tty: serial: switch from circ_buf to kfifo

Switch from struct circ_buf to proper kfifo. kfifo provides much better
API, esp. when wrap-around of the buffer needs to be taken into account.
Look at pl011_dma_tx_refill() or cpm_uart_tx_pump() changes for example.

Kfifo API can also fill in scatter-gather DMA structures, so it easier
for that use case too. Look at lpuart_dma_tx() for example. Note that
not all drivers can be converted to that (like atmel_serial), they
handle DMA specially.

Note that usb-serial uses kfifo for TX for ages.

omap needed a bit more care as it needs to put a char into FIFO to start
the DMA transfer when OMAP_DMA_TX_KICK is set. In that case, we have to
do kfifo_dma_out_prepare twice: once to find out the tx_size (to find
out if it is worths to do DMA at all -- size >= 4), the second time for
the actual transfer.

All traces of circ_buf are removed from serial_core.h (and its struct
uart_state).

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Al Cooper <alcooperx@gmail.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: Kumaravel Thiagarajan <kumaravel.thiagarajan@microchip.com>
Cc: Tharun Kumar P <tharunkumar.pasumarthi@microchip.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Richard Genoud <richard.genoud@gmail.com>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Cc: Alexander Shiyan <shc_work@mail.ru>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Neil Armstrong <neil.armstrong@linaro.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Taichi Sugaya <sugaya.taichi@socionext.com>
Cc: Takao Orito <orito.takao@socionext.com>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
Cc: Pali Rohár <pali@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Alim Akhtar <alim.akhtar@samsung.com>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hammer Hsieh <hammerh0314@gmail.com>
Cc: Peter Korsgaard <jacmet@sunsite.dk>
Cc: Timur Tabi <timur@kernel.org>
Cc: Michal Simek <michal.simek@amd.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20240405060826.2521-13-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_bcm7271.c

@@ -413,20 +413,18 @@ static int stop_tx_dma(struct uart_8250_port *p)
 static int brcmuart_tx_dma(struct uart_8250_port *p)
 {
 	struct brcmuart_priv *priv = p->port.private_data;
-	struct circ_buf *xmit = &p->port.state->xmit;
+	struct tty_port *tport = &p->port.state->port;
 	u32 tx_size;
 
 	if (uart_tx_stopped(&p->port) || priv->tx_running ||
-		uart_circ_empty(xmit)) {
+		kfifo_is_empty(&tport->xmit_fifo)) {
 		return 0;
 	}
-	tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
 
 	priv->dma.tx_err = 0;
-	memcpy(priv->tx_buf, &xmit->buf[xmit->tail], tx_size);
-	uart_xmit_advance(&p->port, tx_size);
+	tx_size = uart_fifo_out(&p->port, priv->tx_buf, UART_XMIT_SIZE);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&p->port);
 
 	udma_writel(priv, REGS_DMA_TX, UDMA_TX_TRANSFER_LEN, tx_size);
@@ -540,7 +538,7 @@ static void brcmuart_tx_isr(struct uart_port *up, u32 isr)
 	struct brcmuart_priv *priv = up->private_data;
 	struct device *dev = up->dev;
 	struct uart_8250_port *port_8250 = up_to_u8250p(up);
-	struct circ_buf	*xmit = &port_8250->port.state->xmit;
+	struct tty_port *tport = &port_8250->port.state->port;
 
 	if (isr & UDMA_INTR_TX_ABORT) {
 		if (priv->tx_running)
@@ -548,7 +546,7 @@ static void brcmuart_tx_isr(struct uart_port *up, u32 isr)
 		return;
 	}
 	priv->tx_running = false;
-	if (!uart_circ_empty(xmit) && !uart_tx_stopped(up))
+	if (!kfifo_is_empty(&tport->xmit_fifo) && !uart_tx_stopped(up))
 		brcmuart_tx_dma(port_8250);
 }
 

drivers/tty/serial/8250/8250_core.c

@@ -280,7 +280,8 @@ static void serial8250_backup_timeout(struct timer_list *t)
 	 */
 	lsr = serial_lsr_in(up);
 	if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
-	    (!uart_circ_empty(&up->port.state->xmit) || up->port.x_char) &&
+	    (!kfifo_is_empty(&up->port.state->port.xmit_fifo) ||
+	     up->port.x_char) &&
 	    (lsr & UART_LSR_THRE)) {
 		iir &= ~(UART_IIR_ID | UART_IIR_NO_INT);
 		iir |= UART_IIR_THRI;

drivers/tty/serial/8250/8250_dma.c

@@ -15,7 +15,7 @@ static void __dma_tx_complete(void *param)
 {
 	struct uart_8250_port	*p = param;
 	struct uart_8250_dma	*dma = p->dma;
-	struct circ_buf		*xmit = &p->port.state->xmit;
+	struct tty_port		*tport = &p->port.state->port;
 	unsigned long	flags;
 	int		ret;
 
@@ -28,7 +28,7 @@ static void __dma_tx_complete(void *param)
 
 	uart_xmit_advance(&p->port, dma->tx_size);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&p->port);
 
 	ret = serial8250_tx_dma(p);
@@ -86,7 +86,7 @@ static void dma_rx_complete(void *param)
 int serial8250_tx_dma(struct uart_8250_port *p)
 {
 	struct uart_8250_dma		*dma = p->dma;
-	struct circ_buf			*xmit = &p->port.state->xmit;
+	struct tty_port			*tport = &p->port.state->port;
 	struct dma_async_tx_descriptor	*desc;
 	struct uart_port		*up = &p->port;
 	struct scatterlist sg;
@@ -103,18 +103,23 @@ int serial8250_tx_dma(struct uart_8250_port *p)
 		uart_xchar_out(up, UART_TX);
 	}
 
