))
				   << USART_BRR_04_R_SHIFT;

		baud = DIV_ROUND_CLOSEST(port->uartclk, usartdiv);
		stm32_usart_config_reg_rs485(&cr1, &cr3,
					     rs485conf->delay_rts_before_send,
					     rs485conf->delay_rts_after_send,
					     baud);

		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
			cr3 &= ~USART_CR3_DEP;
			rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
		} else {
			cr3 |= USART_CR3_DEP;
			rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
		}

		writel_relaxed(cr3, port->membase + ofs->cr3);
		writel_relaxed(cr1, port->membase + ofs->cr1);
	} else {
		stm32_usart_clr_bits(port, ofs->cr3,
				     USART_CR3_DEM | USART_CR3_DEP);
		stm32_usart_clr_bits(port, ofs->cr1,
				     USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
	}

	stm32_usart_set_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));

	return 0;
}

static int stm32_usart_init_rs485(struct uart_port *port,
				  struct platform_device *pdev)
{
	struct serial_rs485 *rs485conf = &port->rs485;

	rs485conf->flags = 0;
	rs485conf->delay_rts_before_send = 0;
	rs485conf->delay_rts_after_send = 0;

	if (!pdev->dev.of_node)
		return -ENODEV;

	return uart_get_rs485_mode(port);
}

static bool stm32_usart_rx_dma_enabled(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if (!stm32_port->rx_ch)
		return false;

	return !!(readl_relaxed(port->membase + ofs->cr3) & USART_CR3_DMAR);
}

/* Return true when data is pending (in pio mode), and false when no data is pending. */
static bool stm32_usart_pending_rx_pio(struct uart_port *port, u32 *sr)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	*sr = readl_relaxed(port->membase + ofs->isr);
	/* Get pending characters in RDR or FIFO */
	if (*sr & USART_SR_RXNE) {
		/* Get all pending characters from the RDR or the FIFO when using interrupts */
		if (!stm32_usart_rx_dma_enabled(port))
			return true;

		/* Handle only RX data errors when using DMA */
		if (*sr & USART_SR_ERR_MASK)
			return true;
	}

	return false;
}

static unsigned long stm32_usart_get_char_pio(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	unsigned long c;

	c = readl_relaxed(port->membase + ofs->rdr);
	/* Apply RDR data mask */
	c &= stm32_port->rdr_mask;

	return c;
}

static void stm32_usart_receive_chars_pio(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	unsigned long c;
	u32 sr;
	char flag;

	while (stm32_usart_pending_rx_pio(port, &sr)) {
		sr |= USART_SR_DUMMY_RX;
		flag = TTY_NORMAL;

		/*
		 * Status bits has to be cleared before reading the RDR:
		 * In FIFO mode, reading the RDR will pop the next data
		 * (if any) along with its status bits into the SR.
		 * Not doing so leads to misalignement between RDR and SR,
		 * and clear status bits of the next rx data.
		 *
		 * Clear errors flags for stm32f7 and stm32h7 compatible
		 * devices. On stm32f4 compatible devices, the error bit is
		 * cleared by the sequence [read SR - read DR].
		 */
		if ((sr & USART_SR_ERR_MASK) && ofs->icr != UNDEF_REG)
			writel_relaxed(sr & USART_SR_ERR_MASK,
				       port->membase + ofs->icr);

		c = stm32_usart_get_char_pio(port);
		port->icount.rx++;
		if (sr & USART_SR_ERR_MASK) {
			if (sr & USART_SR_ORE) {
				port->icount.overrun++;
			} else if (sr & USART_SR_PE) {
				port->icount.parity++;
			} else if (sr & USART_SR_FE) {
				/* Break detection if character is null */
				if (!c) {
					port->icount.brk++;
					if (uart_handle_break(port))
						continue;
				} else {
					port->icount.frame++;
				}
			}

			sr &= port->read_status_mask;

			if (sr & USART_SR_PE) {
				flag = TTY_PARITY;
			} else if (sr & USART_SR_FE) {
				if (!c)
					flag = TTY_BREAK;
				else
					flag = TTY_FRAME;
			}
		}

		if (uart_prepare_sysrq_char(port, c))
			continue;
		uart_insert_char(port, sr, USART_SR_ORE, c, flag);
	}
}

static void stm32_usart_push_buffer_dma(struct uart_port *port, unsigned int dma_size)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	struct tty_port *ttyport = &stm32_port->port.state->port;
	unsigned char *dma_start;
	int dma_count, i;

	dma_start = stm32_port->rx_buf + (RX_BUF_L - stm32_port->last_res);

	/*
	 * Apply rdr_mask on buffer in order to mask parity bit.
	 * This loop is useless in cs8 mode because DMA copies only
	 * 8 bits and already ignores parity bit.
	 */
	if (!(stm32_port->rdr_mask == (BIT(8) - 1)))
		for (i = 0; i < dma_size; i++)
			*(dma_start + i) &= stm32_port->rdr_mask;

	dma_count = tty_insert_flip_string(ttyport, dma_start, dma_size);
	port->icount.rx += dma_count;
	if (dma_count != dma_size)
		port->icount.buf_overrun++;
	stm32_port->last_res -= dma_count;
	if (stm32_port->last_res == 0)
		stm32_port->last_res = RX_BUF_L;
}

static void stm32_usart_receive_chars_dma(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	unsigned int dma_size;

	/* DMA buffer is configured in cyclic mode and handles the rollback of the buffer. */
	if (stm32_port->rx_dma_state.residue > stm32_port->last_res) {
		/* Conditional first part: from last_res to end of DMA buffer */
		dma_size = stm32_port->last_res;
		stm32_usart_push_buffer_dma(port, dma_size);
	}

	dma_size = stm32_port->last_res - stm32_port->rx_dma_state.residue;
	stm32_usart_push_buffer_dma(port, dma_size);
}

static void stm32_usart_receive_chars(struct uart_port *port, bool irqflag)
{
	struct tty_port *tport = &port->state->port;
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	enum dma_status rx_dma_status;
	unsigned long flags;
	u32 sr;

	if (irqflag)
		spin_lock_irqsave(&port->lock, flags);
	else
		spin_lock(&port->lock);

	if (stm32_usart_rx_dma_enabled(port)) {
		rx_dma_status = dmaengine_tx_status(stm32_port->rx_ch,
						    stm32_port->rx_ch->cookie,
						    &stm32_port->rx_dma_state);
		if (rx_dma_status == DMA_IN_PROGRESS) {
			/* Empty DMA buffer */
			stm32_usart_receive_chars_dma(port);
			sr = readl_relaxed(port->membase + ofs->isr);
			if (sr & USART_SR_ERR_MASK) {
				/* Disable DMA request line */
				stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAR);