-	if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) {
+	if (uart_tx_stopped(&p->port) || kfifo_is_empty(&tport->xmit_fifo)) {
 		/* We have been called from __dma_tx_complete() */
 		return 0;
 	}
 
-	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
-
 	serial8250_do_prepare_tx_dma(p);
 
 	sg_init_table(&sg, 1);
-	sg_dma_address(&sg) = dma->tx_addr + xmit->tail;
-	sg_dma_len(&sg) = dma->tx_size;
+	/* kfifo can do more than one sg, we don't (quite yet) */
+	ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1,
+					   UART_XMIT_SIZE, dma->tx_addr);
+
+	/* we already checked empty fifo above, so there should be something */
+	if (WARN_ON_ONCE(ret != 1))
+		return 0;
+
+	dma->tx_size = sg_dma_len(&sg);
 
 	desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1,
 				       DMA_MEM_TO_DEV,
@@ -257,7 +262,7 @@ int serial8250_request_dma(struct uart_8250_port *p)
 
 	/* TX buffer */
 	dma->tx_addr = dma_map_single(dma->txchan->device->dev,
-					p->port.state->xmit.buf,
+					p->port.state->port.xmit_buf,
 					UART_XMIT_SIZE,
 					DMA_TO_DEVICE);
 	if (dma_mapping_error(dma->txchan->device->dev, dma->tx_addr)) {

drivers/tty/serial/8250/8250_exar.c

@@ -214,7 +214,7 @@ static void exar_shutdown(struct uart_port *port)
 {
 	bool tx_complete = false;
 	struct uart_8250_port *up = up_to_u8250p(port);
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	int i = 0;
 	u16 lsr;
 
@@ -225,7 +225,8 @@ static void exar_shutdown(struct uart_port *port)
 		else
 			tx_complete = false;
 		usleep_range(1000, 1100);
-	} while (!uart_circ_empty(xmit) && !tx_complete && i++ < 1000);
+	} while (!kfifo_is_empty(&tport->xmit_fifo) &&
+			!tx_complete && i++ < 1000);
 
 	serial8250_do_shutdown(port);
 }

drivers/tty/serial/8250/8250_mtk.c

@@ -199,7 +199,7 @@ static int mtk8250_startup(struct uart_port *port)
 
 	if (up->dma) {
 		data->rx_status = DMA_RX_START;
-		uart_circ_clear(&port->state->xmit);
+		kfifo_reset(&port->state->port.xmit_fifo);
 	}
 #endif
 	memset(&port->icount, 0, sizeof(port->icount));

drivers/tty/serial/8250/8250_omap.c

@@ -1094,7 +1094,7 @@ static void omap_8250_dma_tx_complete(void *param)
 {
 	struct uart_8250_port	*p = param;
 	struct uart_8250_dma	*dma = p->dma;
-	struct circ_buf		*xmit = &p->port.state->xmit;
+	struct tty_port		*tport = &p->port.state->port;
 	unsigned long		flags;
 	bool			en_thri = false;
 	struct omap8250_priv	*priv = p->port.private_data;
@@ -1113,10 +1113,10 @@ static void omap_8250_dma_tx_complete(void *param)
 		omap8250_restore_regs(p);
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&p->port);
 
-	if (!uart_circ_empty(xmit) && !uart_tx_stopped(&p->port)) {
+	if (!kfifo_is_empty(&tport->xmit_fifo) && !uart_tx_stopped(&p->port)) {
 		int ret;
 
 		ret = omap_8250_tx_dma(p);
@@ -1138,15 +1138,15 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 {
 	struct uart_8250_dma		*dma = p->dma;
 	struct omap8250_priv		*priv = p->port.private_data;
-	struct circ_buf			*xmit = &p->port.state->xmit;
+	struct tty_port			*tport = &p->port.state->port;
 	struct dma_async_tx_descriptor	*desc;
 	struct scatterlist sg;
-	unsigned int	skip_byte = 0;
+	int skip_byte = -1;
 	int ret;
 
 	if (dma->tx_running)
 		return 0;
-	if (uart_tx_stopped(&p->port) || uart_circ_empty(xmit)) {
+	if (uart_tx_stopped(&p->port) || kfifo_is_empty(&tport->xmit_fifo)) {
 
 		/*
 		 * Even if no data, we need to return an error for the two cases
@@ -1161,8 +1161,18 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 		return 0;
 	}
 
-	dma->tx_size = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+	sg_init_table(&sg, 1);
+	ret = kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1,
+					   UART_XMIT_SIZE, dma->tx_addr);
+	if (ret != 1) {
+		serial8250_clear_THRI(p);
+		return 0;
+	}
+
+	dma->tx_size = sg_dma_len(&sg);
+
 	if (priv->habit & OMAP_DMA_TX_KICK) {
+		unsigned char c;
 		u8 tx_lvl;
 
 		/*
@@ -1189,13 +1199,16 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 			ret = -EINVAL;
 			goto err;
 		}
-		skip_byte = 1;
+		if (!kfifo_get(&tport->xmit_fifo, &c)) {
+			ret = -EINVAL;
+			goto err;
+		}
+		skip_byte = c;
+		/* now we need to recompute due to kfifo_get */
+		kfifo_dma_out_prepare_mapped(&tport->xmit_fifo, &sg, 1,
+				UART_XMIT_SIZE, dma->tx_addr);
 	}
 