				/* Switch to PIO mode to handle the errors */
				stm32_usart_receive_chars_pio(port);

				/* Switch back to DMA mode */
				stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAR);
			}
		} else {
			/* Disable RX DMA */
			dmaengine_terminate_async(stm32_port->rx_ch);
			stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAR);
			/* Fall back to interrupt mode */
			dev_dbg(port->dev, "DMA error, fallback to irq mode\n");
			stm32_usart_receive_chars_pio(port);
		}
	} else {
		stm32_usart_receive_chars_pio(port);
	}

	if (irqflag)
		uart_unlock_and_check_sysrq_irqrestore(port, irqflag);
	else
		uart_unlock_and_check_sysrq(port);

	tty_flip_buffer_push(tport);
}

static void stm32_usart_tx_dma_complete(void *arg)
{
	struct uart_port *port = arg;
	struct stm32_port *stm32port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
	unsigned long flags;

	dmaengine_terminate_async(stm32port->tx_ch);
	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
	stm32port->tx_dma_busy = false;

	/* Let's see if we have pending data to send */
	spin_lock_irqsave(&port->lock, flags);
	stm32_usart_transmit_chars(port);
	spin_unlock_irqrestore(&port->lock, flags);
}

static void stm32_usart_tx_interrupt_enable(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	/*
	 * Enables TX FIFO threashold irq when FIFO is enabled,
	 * or TX empty irq when FIFO is disabled
	 */
	if (stm32_port->fifoen && stm32_port->txftcfg >= 0)
		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_TXFTIE);
	else
		stm32_usart_set_bits(port, ofs->cr1, USART_CR1_TXEIE);
}

static void stm32_usart_rx_dma_complete(void *arg)
{
	struct uart_port *port = arg;

	stm32_usart_receive_chars(port, true);
}

static void stm32_usart_tx_interrupt_disable(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if (stm32_port->fifoen && stm32_port->txftcfg >= 0)
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_TXFTIE);
	else
		stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_TXEIE);
}

static void stm32_usart_transmit_chars_pio(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	struct circ_buf *xmit = &port->state->xmit;

	if (stm32_port->tx_dma_busy) {
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
		stm32_port->tx_dma_busy = false;
	}

	while (!uart_circ_empty(xmit)) {
		/* Check that TDR is empty before filling FIFO */
		if (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
			break;
		writel_relaxed(xmit->buf[xmit->tail], port->membase + ofs->tdr);
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		port->icount.tx++;
	}

	/* rely on TXE irq (mask or unmask) for sending remaining data */
	if (uart_circ_empty(xmit))
		stm32_usart_tx_interrupt_disable(port);
	else
		stm32_usart_tx_interrupt_enable(port);
}

static void stm32_usart_transmit_chars_dma(struct uart_port *port)
{
	struct stm32_port *stm32port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
	struct circ_buf *xmit = &port->state->xmit;
	struct dma_async_tx_descriptor *desc = NULL;
	unsigned int count, i;

	if (stm32port->tx_dma_busy)
		return;

	stm32port->tx_dma_busy = true;

	count = uart_circ_chars_pending(xmit);

	if (count > TX_BUF_L)
		count = TX_BUF_L;

	if (xmit->tail < xmit->head) {
		memcpy(&stm32port->tx_buf[0], &xmit->buf[xmit->tail], count);
	} else {
		size_t one = UART_XMIT_SIZE - xmit->tail;
		size_t two;

		if (one > count)
			one = count;
		two = count - one;

		memcpy(&stm32port->tx_buf[0], &xmit->buf[xmit->tail], one);
		if (two)
			memcpy(&stm32port->tx_buf[one], &xmit->buf[0], two);
	}

	desc = dmaengine_prep_slave_single(stm32port->tx_ch,
					   stm32port->tx_dma_buf,
					   count,
					   DMA_MEM_TO_DEV,
					   DMA_PREP_INTERRUPT);

	if (!desc)
		goto fallback_err;

	desc->callback = stm32_usart_tx_dma_complete;
	desc->callback_param = port;

	/* Push current DMA TX transaction in the pending queue */
	if (dma_submit_error(dmaengine_submit(desc))) {
		/* dma no yet started, safe to free resources */
		dmaengine_terminate_async(stm32port->tx_ch);
		goto fallback_err;
	}

	/* Issue pending DMA TX requests */
	dma_async_issue_pending(stm32port->tx_ch);

	stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);

	xmit->tail = (xmit->tail + count) & (UART_XMIT_SIZE - 1);
	port->icount.tx += count;
	return;

fallback_err:
	for (i = count; i > 0; i--)
		stm32_usart_transmit_chars_pio(port);
}

static void stm32_usart_transmit_chars(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	struct circ_buf *xmit = &port->state->xmit;

	if (port->x_char) {
		if (stm32_port->tx_dma_busy)
			stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
		writel_relaxed(port->x_char, port->membase + ofs->tdr);
		port->x_char = 0;
		port->icount.tx++;
		if (stm32_port->tx_dma_busy)
			stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);
		return;
	}

	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
		stm32_usart_tx_interrupt_disable(port);
		return;
	}

	if (ofs->icr == UNDEF_REG)
		stm32_usart_clr_bits(port, ofs->isr, USART_SR_TC);
	else
		writel_relaxed(USART_ICR_TCCF, port->membase + ofs->icr);

	if (stm32_port->tx_ch)
		stm32_usart_transmit_chars_dma(port);
	else
		stm32_usart_transmit_chars_pio(port);

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

	if (uart_circ_empty(xmit))
		stm32_usart_tx_interrupt_disable(port);
}

static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
{
	struct uart_port *port = ptr;
	struct tty_port *tport = &port->state->port;
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	u32 sr;

	sr = readl_relaxed(port->membase + ofs->isr);

	if ((sr & USART_SR_RTOF) && ofs->icr != UNDEF_REG)
		writel_relaxed(USART_ICR_RTOCF,
			       port->membase + ofs->icr);

	if ((sr & USART_SR_WUF) && ofs->icr != UNDEF_REG) {
		/* Clear wake up flag and disable wake up interrupt */
		writel_relaxed(USART_ICR_WUCF,
			       port->membase + ofs->icr);
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_WUFIE);
		if (irqd_is_wakeup_set(irq_get_irq_data(port->irq)))
			pm_wakeup_event(tport->tty->dev, 0);
	}