-	sg_init_table(&sg, 1);
-	sg_dma_address(&sg) = dma->tx_addr + xmit->tail + skip_byte;
-	sg_dma_len(&sg) = dma->tx_size - skip_byte;
-
 	desc = dmaengine_prep_slave_sg(dma->txchan, &sg, 1, DMA_MEM_TO_DEV,
 			DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!desc) {
@@ -1218,11 +1231,13 @@ static int omap_8250_tx_dma(struct uart_8250_port *p)
 		dma->tx_err = 0;
 
 	serial8250_clear_THRI(p);
-	if (skip_byte)
-		serial_out(p, UART_TX, xmit->buf[xmit->tail]);
-	return 0;
+	ret = 0;
+	goto out_skip;
 err:
 	dma->tx_err = 1;
+out_skip:
+	if (skip_byte >= 0)
+		serial_out(p, UART_TX, skip_byte);
 	return ret;
 }
 
@@ -1311,7 +1326,7 @@ static int omap_8250_dma_handle_irq(struct uart_port *port)
 	serial8250_modem_status(up);
 	if (status & UART_LSR_THRE && up->dma->tx_err) {
 		if (uart_tx_stopped(&up->port) ||
-		    uart_circ_empty(&up->port.state->xmit)) {
+		    kfifo_is_empty(&up->port.state->port.xmit_fifo)) {
 			up->dma->tx_err = 0;
 			serial8250_tx_chars(up);
 		} else  {

drivers/tty/serial/8250/8250_pci1xxxx.c

@@ -382,10 +382,10 @@ static void pci1xxxx_rx_burst(struct uart_port *port, u32 uart_status)
 }
 
 static void pci1xxxx_process_write_data(struct uart_port *port,
-					struct circ_buf *xmit,
 					int *data_empty_count,
 					u32 *valid_byte_count)
 {
+	struct tty_port *tport = &port->state->port;
 	u32 valid_burst_count = *valid_byte_count / UART_BURST_SIZE;
 
 	/*
@@ -395,41 +395,36 @@ static void pci1xxxx_process_write_data(struct uart_port *port,
 	 * one byte at a time.
 	 */
 	while (valid_burst_count) {
+		u32 c;
+
 		if (*data_empty_count - UART_BURST_SIZE < 0)
 			break;
-		if (xmit->tail > (UART_XMIT_SIZE - UART_BURST_SIZE))
+		if (kfifo_len(&tport->xmit_fifo) < UART_BURST_SIZE)
 			break;
-		writel(*(unsigned int *)&xmit->buf[xmit->tail],
-		       port->membase + UART_TX_BURST_FIFO);
+		if (WARN_ON(kfifo_out(&tport->xmit_fifo, (u8 *)&c, sizeof(c)) !=
+		    sizeof(c)))
+			break;
+		writel(c, port->membase + UART_TX_BURST_FIFO);
 		*valid_byte_count -= UART_BURST_SIZE;
 		*data_empty_count -= UART_BURST_SIZE;
 		valid_burst_count -= UART_BYTE_SIZE;
-
-		xmit->tail = (xmit->tail + UART_BURST_SIZE) &
-			     (UART_XMIT_SIZE - 1);
 	}
 
 	while (*valid_byte_count) {
-		if (*data_empty_count - UART_BYTE_SIZE < 0)
+		u8 c;
+
+		if (!kfifo_get(&tport->xmit_fifo, &c))
 			break;
-		writeb(xmit->buf[xmit->tail], port->membase +
-		       UART_TX_BYTE_FIFO);
+		writeb(c, port->membase + UART_TX_BYTE_FIFO);
 		*data_empty_count -= UART_BYTE_SIZE;
 		*valid_byte_count -= UART_BYTE_SIZE;
 
-		/*
-		 * When the tail of the circular buffer is reached, the next
-		 * byte is transferred to the beginning of the buffer.
-		 */
-		xmit->tail = (xmit->tail + UART_BYTE_SIZE) &
-			     (UART_XMIT_SIZE - 1);
-
 		/*
 		 * If there are any pending burst count, data is handled by
 		 * transmitting DWORDs at a time.
 		 */
-		if (valid_burst_count && (xmit->tail <
-		   (UART_XMIT_SIZE - UART_BURST_SIZE)))
+		if (valid_burst_count &&
+		    kfifo_len(&tport->xmit_fifo) >= UART_BURST_SIZE)
 			break;
 	}
 }
@@ -437,11 +432,9 @@ static void pci1xxxx_process_write_data(struct uart_port *port,
 static void pci1xxxx_tx_burst(struct uart_port *port, u32 uart_status)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
+	struct tty_port *tport = &port->state->port;
 	u32 valid_byte_count;
 	int data_empty_count;
-	struct circ_buf *xmit;
-
-	xmit = &port->state->xmit;
 
 	if (port->x_char) {
 		writeb(port->x_char, port->membase + UART_TX);
@@ -450,25 +443,25 @@ static void pci1xxxx_tx_burst(struct uart_port *port, u32 uart_status)
 		return;
 	}
 