	/*
	 * rx errors in dma mode has to be handled ASAP to avoid overrun as the DMA request
	 * line has been masked by HW and rx data are stacking in FIFO.
	 */
	if (!stm32_port->throttled) {
		if (((sr & USART_SR_RXNE) && !stm32_usart_rx_dma_enabled(port)) ||
		    ((sr & USART_SR_ERR_MASK) && stm32_usart_rx_dma_enabled(port))) {
			stm32_usart_receive_chars(port, false);
		}
	}

	if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) {
		spin_lock(&port->lock);
		stm32_usart_transmit_chars(port);
		spin_unlock(&port->lock);
	}

	if (stm32_usart_rx_dma_enabled(port))
		return IRQ_WAKE_THREAD;
	else
		return IRQ_HANDLED;
}

static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
{
	struct uart_port *port = ptr;
	struct stm32_port *stm32_port = to_stm32_port(port);

	/* Receiver timeout irq for DMA RX */
	if (!stm32_port->throttled)
		stm32_usart_receive_chars(port, false);

	return IRQ_HANDLED;
}

static unsigned int stm32_usart_tx_empty(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if (readl_relaxed(port->membase + ofs->isr) & USART_SR_TC)
		return TIOCSER_TEMT;

	return 0;
}

static void stm32_usart_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if ((mctrl & TIOCM_RTS) && (port->status & UPSTAT_AUTORTS))
		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_RTSE);
	else
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_RTSE);

	mctrl_gpio_set(stm32_port->gpios, mctrl);
}

static unsigned int stm32_usart_get_mctrl(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	unsigned int ret;

	/* This routine is used to get signals of: DCD, DSR, RI, and CTS */
	ret = TIOCM_CAR | TIOCM_DSR | TIOCM_CTS;

	return mctrl_gpio_get(stm32_port->gpios, &ret);
}

static void stm32_usart_enable_ms(struct uart_port *port)
{
	mctrl_gpio_enable_ms(to_stm32_port(port)->gpios);
}

static void stm32_usart_disable_ms(struct uart_port *port)
{
	mctrl_gpio_disable_ms(to_stm32_port(port)->gpios);
}

/* Transmit stop */
static void stm32_usart_stop_tx(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	struct serial_rs485 *rs485conf = &port->rs485;

	stm32_usart_tx_interrupt_disable(port);

	if (rs485conf->flags & SER_RS485_ENABLED) {
		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
			mctrl_gpio_set(stm32_port->gpios,
					stm32_port->port.mctrl & ~TIOCM_RTS);
		} else {
			mctrl_gpio_set(stm32_port->gpios,
					stm32_port->port.mctrl | TIOCM_RTS);
		}
	}
}

/* There are probably characters waiting to be transmitted. */
static void stm32_usart_start_tx(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	struct serial_rs485 *rs485conf = &port->rs485;
	struct circ_buf *xmit = &port->state->xmit;

	if (uart_circ_empty(xmit))
		return;

	if (rs485conf->flags & SER_RS485_ENABLED) {
		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
			mctrl_gpio_set(stm32_port->gpios,
					stm32_port->port.mctrl | TIOCM_RTS);
		} else {
			mctrl_gpio_set(stm32_port->gpios,
					stm32_port->port.mctrl & ~TIOCM_RTS);
		}
	}

	stm32_usart_transmit_chars(port);
}

/* Flush the transmit buffer. */
static void stm32_usart_flush_buffer(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if (stm32_port->tx_ch) {
		dmaengine_terminate_async(stm32_port->tx_ch);
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
		stm32_port->tx_dma_busy = false;
	}
}

/* Throttle the remote when input buffer is about to overflow. */
static void stm32_usart_throttle(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);

	/*
	 * Disable DMA request line if enabled, so the RX data gets queued into the FIFO.
	 * Hardware flow control is triggered when RX FIFO is full.
	 */
	if (stm32_usart_rx_dma_enabled(port))
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAR);

	stm32_usart_clr_bits(port, ofs->cr1, stm32_port->cr1_irq);
	if (stm32_port->cr3_irq)
		stm32_usart_clr_bits(port, ofs->cr3, stm32_port->cr3_irq);

	stm32_port->throttled = true;
	spin_unlock_irqrestore(&port->lock, flags);
}

/* Unthrottle the remote, the input buffer can now accept data. */
static void stm32_usart_unthrottle(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	unsigned long flags;

	spin_lock_irqsave(&port->lock, flags);
	stm32_usart_set_bits(port, ofs->cr1, stm32_port->cr1_irq);
	if (stm32_port->cr3_irq)
		stm32_usart_set_bits(port, ofs->cr3, stm32_port->cr3_irq);

	/*
	 * Switch back to DMA mode (re-enable DMA request line).
	 * Hardware flow control is stopped when FIFO is not full any more.
	 */
	if (stm32_port->rx_ch)
		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAR);

	stm32_port->throttled = false;
	spin_unlock_irqrestore(&port->lock, flags);
}

/* Receive stop */
static void stm32_usart_stop_rx(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	stm32_usart_clr_bits(port, ofs->cr1, stm32_port->cr1_irq);
	if (stm32_port->cr3_irq)
		stm32_usart_clr_bits(port, ofs->cr3, stm32_port->cr3_irq);
}

/* Handle breaks - ignored by us */
static void stm32_usart_break_ctl(struct uart_port *port, int break_state)
{
}

static int stm32_usart_startup(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
	const char *name = to_platform_device(port->dev)->name;
	u32 val;
	int ret;

	ret = request_threaded_irq(port->irq, stm32_usart_interrupt,
				   stm32_usart_threaded_interrupt,
				   IRQF_ONESHOT | IRQF_NO_SUSPEND,
				   name, port);
	if (ret)
		return ret;

	if (stm32_port->swap) {
		val = readl_relaxed(port->membase + ofs->cr2);
		val |= USART_CR2_SWAP;
		writel_relaxed(val, port->membase + ofs->cr2);
	}

	/* RX FIFO Flush */
	if (ofs->rqr != UNDEF_REG)
		writel_relaxed(USART_RQR_RXFRQ, port->membase + ofs->rqr);

	/*
	 * DMA request line not re-enabled at resume when port is throttled.
	 * It will be re-enabled by unthrottle ops.
	 */
	if (!stm32_port->throttled)
		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAR);