-	if ((uart_tx_stopped(port)) || (uart_circ_empty(xmit))) {
+	if ((uart_tx_stopped(port)) || kfifo_is_empty(&tport->xmit_fifo)) {
 		port->ops->stop_tx(port);
 	} else {
 		data_empty_count = (pci1xxxx_read_burst_status(port) &
 				    UART_BST_STAT_TX_COUNT_MASK) >> 8;
 		do {
-			valid_byte_count = uart_circ_chars_pending(xmit);
+			valid_byte_count = kfifo_len(&tport->xmit_fifo);
 
-			pci1xxxx_process_write_data(port, xmit,
+			pci1xxxx_process_write_data(port,
 						    &data_empty_count,
 						    &valid_byte_count);
 
 			port->icount.tx++;
-			if (uart_circ_empty(xmit))
+			if (kfifo_is_empty(&tport->xmit_fifo))
 				break;
 		} while (data_empty_count && valid_byte_count);
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 	 /*
@@ -476,7 +469,8 @@ static void pci1xxxx_tx_burst(struct uart_port *port, u32 uart_status)
 	  * the HW can go idle. So we get here once again with empty FIFO and
 	  * disable the interrupt and RPM in __stop_tx()
 	  */
-	if (uart_circ_empty(xmit) && !(up->capabilities & UART_CAP_RPM))
+	if (kfifo_is_empty(&tport->xmit_fifo) &&
+	    !(up->capabilities & UART_CAP_RPM))
 		port->ops->stop_tx(port);
 }
 

drivers/tty/serial/8250/8250_port.c

@@ -1630,7 +1630,7 @@ static void serial8250_start_tx(struct uart_port *port)
 	/* Port locked to synchronize UART_IER access against the console. */
 	lockdep_assert_held_once(&port->lock);
 
-	if (!port->x_char && uart_circ_empty(&port->state->xmit))
+	if (!port->x_char && kfifo_is_empty(&port->state->port.xmit_fifo))
 		return;
 
 	serial8250_rpm_get_tx(up);
@@ -1778,7 +1778,7 @@ EXPORT_SYMBOL_GPL(serial8250_rx_chars);
 void serial8250_tx_chars(struct uart_8250_port *up)
 {
 	struct uart_port *port = &up->port;
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	int count;
 
 	if (port->x_char) {
@@ -1789,14 +1789,19 @@ void serial8250_tx_chars(struct uart_8250_port *up)
 		serial8250_stop_tx(port);
 		return;
 	}
-	if (uart_circ_empty(xmit)) {
+	if (kfifo_is_empty(&tport->xmit_fifo)) {
 		__stop_tx(up);
 		return;
 	}
 
 	count = up->tx_loadsz;
 	do {
-		serial_out(up, UART_TX, xmit->buf[xmit->tail]);
+		unsigned char c;
+
+		if (!uart_fifo_get(port, &c))
+			break;
+
+		serial_out(up, UART_TX, c);
 		if (up->bugs & UART_BUG_TXRACE) {
 			/*
 			 * The Aspeed BMC virtual UARTs have a bug where data
@@ -1809,9 +1814,7 @@ void serial8250_tx_chars(struct uart_8250_port *up)
 			 */
 			serial_in(up, UART_SCR);
 		}
-		uart_xmit_advance(port, 1);
-		if (uart_circ_empty(xmit))
-			break;
+
 		if ((up->capabilities & UART_CAP_HFIFO) &&
 		    !uart_lsr_tx_empty(serial_in(up, UART_LSR)))
 			break;
@@ -1821,7 +1824,7 @@ void serial8250_tx_chars(struct uart_8250_port *up)
 			break;
 	} while (--count > 0);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 	/*
@@ -1829,7 +1832,8 @@ void serial8250_tx_chars(struct uart_8250_port *up)
 	 * HW can go idle. So we get here once again with empty FIFO and disable
 	 * the interrupt and RPM in __stop_tx()
 	 */
-	if (uart_circ_empty(xmit) && !(up->capabilities & UART_CAP_RPM))
+	if (kfifo_is_empty(&tport->xmit_fifo) &&
+	    !(up->capabilities & UART_CAP_RPM))
 		__stop_tx(up);
 }
 EXPORT_SYMBOL_GPL(serial8250_tx_chars);

drivers/tty/serial/amba-pl011.c

@@ -535,6 +535,7 @@ static void pl011_start_tx_pio(struct uart_amba_port *uap);
 static void pl011_dma_tx_callback(void *data)
 {
 	struct uart_amba_port *uap = data;
+	struct tty_port *tport = &uap->port.state->port;
 	struct pl011_dmatx_data *dmatx = &uap->dmatx;
 	unsigned long flags;
 	u16 dmacr;
@@ -558,7 +559,7 @@ static void pl011_dma_tx_callback(void *data)
 	 * get further refills (hence we check dmacr).
 	 */
 	if (!(dmacr & UART011_TXDMAE) || uart_tx_stopped(&uap->port) ||
-	    uart_circ_empty(&uap->port.state->xmit)) {
+	    kfifo_is_empty(&tport->xmit_fifo)) {
 		uap->dmatx.queued = false;
 		uart_port_unlock_irqrestore(&uap->port, flags);
 		return;
@@ -588,7 +589,7 @@ static int pl011_dma_tx_refill(struct uart_amba_port *uap)
 	struct dma_chan *chan = dmatx->chan;
 	struct dma_device *dma_dev = chan->device;
 	struct dma_async_tx_descriptor *desc;
-	struct circ_buf *xmit = &uap->port.state->xmit;
+	struct tty_port *tport = &uap->port.state->port;
 	unsigned int count;
 