	/* RX enabling */
	val = stm32_port->cr1_irq | USART_CR1_RE | BIT(cfg->uart_enable_bit);
	stm32_usart_set_bits(port, ofs->cr1, val);

	return 0;
}

static void stm32_usart_shutdown(struct uart_port *port)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
	u32 val, isr;
	int ret;

	/* Disable modem control interrupts */
	stm32_usart_disable_ms(port);

	val = USART_CR1_TXEIE | USART_CR1_TE;
	val |= stm32_port->cr1_irq | USART_CR1_RE;
	val |= BIT(cfg->uart_enable_bit);
	if (stm32_port->fifoen)
		val |= USART_CR1_FIFOEN;

	ret = readl_relaxed_poll_timeout(port->membase + ofs->isr,
					 isr, (isr & USART_SR_TC),
					 10, 100000);

	/* Send the TC error message only when ISR_TC is not set */
	if (ret)
		dev_err(port->dev, "Transmission is not complete\n");

	/* flush RX & TX FIFO */
	if (ofs->rqr != UNDEF_REG)
		writel_relaxed(USART_RQR_TXFRQ | USART_RQR_RXFRQ,
			       port->membase + ofs->rqr);

	stm32_usart_clr_bits(port, ofs->cr1, val);

	free_irq(port->irq, port);
}

static void stm32_usart_set_termios(struct uart_port *port,
				    struct ktermios *termios,
				    struct ktermios *old)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
	struct serial_rs485 *rs485conf = &port->rs485;
	unsigned int baud, bits;
	u32 usartdiv, mantissa, fraction, oversampling;
	tcflag_t cflag = termios->c_cflag;
	u32 cr1, cr2, cr3, isr;
	unsigned long flags;
	int ret;

	if (!stm32_port->hw_flow_control)
		cflag &= ~CRTSCTS;

	baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 8);

	spin_lock_irqsave(&port->lock, flags);

	ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr,
						isr,
						(isr & USART_SR_TC),
						10, 100000);

	/* Send the TC error message only when ISR_TC is not set. */
	if (ret)
		dev_err(port->dev, "Transmission is not complete\n");

	/* Stop serial port and reset value */
	writel_relaxed(0, port->membase + ofs->cr1);

	/* flush RX & TX FIFO */
	if (ofs->rqr != UNDEF_REG)
		writel_relaxed(USART_RQR_TXFRQ | USART_RQR_RXFRQ,
			       port->membase + ofs->rqr);

	cr1 = USART_CR1_TE | USART_CR1_RE;
	if (stm32_port->fifoen)
		cr1 |= USART_CR1_FIFOEN;
	cr2 = stm32_port->swap ? USART_CR2_SWAP : 0;

	/* Tx and RX FIFO configuration */
	cr3 = readl_relaxed(port->membase + ofs->cr3);
	cr3 &= USART_CR3_TXFTIE | USART_CR3_RXFTIE;
	if (stm32_port->fifoen) {
		if (stm32_port->txftcfg >= 0)
			cr3 |= stm32_port->txftcfg << USART_CR3_TXFTCFG_SHIFT;
		if (stm32_port->rxftcfg >= 0)
			cr3 |= stm32_port->rxftcfg << USART_CR3_RXFTCFG_SHIFT;
	}

	if (cflag & CSTOPB)
		cr2 |= USART_CR2_STOP_2B;

	bits = tty_get_char_size(cflag);
	stm32_port->rdr_mask = (BIT(bits) - 1);

	if (cflag & PARENB) {
		bits++;
		cr1 |= USART_CR1_PCE;
	}

	/*
	 * Word length configuration:
	 * CS8 + parity, 9 bits word aka [M1:M0] = 0b01
	 * CS7 or (CS6 + parity), 7 bits word aka [M1:M0] = 0b10
	 * CS8 or (CS7 + parity), 8 bits word aka [M1:M0] = 0b00
	 * M0 and M1 already cleared by cr1 initialization.
	 */
	if (bits == 9)
		cr1 |= USART_CR1_M0;
	else if ((bits == 7) && cfg->has_7bits_data)
		cr1 |= USART_CR1_M1;
	else if (bits != 8)
		dev_dbg(port->dev, "Unsupported data bits config: %u bits\n"
			, bits);

	if (ofs->rtor != UNDEF_REG && (stm32_port->rx_ch ||
				       (stm32_port->fifoen &&
					stm32_port->rxftcfg >= 0))) {
		if (cflag & CSTOPB)
			bits = bits + 3; /* 1 start bit + 2 stop bits */
		else
			bits = bits + 2; /* 1 start bit + 1 stop bit */

		/* RX timeout irq to occur after last stop bit + bits */
		stm32_port->cr1_irq = USART_CR1_RTOIE;
		writel_relaxed(bits, port->membase + ofs->rtor);
		cr2 |= USART_CR2_RTOEN;
		/*
		 * Enable fifo threshold irq in two cases, either when there is no DMA, or when
		 * wake up over usart, from low power until the DMA gets re-enabled by resume.
		 */
		stm32_port->cr3_irq =  USART_CR3_RXFTIE;
	}

	cr1 |= stm32_port->cr1_irq;
	cr3 |= stm32_port->cr3_irq;

	if (cflag & PARODD)
		cr1 |= USART_CR1_PS;

	port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS);
	if (cflag & CRTSCTS) {
		port->status |= UPSTAT_AUTOCTS | UPSTAT_AUTORTS;
		cr3 |= USART_CR3_CTSE | USART_CR3_RTSE;
	}

	usartdiv = DIV_ROUND_CLOSEST(port->uartclk, baud);

	/*
	 * The USART supports 16 or 8 times oversampling.
	 * By default we prefer 16 times oversampling, so that the receiver
	 * has a better tolerance to clock deviations.
	 * 8 times oversampling is only used to achieve higher speeds.
	 */
	if (usartdiv < 16) {
		oversampling = 8;
		cr1 |= USART_CR1_OVER8;
		stm32_usart_set_bits(port, ofs->cr1, USART_CR1_OVER8);
	} else {
		oversampling = 16;
		cr1 &= ~USART_CR1_OVER8;
		stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_OVER8);
	}

	mantissa = (usartdiv / oversampling) << USART_BRR_DIV_M_SHIFT;
	fraction = usartdiv % oversampling;
	writel_relaxed(mantissa | fraction, port->membase + ofs->brr);

	uart_update_timeout(port, cflag, baud);

	port->read_status_mask = USART_SR_ORE;
	if (termios->c_iflag & INPCK)
		port->read_status_mask |= USART_SR_PE | USART_SR_FE;
	if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
		port->read_status_mask |= USART_SR_FE;

	/* Characters to ignore */
	port->ignore_status_mask = 0;
	if (termios->c_iflag & IGNPAR)
		port->ignore_status_mask = USART_SR_PE | USART_SR_FE;
	if (termios->c_iflag & IGNBRK) {
		port->ignore_status_mask |= USART_SR_FE;
		/*
		 * If we're ignoring parity and break indicators,
		 * ignore overruns too (for real raw support).
		 */
		if (termios->c_iflag & IGNPAR)
			port->ignore_status_mask |= USART_SR_ORE;
	}

	/* Ignore all characters if CREAD is not set */
	if ((termios->c_cflag & CREAD) == 0)
		port->ignore_status_mask |= USART_SR_DUMMY_RX;

	if (stm32_port->rx_ch) {
		/*
		 * Setup DMA to collect only valid data and enable error irqs.
		 * This also enables break reception when using DMA.
		 */
		cr1 |= USART_CR1_PEIE;
		cr3 |= USART_CR3_EIE;
		cr3 |= USART_CR3_DMAR;
		cr3 |= USART_CR3_DDRE;
	}

	if (rs485conf->flags & SER_RS485_ENABLED) {
		stm32_usart_config_reg_rs485(&cr1, &cr3,
					     rs485conf->delay_rts_before_send,
					     rs485conf->delay_rts_after_send,
					     baud);
		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
			cr3 &= ~USART_CR3_DEP;
			rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
		} else {
			cr3 |= USART_CR3_DEP;
			rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
		}

	} else {
		cr3 &= ~(USART_CR3_DEM | USART_CR3_DEP);
		cr1 &= ~(USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
	}

	/* Configure wake up from low power on start bit detection */
	if (stm32_port->wakeup_src) {
		cr3 &= ~USART_CR3_WUS_MASK;
		cr3 |= USART_CR3_WUS_START_BIT;
	}

	writel_relaxed(cr3, port->membase + ofs->cr3);
	writel_relaxed(cr2, port->membase + ofs->cr2);
	writel_relaxed(cr1, port->membase + ofs->cr1);

	stm32_usart_set_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
	spin_unlock_irqrestore(&port->lock, flags);

	/* Handle modem control interrupts */
	if (UART_ENABLE_MS(port, termios->c_cflag))
		stm32_usart_enable_ms(port);
	else
		stm32_usart_disable_ms(port);
}

static const char *stm32_usart_type(struct uart_port *port)
{
	return (port->type == PORT_STM32) ? DRIVER_NAME : NULL;
}

static void stm32_usart_release_port(struct uart_port *port)
{
}

static int stm32_usart_request_port(struct uart_port *port)
{
	return 0;
}

static void stm32_usart_config_port(struct uart_port *port, int flags)
{
	if (flags & UART_CONFIG_TYPE)
		port->type = PORT_STM32;
}

static int
stm32_usart_verify_port(struct uart_port *port, struct serial_struct *ser)
{
	/* No user changeable parameters */
	return -EINVAL;
}

static void stm32_usart_pm(struct uart_port *port, unsigned int state,
			   unsigned int oldstate)
{
	struct stm32_port *stm32port = container_of(port,
			struct stm32_port, port);
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32port->info->cfg;
	unsigned long flags;

	switch (state) {
	case UART_PM_STATE_ON:
		pm_runtime_get_sync(port->dev);
		break;
	case UART_PM_STATE_OFF:
		spin_lock_irqsave(&port->lock, flags);
		stm32_usart_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
		spin_unlock_irqrestore(&port->lock, flags);
		pm_runtime_put_sync(port->dev);
		break;
	}
}

static const struct uart_ops stm32_uart_ops = {
	.tx_empty	= stm32_usart_tx_empty,
	.set_mctrl	= stm32_usart_set_mctrl,
	.get_mctrl	= stm32_usart_get_mctrl,
	.stop_tx	= stm32_usart_stop_tx,
	.start_tx	= stm32_usart_start_tx,
	.throttle	= stm32_usart_throttle,
	.unthrottle	= stm32_usart_unthrottle,
	.stop_rx	= stm32_usart_stop_rx,
	.enable_ms	= stm32_usart_enable_ms,
	.break_ctl	= stm32_usart_break_ctl,
	.startup	= stm32_usart_startup,
	.shutdown	= stm32_usart_shutdown,
	.flush_buffer	= stm32_usart_flush_buffer,
	.set_termios	= stm32_usart_set_termios,
	.pm		= stm32_usart_pm,
	.type		= stm32_usart_type,
	.release_port	= stm32_usart_release_port,
	.request_port	= stm32_usart_request_port,
	.config_port	= stm32_usart_config_port,
	.verify_port	= stm32_usart_verify_port,
};

/*
 * STM32H7 RX & TX FIFO threshold configuration (CR3 RXFTCFG / TXFTCFG)
 * Note: 1 isn't a valid value in RXFTCFG / TXFTCFG. In this case,
 * RXNEIE / TXEIE can be used instead of threshold irqs: RXFTIE / TXFTIE.
 * So, RXFTCFG / TXFTCFG bitfields values are encoded as array index + 1.
 */
static const u32 stm32h7_usart_fifo_thresh_cfg[] = { 1, 2, 4, 8, 12, 14, 16 };

static void stm32_usart_get_ftcfg(struct platform_device *pdev, const char *p,
				  int *ftcfg)
{
	u32 bytes, i;

	/* DT option to get RX & TX FIFO threshold (default to 8 bytes) */
	if (of_property_read_u32(pdev->dev.of_node, p, &bytes))
		bytes = 8;

	for (i = 0; i < ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg); i++)
		if (stm32h7_usart_fifo_thresh_cfg[i] >= bytes)
			break;
	if (i >= ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg))
		i = ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg) - 1;

	dev_dbg(&pdev->dev, "%s set to %d bytes\n", p,
		stm32h7_usart_fifo_thresh_cfg[i]);