 	/*
@@ -597,7 +598,7 @@ static int pl011_dma_tx_refill(struct uart_amba_port *uap)
 	 * the standard interrupt handling.  This ensures that we
 	 * issue a uart_write_wakeup() at the appropriate time.
 	 */
-	count = uart_circ_chars_pending(xmit);
+	count = kfifo_len(&tport->xmit_fifo);
 	if (count < (uap->fifosize >> 1)) {
 		uap->dmatx.queued = false;
 		return 0;
@@ -613,21 +614,7 @@ static int pl011_dma_tx_refill(struct uart_amba_port *uap)
 	if (count > PL011_DMA_BUFFER_SIZE)
 		count = PL011_DMA_BUFFER_SIZE;
 
-	if (xmit->tail < xmit->head) {
-		memcpy(&dmatx->buf[0], &xmit->buf[xmit->tail], count);
-	} else {
-		size_t first = UART_XMIT_SIZE - xmit->tail;
-		size_t second;
-
-		if (first > count)
-			first = count;
-		second = count - first;
-
-		memcpy(&dmatx->buf[0], &xmit->buf[xmit->tail], first);
-		if (second)
-			memcpy(&dmatx->buf[first], &xmit->buf[0], second);
-	}
-
+	count = kfifo_out_peek(&tport->xmit_fifo, dmatx->buf, count);
 	dmatx->len = count;
 	dmatx->dma = dma_map_single(dma_dev->dev, dmatx->buf, count,
 				    DMA_TO_DEVICE);
@@ -670,7 +657,7 @@ static int pl011_dma_tx_refill(struct uart_amba_port *uap)
 	 */
 	uart_xmit_advance(&uap->port, count);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&uap->port);
 
 	return 1;
@@ -1454,7 +1441,7 @@ static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
 /* Returns true if tx interrupts have to be (kept) enabled  */
 static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 {
-	struct circ_buf *xmit = &uap->port.state->xmit;
+	struct tty_port *tport = &uap->port.state->port;
 	int count = uap->fifosize >> 1;
 
 	if (uap->port.x_char) {
@@ -1463,7 +1450,7 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 		uap->port.x_char = 0;
 		--count;
 	}
-	if (uart_circ_empty(xmit) || uart_tx_stopped(&uap->port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(&uap->port)) {
 		pl011_stop_tx(&uap->port);
 		return false;
 	}
@@ -1472,20 +1459,25 @@ static bool pl011_tx_chars(struct uart_amba_port *uap, bool from_irq)
 	if (pl011_dma_tx_irq(uap))
 		return true;
 
-	do {
+	while (1) {
+		unsigned char c;
+
 		if (likely(from_irq) && count-- == 0)
 			break;
 
-		if (!pl011_tx_char(uap, xmit->buf[xmit->tail], from_irq))
+		if (!kfifo_peek(&tport->xmit_fifo, &c))
 			break;
 
-		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
-	} while (!uart_circ_empty(xmit));
+		if (!pl011_tx_char(uap, c, from_irq))
+			break;
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		kfifo_skip(&tport->xmit_fifo);
+	}
+
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&uap->port);
 
-	if (uart_circ_empty(xmit)) {
+	if (kfifo_is_empty(&tport->xmit_fifo)) {
 		pl011_stop_tx(&uap->port);
 		return false;
 	}

drivers/tty/serial/ar933x_uart.c

@@ -390,7 +390,7 @@ static void ar933x_uart_rx_chars(struct ar933x_uart_port *up)
 
 static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 {
-	struct circ_buf *xmit = &up->port.state->xmit;
+	struct tty_port *tport = &up->port.state->port;
 	struct serial_rs485 *rs485conf = &up->port.rs485;
 	int count;
 	bool half_duplex_send = false;
@@ -399,7 +399,7 @@ static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 		return;
 
 	if ((rs485conf->flags & SER_RS485_ENABLED) &&
-	    (up->port.x_char || !uart_circ_empty(xmit))) {
+	    (up->port.x_char || !kfifo_is_empty(&tport->xmit_fifo))) {
 		ar933x_uart_stop_rx_interrupt(up);
 		gpiod_set_value(up->rts_gpiod, !!(rs485conf->flags & SER_RS485_RTS_ON_SEND));
 		half_duplex_send = true;
@@ -408,6 +408,7 @@ static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 	count = up->port.fifosize;
 	do {
 		unsigned int rdata;
+		unsigned char c;
 
 		rdata = ar933x_uart_read(up, AR933X_UART_DATA_REG);
 		if ((rdata & AR933X_UART_DATA_TX_CSR) == 0)
@@ -420,18 +421,16 @@ static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 			continue;
 		}
 
-		if (uart_circ_empty(xmit))
+		if (!uart_fifo_get(&up->port, &c))
 			break;
 
-		ar933x_uart_putc(up, xmit->buf[xmit->tail]);
-
-		uart_xmit_advance(&up->port, 1);
+		ar933x_uart_putc(up, c);
 	} while (--count > 0);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&up->port);
 
-	if (!uart_circ_empty(xmit)) {
+	if (!kfifo_is_empty(&tport->xmit_fifo)) {
 		ar933x_uart_start_tx_interrupt(up);
 	} else if (half_duplex_send) {
 		ar933x_uart_wait_tx_complete(up);

drivers/tty/serial/arc_uart.c

@@ -155,7 +155,7 @@ static unsigned int arc_serial_tx_empty(struct uart_port *port)
  */
 static void arc_serial_tx_chars(struct uart_port *port)
 {
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	int sent = 0;
 	unsigned char ch;
 