	/* Provide FIFO threshold ftcfg (1 is invalid: threshold irq unused) */
	if (i)
		*ftcfg = i - 1;
	else
		*ftcfg = -EINVAL;
}

static void stm32_usart_deinit_port(struct stm32_port *stm32port)
{
	clk_disable_unprepare(stm32port->clk);
}

static int stm32_usart_init_port(struct stm32_port *stm32port,
				 struct platform_device *pdev)
{
	struct uart_port *port = &stm32port->port;
	struct resource *res;
	int ret, irq;

	irq = platform_get_irq(pdev, 0);
	if (irq < 0)
		return irq;

	port->iotype	= UPIO_MEM;
	port->flags	= UPF_BOOT_AUTOCONF;
	port->ops	= &stm32_uart_ops;
	port->dev	= &pdev->dev;
	port->fifosize	= stm32port->info->cfg.fifosize;
	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_STM32_CONSOLE);
	port->irq = irq;
	port->rs485_config = stm32_usart_config_rs485;

	ret = stm32_usart_init_rs485(port, pdev);
	if (ret)
		return ret;

	stm32port->wakeup_src = stm32port->info->cfg.has_wakeup &&
		of_property_read_bool(pdev->dev.of_node, "wakeup-source");

	stm32port->swap = stm32port->info->cfg.has_swap &&
		of_property_read_bool(pdev->dev.of_node, "rx-tx-swap");

	stm32port->fifoen = stm32port->info->cfg.has_fifo;
	if (stm32port->fifoen) {
		stm32_usart_get_ftcfg(pdev, "rx-threshold",
				      &stm32port->rxftcfg);
		stm32_usart_get_ftcfg(pdev, "tx-threshold",
				      &stm32port->txftcfg);
	}

	port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
	if (IS_ERR(port->membase))
		return PTR_ERR(port->membase);
	port->mapbase = res->start;

	spin_lock_init(&port->lock);

	stm32port->clk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(stm32port->clk))
		return PTR_ERR(stm32port->clk);

	/* Ensure that clk rate is correct by enabling the clk */
	ret = clk_prepare_enable(stm32port->clk);
	if (ret)
		return ret;

	stm32port->port.uartclk = clk_get_rate(stm32port->clk);
	if (!stm32port->port.uartclk) {
		ret = -EINVAL;
		goto err_clk;
	}

	stm32port->gpios = mctrl_gpio_init(&stm32port->port, 0);
	if (IS_ERR(stm32port->gpios)) {
		ret = PTR_ERR(stm32port->gpios);
		goto err_clk;
	}

	/*
	 * Both CTS/RTS gpios and "st,hw-flow-ctrl" (deprecated) or "uart-has-rtscts"
	 * properties should not be specified.
	 */
	if (stm32port->hw_flow_control) {
		if (mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_CTS) ||
		    mctrl_gpio_to_gpiod(stm32port->gpios, UART_GPIO_RTS)) {
			dev_err(&pdev->dev, "Conflicting RTS/CTS config\n");
			ret = -EINVAL;
			goto err_clk;
		}
	}

	return ret;

err_clk:
	clk_disable_unprepare(stm32port->clk);

	return ret;
}

static struct stm32_port *stm32_usart_of_get_port(struct platform_device *pdev)
{
	struct device_node *np = pdev->dev.of_node;
	int id;

	if (!np)
		return NULL;

	id = of_alias_get_id(np, "serial");
	if (id < 0) {
		dev_err(&pdev->dev, "failed to get alias id, errno %d\n", id);
		return NULL;
	}

	if (WARN_ON(id >= STM32_MAX_PORTS))
		return NULL;

	stm32_ports[id].hw_flow_control =
		of_property_read_bool (np, "st,hw-flow-ctrl") /*deprecated*/ ||
		of_property_read_bool (np, "uart-has-rtscts");
	stm32_ports[id].port.line = id;
	stm32_ports[id].cr1_irq = USART_CR1_RXNEIE;
	stm32_ports[id].cr3_irq = 0;
	stm32_ports[id].last_res = RX_BUF_L;
	return &stm32_ports[id];
}

#ifdef CONFIG_OF
static const struct of_device_id stm32_match[] = {
	{ .compatible = "st,stm32-uart", .data = &stm32f4_info},
	{ .compatible = "st,stm32f7-uart", .data = &stm32f7_info},
	{ .compatible = "st,stm32h7-uart", .data = &stm32h7_info},
	{},
};

MODULE_DEVICE_TABLE(of, stm32_match);
#endif

static void stm32_usart_of_dma_rx_remove(struct stm32_port *stm32port,
					 struct platform_device *pdev)
{
	if (stm32port->rx_buf)
		dma_free_coherent(&pdev->dev, RX_BUF_L, stm32port->rx_buf,
				  stm32port->rx_dma_buf);
}

static int stm32_usart_of_dma_rx_probe(struct stm32_port *stm32port,
				       struct platform_device *pdev)
{
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
	struct uart_port *port = &stm32port->port;
	struct device *dev = &pdev->dev;
	struct dma_slave_config config;
	struct dma_async_tx_descriptor *desc = NULL;
	int ret;

	/*
	 * Using DMA and threaded handler for the console could lead to
	 * deadlocks.
	 */
	if (uart_console(port))
		return -ENODEV;

	stm32port->rx_buf = dma_alloc_coherent(dev, RX_BUF_L,
					       &stm32port->rx_dma_buf,
					       GFP_KERNEL);
	if (!stm32port->rx_buf)
		return -ENOMEM;

	/* Configure DMA channel */
	memset(&config, 0, sizeof(config));
	config.src_addr = port->mapbase + ofs->rdr;
	config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;

	ret = dmaengine_slave_config(stm32port->rx_ch, &config);
	if (ret < 0) {
		dev_err(dev, "rx dma channel config failed\n");
		stm32_usart_of_dma_rx_remove(stm32port, pdev);
		return ret;
	}

	/* Prepare a DMA cyclic transaction */
	desc = dmaengine_prep_dma_cyclic(stm32port->rx_ch,
					 stm32port->rx_dma_buf,
					 RX_BUF_L, RX_BUF_P, DMA_DEV_TO_MEM,
					 DMA_PREP_INTERRUPT);
	if (!desc) {
		dev_err(dev, "rx dma prep cyclic failed\n");
		stm32_usart_of_dma_rx_remove(stm32port, pdev);
		return -ENODEV;
	}

	/* Set DMA callback */
	desc->callback = stm32_usart_rx_dma_complete;
	desc->callback_param = port;

	/* Push current DMA transaction in the pending queue */
	ret = dma_submit_error(dmaengine_submit(desc));
	if (ret) {
		dmaengine_terminate_sync(stm32port->rx_ch);
		stm32_usart_of_dma_rx_remove(stm32port, pdev);
		return ret;
	}

	/* Issue pending DMA requests */
	dma_async_issue_pending(stm32port->rx_ch);

	return 0;
}

static void stm32_usart_of_dma_tx_remove(struct stm32_port *stm32port,
					 struct platform_device *pdev)
{
	if (stm32port->tx_buf)
		dma_free_coherent(&pdev->dev, TX_BUF_L, stm32port->tx_buf,
				  stm32port->tx_dma_buf);
}

static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port,
				       struct platform_device *pdev)
{
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
	struct uart_port *port = &stm32port->port;
	struct device *dev = &pdev->dev;
	struct dma_slave_config config;
	int ret;

	stm32port->tx_dma_busy = false;

	stm32port->tx_buf = dma_alloc_coherent(dev, TX_BUF_L,
					       &stm32port->tx_dma_buf,
					       GFP_KERNEL);
	if (!stm32port->tx_buf)
		return -ENOMEM;

	/* Configure DMA channel */
	memset(&config, 0, sizeof(config));
	config.dst_addr = port->mapbase + ofs->tdr;
	config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;

	ret = dmaengine_slave_config(stm32port->tx_ch, &config);
	if (ret < 0) {
		dev_err(dev, "tx dma channel config failed\n");
		stm32_usart_of_dma_tx_remove(stm32port, pdev);
		return ret;
	}

	return 0;
}

static int stm32_usart_serial_probe(struct platform_device *pdev)
{
	struct stm32_port *stm32port;
	int ret;

	stm32port = stm32_usart_of_get_port(pdev);
	if (!stm32port)
		return -ENODEV;

	stm32port->info = of_device_get_match_data(&pdev->dev);
	if (!stm32port->info)
		return -EINVAL;

	ret = stm32_usart_init_port(stm32port, pdev);
	if (ret)
		return ret;

	if (stm32port->wakeup_src) {
		device_set_wakeup_capable(&pdev->dev, true);
		ret = dev_pm_set_wake_irq(&pdev->dev, stm32port->port.irq);
		if (ret)
			goto err_deinit_port;
	}

	stm32port->rx_ch = dma_request_chan(&pdev->dev, "rx");
	if (PTR_ERR(stm32port->rx_ch) == -EPROBE_DEFER) {
		ret = -EPROBE_DEFER;
		goto err_wakeirq;
	}
	/* Fall back in interrupt mode for any non-deferral error */
	if (IS_ERR(stm32port->rx_ch))
		stm32port->rx_ch = NULL;

	stm32port->tx_ch = dma_request_chan(&pdev->dev, "tx");
	if (PTR_ERR(stm32port->tx_ch) == -EPROBE_DEFER) {
		ret = -EPROBE_DEFER;
		goto err_dma_rx;
	}
	/* Fall back in interrupt mode for any non-deferral error */
	if (IS_ERR(stm32port->tx_ch))
		stm32port->tx_ch = NULL;

	if (stm32port->rx_ch && stm32_usart_of_dma_rx_probe(stm32port, pdev)) {
		/* Fall back in interrupt mode */
		dma_release_channel(stm32port->rx_ch);
		stm32port->rx_ch = NULL;
	}

	if (stm32port->tx_ch && stm32_usart_of_dma_tx_probe(stm32port, pdev)) {
		/* Fall back in interrupt mode */
		dma_release_channel(stm32port->tx_ch);
		stm32port->tx_ch = NULL;
	}

	if (!stm32port->rx_ch)
		dev_info(&pdev->dev, "interrupt mode for rx (no dma)\n");
	if (!stm32port->tx_ch)
		dev_info(&pdev->dev, "interrupt mode for tx (no dma)\n");

	platform_set_drvdata(pdev, &stm32port->port);

	pm_runtime_get_noresume(&pdev->dev);
	pm_runtime_set_active(&pdev->dev);
	pm_runtime_enable(&pdev->dev);

	ret = uart_add_one_port(&stm32_usart_driver, &stm32port->port);
	if (ret)
		goto err_port;

	pm_runtime_put_sync(&pdev->dev);

	return 0;

err_port:
	pm_runtime_disable(&pdev->dev);
	pm_runtime_set_suspended(&pdev->dev);
	pm_runtime_put_noidle(&pdev->dev);

	if (stm32port->tx_ch) {
		stm32_usart_of_dma_tx_remove(stm32port, pdev);
		dma_release_channel(stm32port->tx_ch);
	}

	if (stm32port->rx_ch)
		stm32_usart_of_dma_rx_remove(stm32port, pdev);

err_dma_rx:
	if (stm32port->rx_ch)
		dma_release_channel(stm32port->rx_ch);

err_wakeirq:
	if (stm32port->wakeup_src)
		dev_pm_clear_wake_irq(&pdev->dev);

err_deinit_port:
	if (stm32port->wakeup_src)
		device_set_wakeup_capable(&pdev->dev, false);

	stm32_usart_deinit_port(stm32port);

	return ret;
}

static int stm32_usart_serial_remove(struct platform_device *pdev)
{
	struct uart_port *port = platform_get_drvdata(pdev);
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	int err;
	u32 cr3;

	pm_runtime_get_sync(&pdev->dev);
	err = uart_remove_one_port(&stm32_usart_driver, port);
	if (err)
		return(err);

	pm_runtime_disable(&pdev->dev);
	pm_runtime_set_suspended(&pdev->dev);
	pm_runtime_put_noidle(&pdev->dev);

	stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_PEIE);
	cr3 = readl_relaxed(port->membase + ofs->cr3);
	cr3 &= ~USART_CR3_EIE;
	cr3 &= ~USART_CR3_DMAR;
	cr3 &= ~USART_CR3_DDRE;
	writel_relaxed(cr3, port->membase + ofs->cr3);

	if (stm32_port->tx_ch) {
		dmaengine_terminate_async(stm32_port->tx_ch);
		stm32_usart_of_dma_tx_remove(stm32_port, pdev);
		dma_release_channel(stm32_port->tx_ch);
	}

	if (stm32_port->rx_ch) {
		dmaengine_terminate_async(stm32_port->rx_ch);
		stm32_usart_of_dma_rx_remove(stm32_port, pdev);
		dma_release_channel(stm32_port->rx_ch);
	}

	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

	if (stm32_port->wakeup_src) {
		dev_pm_clear_wake_irq(&pdev->dev);
		device_init_wakeup(&pdev->dev, false);
	}

	stm32_usart_deinit_port(stm32_port);

	return 0;
}

#ifdef CONFIG_SERIAL_STM32_CONSOLE
static void stm32_usart_console_putchar(struct uart_port *port, int ch)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	while (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
		cpu_relax();

	writel_relaxed(ch, port->membase + ofs->tdr);
}

static void stm32_usart_console_write(struct console *co, const char *s,
				      unsigned int cnt)
{
	struct uart_port *port = &stm32_ports[co->index].port;
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
	unsigned long flags;
	u32 old_cr1, new_cr1;
	int locked = 1;

	if (oops_in_progress)
		locked = spin_trylock_irqsave(&port->lock, flags);
	else
		spin_lock_irqsave(&port->lock, flags);