@@ -164,9 +164,7 @@ static void arc_serial_tx_chars(struct uart_port *port)
 		port->icount.tx++;
 		port->x_char = 0;
 		sent = 1;
-	} else if (!uart_circ_empty(xmit)) {
-		ch = xmit->buf[xmit->tail];
-		uart_xmit_advance(port, 1);
+	} else if (uart_fifo_get(port, &ch)) {
 		while (!(UART_GET_STATUS(port) & TXEMPTY))
 			cpu_relax();
 		UART_SET_DATA(port, ch);
@@ -177,7 +175,7 @@ static void arc_serial_tx_chars(struct uart_port *port)
 	 * If num chars in xmit buffer are too few, ask tty layer for more.
 	 * By Hard ISR to schedule processing in software interrupt part
 	 */
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 	if (sent)

drivers/tty/serial/atmel_serial.c

@@ -857,7 +857,7 @@ 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 tty_port *tport = &port->state->port;
 	struct dma_chan *chan = atmel_port->chan_tx;
 	unsigned long flags;
 
@@ -873,15 +873,15 @@ static void atmel_complete_tx_dma(void *arg)
 	atmel_port->desc_tx = NULL;
 	spin_unlock(&atmel_port->lock_tx);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 	/*
-	 * xmit is a circular buffer so, if we have just send data from
-	 * xmit->tail to the end of xmit->buf, now we have to transmit the
-	 * remaining data from the beginning of xmit->buf to xmit->head.
+	 * xmit is a circular buffer so, if we have just send data from the
+	 * tail to the end, now we have to transmit the remaining data from the
+	 * beginning to the head.
 	 */
-	if (!uart_circ_empty(xmit))
+	if (!kfifo_is_empty(&tport->xmit_fifo))
 		atmel_tasklet_schedule(atmel_port, &atmel_port->tasklet_tx);
 	else if (atmel_uart_is_half_duplex(port)) {
 		/*
@@ -919,18 +919,18 @@ static void atmel_release_tx_dma(struct uart_port *port)
 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 tty_port *tport = &port->state->port;
 	struct dma_chan *chan = atmel_port->chan_tx;
 	struct dma_async_tx_descriptor *desc;
 	struct scatterlist sgl[2], *sg, *sg_tx = &atmel_port->sg_tx;
-	unsigned int tx_len, part1_len, part2_len, sg_len;
+	unsigned int tx_len, tail, part1_len, part2_len, sg_len;
 	dma_addr_t phys_addr;
 
 	/* Make sure we have an idle channel */
 	if (atmel_port->desc_tx != NULL)
 		return;
 
-	if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
+	if (!kfifo_is_empty(&tport->xmit_fifo) && !uart_tx_stopped(port)) {
 		/*
 		 * DMA is idle now.
 		 * Port xmit buffer is already mapped,
@@ -940,9 +940,8 @@ static void atmel_tx_dma(struct uart_port *port)
 		 * Take the port lock to get a
 		 * consistent xmit buffer state.
 		 */
-		tx_len = CIRC_CNT_TO_END(xmit->head,
-					 xmit->tail,
-					 UART_XMIT_SIZE);
+		tx_len = kfifo_out_linear(&tport->xmit_fifo, &tail,
+				UART_XMIT_SIZE);
 
 		if (atmel_port->fifo_size) {
 			/* multi data mode */
@@ -956,7 +955,7 @@ static void atmel_tx_dma(struct uart_port *port)
 
 		sg_init_table(sgl, 2);
 		sg_len = 0;
-		phys_addr = sg_dma_address(sg_tx) + xmit->tail;
+		phys_addr = sg_dma_address(sg_tx) + tail;
 		if (part1_len) {
 			sg = &sgl[sg_len++];
 			sg_dma_address(sg) = phys_addr;
@@ -973,7 +972,7 @@ static void atmel_tx_dma(struct uart_port *port)
 
 		/*
 		 * save tx_len so atmel_complete_tx_dma() will increase
-		 * xmit->tail correctly
+		 * tail correctly
 		 */
 		atmel_port->tx_len = tx_len;
 
@@ -1003,13 +1002,14 @@ static void atmel_tx_dma(struct uart_port *port)
 		dma_async_issue_pending(chan);
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < 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);
+	struct tty_port *tport = &port->state->port;
 	struct device *mfd_dev = port->dev->parent;
 	dma_cap_mask_t		mask;
 	struct dma_slave_config config;
@@ -1031,11 +1031,11 @@ static int atmel_prepare_tx_dma(struct uart_port *port)
 	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(!PAGE_ALIGNED(port->state->xmit.buf));
+	BUG_ON(!PAGE_ALIGNED(tport->xmit_buf));
 	sg_set_page(&atmel_port->sg_tx,
-			virt_to_page(port->state->xmit.buf),
+			virt_to_page(tport->xmit_buf),
 			UART_XMIT_SIZE,
-			offset_in_page(port->state->xmit.buf));
+			offset_in_page(tport->xmit_buf));
 	nent = dma_map_sg(port->dev,
 				&atmel_port->sg_tx,
 				1,
@@ -1047,7 +1047,7 @@ static int atmel_prepare_tx_dma(struct uart_port *port)
 	} else {
 		dev_dbg(port->dev, "%s: mapped %d@%p to %pad\n", __func__,
 			sg_dma_len(&atmel_port->sg_tx),
-			port->state->xmit.buf,
+			tport->xmit_buf,
 			&sg_dma_address(&atmel_port->sg_tx));
 	}
 