	/* Save and disable interrupts, enable the transmitter */
	old_cr1 = readl_relaxed(port->membase + ofs->cr1);
	new_cr1 = old_cr1 & ~USART_CR1_IE_MASK;
	new_cr1 |=  USART_CR1_TE | BIT(cfg->uart_enable_bit);
	writel_relaxed(new_cr1, port->membase + ofs->cr1);

	uart_console_write(port, s, cnt, stm32_usart_console_putchar);

	/* Restore interrupt state */
	writel_relaxed(old_cr1, port->membase + ofs->cr1);

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

static int stm32_usart_console_setup(struct console *co, char *options)
{
	struct stm32_port *stm32port;
	int baud = 9600;
	int bits = 8;
	int parity = 'n';
	int flow = 'n';

	if (co->index >= STM32_MAX_PORTS)
		return -ENODEV;

	stm32port = &stm32_ports[co->index];

	/*
	 * This driver does not support early console initialization
	 * (use ARM early printk support instead), so we only expect
	 * this to be called during the uart port registration when the
	 * driver gets probed and the port should be mapped at that point.
	 */
	if (stm32port->port.mapbase == 0 || !stm32port->port.membase)
		return -ENXIO;

	if (options)
		uart_parse_options(options, &baud, &parity, &bits, &flow);

	return uart_set_options(&stm32port->port, co, baud, parity, bits, flow);
}

static struct console stm32_console = {
	.name		= STM32_SERIAL_NAME,
	.device		= uart_console_device,
	.write		= stm32_usart_console_write,
	.setup		= stm32_usart_console_setup,
	.flags		= CON_PRINTBUFFER,
	.index		= -1,
	.data		= &stm32_usart_driver,
};

#define STM32_SERIAL_CONSOLE (&stm32_console)

#else
#define STM32_SERIAL_CONSOLE NULL
#endif /* CONFIG_SERIAL_STM32_CONSOLE */

static struct uart_driver stm32_usart_driver = {
	.driver_name	= DRIVER_NAME,
	.dev_name	= STM32_SERIAL_NAME,
	.major		= 0,
	.minor		= 0,
	.nr		= STM32_MAX_PORTS,
	.cons		= STM32_SERIAL_CONSOLE,
};

static void __maybe_unused stm32_usart_serial_en_wakeup(struct uart_port *port,
							bool enable)
{
	struct stm32_port *stm32_port = to_stm32_port(port);
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	if (!stm32_port->wakeup_src)
		return;

	/*
	 * Enable low-power wake-up and wake-up irq if argument is set to
	 * "enable", disable low-power wake-up and wake-up irq otherwise
	 */
	if (enable) {
		stm32_usart_set_bits(port, ofs->cr1, USART_CR1_UESM);
		stm32_usart_set_bits(port, ofs->cr3, USART_CR3_WUFIE);
	} else {
		stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_UESM);
		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_WUFIE);
	}
}

static int __maybe_unused stm32_usart_serial_suspend(struct device *dev)
{
	struct uart_port *port = dev_get_drvdata(dev);

	uart_suspend_port(&stm32_usart_driver, port);

	if (device_may_wakeup(dev) || device_wakeup_path(dev))
		stm32_usart_serial_en_wakeup(port, true);

	/*
	 * When "no_console_suspend" is enabled, keep the pinctrl default state
	 * and rely on bootloader stage to restore this state upon resume.
	 * Otherwise, apply the idle or sleep states depending on wakeup
	 * capabilities.
	 */
	if (console_suspend_enabled || !uart_console(port)) {
		if (device_may_wakeup(dev) || device_wakeup_path(dev))
			pinctrl_pm_select_idle_state(dev);
		else
			pinctrl_pm_select_sleep_state(dev);
	}

	return 0;
}

static int __maybe_unused stm32_usart_serial_resume(struct device *dev)
{
	struct uart_port *port = dev_get_drvdata(dev);

	pinctrl_pm_select_default_state(dev);

	if (device_may_wakeup(dev) || device_wakeup_path(dev))
		stm32_usart_serial_en_wakeup(port, false);

	return uart_resume_port(&stm32_usart_driver, port);
}

static int __maybe_unused stm32_usart_runtime_suspend(struct device *dev)
{
	struct uart_port *port = dev_get_drvdata(dev);
	struct stm32_port *stm32port = container_of(port,
			struct stm32_port, port);

	clk_disable_unprepare(stm32port->clk);

	return 0;
}

static int __maybe_unused stm32_usart_runtime_resume(struct device *dev)
{
	struct uart_port *port = dev_get_drvdata(dev);
	struct stm32_port *stm32port = container_of(port,
			struct stm32_port, port);

	return clk_prepare_enable(stm32port->clk);
}

static const struct dev_pm_ops stm32_serial_pm_ops = {
	SET_RUNTIME_PM_OPS(stm32_usart_runtime_suspend,
			   stm32_usart_runtime_resume, NULL)
	SET_SYSTEM_SLEEP_PM_OPS(stm32_usart_serial_suspend,
				stm32_usart_serial_resume)
};

static struct platform_driver stm32_serial_driver = {
	.probe		= stm32_usart_serial_probe,
	.remove		= stm32_usart_serial_remove,
	.driver	= {
		.name	= DRIVER_NAME,
		.pm	= &stm32_serial_pm_ops,
		.of_match_table = of_match_ptr(stm32_match),
	},
};

static int __init stm32_usart_init(void)
{
	static char banner[] __initdata = "STM32 USART driver initialized";
	int ret;

	pr_info("%s\n", banner);

	ret = uart_register_driver(&stm32_usart_driver);
	if (ret)
		return ret;

	ret = platform_driver_register(&stm32_serial_driver);
	if (ret)
		uart_unregister_driver(&stm32_usart_driver);

	return ret;
}

static void __exit stm32_usart_exit(void)
{
	platform_driver_unregister(&stm32_serial_driver);
	uart_unregister_driver(&stm32_usart_driver);
}

module_init(stm32_usart_init);
module_exit(stm32_usart_exit);

MODULE_ALIAS("platform:" DRIVER_NAME);
MODULE_DESCRIPTION("STMicroelectronics STM32 serial port driver");
MODULE_LICENSE("GPL v2");