@@ -1459,9 +1459,8 @@ static void atmel_release_tx_pdc(struct uart_port *port)
 static void atmel_tx_pdc(struct uart_port *port)
 {
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
-	int count;
 
 	/* nothing left to transmit? */
 	if (atmel_uart_readl(port, ATMEL_PDC_TCR))
@@ -1474,17 +1473,19 @@ static void atmel_tx_pdc(struct uart_port *port)
 	/* disable PDC transmit */
 	atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS);
 
-	if (!uart_circ_empty(xmit) && !uart_tx_stopped(port)) {
+	if (!kfifo_is_empty(&tport->xmit_fifo) && !uart_tx_stopped(port)) {
+		unsigned int count, tail;
+
 		dma_sync_single_for_device(port->dev,
 					   pdc->dma_addr,
 					   pdc->dma_size,
 					   DMA_TO_DEVICE);
 
-		count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+		count = kfifo_out_linear(&tport->xmit_fifo, &tail,
+				UART_XMIT_SIZE);
 		pdc->ofs = count;
 
-		atmel_uart_writel(port, ATMEL_PDC_TPR,
-				  pdc->dma_addr + xmit->tail);
+		atmel_uart_writel(port, ATMEL_PDC_TPR, pdc->dma_addr + tail);
 		atmel_uart_writel(port, ATMEL_PDC_TCR, count);
 		/* re-enable PDC transmit */
 		atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTEN);
@@ -1498,7 +1499,7 @@ static void atmel_tx_pdc(struct uart_port *port)
 		}
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 }
 
@@ -1506,9 +1507,9 @@ static int atmel_prepare_tx_pdc(struct uart_port *port)
 {
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
 	struct atmel_dma_buffer *pdc = &atmel_port->pdc_tx;
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 
-	pdc->buf = xmit->buf;
+	pdc->buf = tport->xmit_buf;
 	pdc->dma_addr = dma_map_single(port->dev,
 					pdc->buf,
 					UART_XMIT_SIZE,

drivers/tty/serial/clps711x.c

@@ -146,7 +146,8 @@ static irqreturn_t uart_clps711x_int_tx(int irq, void *dev_id)
 {
 	struct uart_port *port = dev_id;
 	struct clps711x_port *s = dev_get_drvdata(port->dev);
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
+	unsigned char c;
 
 	if (port->x_char) {
 		writew(port->x_char, port->membase + UARTDR_OFFSET);
@@ -155,7 +156,7 @@ static irqreturn_t uart_clps711x_int_tx(int irq, void *dev_id)
 		return IRQ_HANDLED;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) {
 		if (s->tx_enabled) {
 			disable_irq_nosync(port->irq);
 			s->tx_enabled = 0;
@@ -163,18 +164,17 @@ static irqreturn_t uart_clps711x_int_tx(int irq, void *dev_id)
 		return IRQ_HANDLED;
 	}
 
-	while (!uart_circ_empty(xmit)) {
+	while (uart_fifo_get(port, &c)) {
 		u32 sysflg = 0;
 
-		writew(xmit->buf[xmit->tail], port->membase + UARTDR_OFFSET);
-		uart_xmit_advance(port, 1);
+		writew(c, port->membase + UARTDR_OFFSET);
 
 		regmap_read(s->syscon, SYSFLG_OFFSET, &sysflg);
 		if (sysflg & SYSFLG_UTXFF)
 			break;
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 	return IRQ_HANDLED;

drivers/tty/serial/cpm_uart.c

@@ -648,7 +648,7 @@ static int cpm_uart_tx_pump(struct uart_port *port)
 	int count;
 	struct uart_cpm_port *pinfo =
 		container_of(port, struct uart_cpm_port, port);
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 
 	/* Handle xon/xoff */
 	if (port->x_char) {
@@ -673,7 +673,7 @@ static int cpm_uart_tx_pump(struct uart_port *port)
 		return 1;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) {
 		cpm_uart_stop_tx(port);
 		return 0;
 	}
@@ -681,16 +681,10 @@ static int cpm_uart_tx_pump(struct uart_port *port)
 	/* Pick next descriptor and fill from buffer */
 	bdp = pinfo->tx_cur;
 
-	while (!(in_be16(&bdp->cbd_sc) & BD_SC_READY) && !uart_circ_empty(xmit)) {
-		count = 0;
+	while (!(in_be16(&bdp->cbd_sc) & BD_SC_READY) &&
+			!kfifo_is_empty(&tport->xmit_fifo)) {
 		p = cpm2cpu_addr(in_be32(&bdp->cbd_bufaddr), pinfo);
-		while (count < pinfo->tx_fifosize) {
-			*p++ = xmit->buf[xmit->tail];
-			uart_xmit_advance(port, 1);
-			count++;
-			if (uart_circ_empty(xmit))
-				break;
-		}
+		count = uart_fifo_out(port, p, pinfo->tx_fifosize);
 		out_be16(&bdp->cbd_datlen, count);
 		setbits16(&bdp->cbd_sc, BD_SC_READY);
 		/* Get next BD. */
@@ -701,10 +695,10 @@ static int cpm_uart_tx_pump(struct uart_port *port)
 	}
 	pinfo->tx_cur = bdp;
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
-	if (uart_circ_empty(xmit)) {
+	if (kfifo_is_empty(&tport->xmit_fifo)) {
 		cpm_uart_stop_tx(port);
 		return 0;
 	}

drivers/tty/serial/digicolor-usart.c

@@ -179,8 +179,9 @@ static void digicolor_uart_rx(struct uart_port *port)
 
 static void digicolor_uart_tx(struct uart_port *port)
 {
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	unsigned long flags;
+	unsigned char c;
 
 	if (digicolor_uart_tx_full(port))
 		return;
@@ -194,20 +195,19 @@ static void digicolor_uart_tx(struct uart_port *port)
 		goto out;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) {
 		digicolor_uart_stop_tx(port);
 		goto out;
 	}
 
-	while (!uart_circ_empty(xmit)) {
-		writeb(xmit->buf[xmit->tail], port->membase + UA_EMI_REC);
-		uart_xmit_advance(port, 1);
+	while (uart_fifo_get(port, &c)) {
+		writeb(c, port->membase + UA_EMI_REC);
 
 		if (digicolor_uart_tx_full(port))
 			break;
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 
 out:

drivers/tty/serial/dz.c

@@ -252,13 +252,13 @@ static inline void dz_receive_chars(struct dz_mux *mux)
 static inline void dz_transmit_chars(struct dz_mux *mux)
 {
 	struct dz_port *dport = &mux->dport[0];
-	struct circ_buf *xmit;
+	struct tty_port *tport;
 	unsigned char tmp;
 	u16 status;
 
 	status = dz_in(dport, DZ_CSR);
 	dport = &mux->dport[LINE(status)];
-	xmit = &dport->port.state->xmit;
+	tport = &dport->port.state->port;
 
 	if (dport->port.x_char) {		/* XON/XOFF chars */
 		dz_out(dport, DZ_TDR, dport->port.x_char);
@@ -267,7 +267,8 @@ static inline void dz_transmit_chars(struct dz_mux *mux)
 		return;
 	}
 	/* If nothing to do or stopped or hardware stopped. */
-	if (uart_circ_empty(xmit) || uart_tx_stopped(&dport->port)) {
+	if (uart_tx_stopped(&dport->port) ||
+			!uart_fifo_get(&dport->port, &tmp)) {
 		uart_port_lock(&dport->port);
 		dz_stop_tx(&dport->port);
 		uart_port_unlock(&dport->port);
@@ -278,15 +279,13 @@ static inline void dz_transmit_chars(struct dz_mux *mux)
 	 * If something to do... (remember the dz has no output fifo,
 	 * so we go one char at a time) :-<
 	 */
-	tmp = xmit->buf[xmit->tail];
 	dz_out(dport, DZ_TDR, tmp);
-	uart_xmit_advance(&dport->port, 1);
 
-	if (uart_circ_chars_pending(xmit) < DZ_WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < DZ_WAKEUP_CHARS)
 		uart_write_wakeup(&dport->port);
 
 	/* Are we are done. */
-	if (uart_circ_empty(xmit)) {
+	if (kfifo_is_empty(&tport->xmit_fifo)) {
 		uart_port_lock(&dport->port);
 		dz_stop_tx(&dport->port);
 		uart_port_unlock(&dport->port);

drivers/tty/serial/fsl_linflexuart.c

@@ -174,17 +174,18 @@ static void linflex_put_char(struct uart_port *sport, unsigned char c)
 
 static inline void linflex_transmit_buffer(struct uart_port *sport)
 {
-	struct circ_buf *xmit = &sport->state->xmit;
+	struct tty_port *tport = &sport->state->port;
+	unsigned char c;
 
-	while (!uart_circ_empty(xmit)) {
-		linflex_put_char(sport, xmit->buf[xmit->tail]);
-		uart_xmit_advance(sport, 1);
+	while (uart_fifo_get(sport, &c)) {
+		linflex_put_char(sport, c);
+		sport->icount.tx++;
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(sport);
 
-	if (uart_circ_empty(xmit))
+	if (kfifo_is_empty(&tport->xmit_fifo))
 		linflex_stop_tx(sport);
 }
 
@@ -200,7 +201,7 @@ static void linflex_start_tx(struct uart_port *port)
 static irqreturn_t linflex_txint(int irq, void *dev_id)
 {
 	struct uart_port *sport = dev_id;
-	struct circ_buf *xmit = &sport->state->xmit;
+	struct tty_port *tport = &sport->state->port;
 	unsigned long flags;
 
 	uart_port_lock_irqsave(sport, &flags);
@@ -210,7 +211,7 @@ static irqreturn_t linflex_txint(int irq, void *dev_id)
 		goto out;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(sport)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(sport)) {
 		linflex_stop_tx(sport);
 		goto out;
 	}

drivers/tty/serial/fsl_lpuart.c

@@ -7,6 +7,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/bits.h>
+#include <linux/circ_buf.h>
 #include <linux/clk.h>
 #include <linux/console.h>
 #include <linux/delay.h>
@@ -473,7 +474,7 @@ static void lpuart32_stop_rx(struct uart_port *port)
 
 static void lpuart_dma_tx(struct lpuart_port *sport)
 {
-	struct circ_buf *xmit = &sport->port.state->xmit;
+	struct tty_port *tport = &sport->port.state->port;
 	struct scatterlist *sgl = sport->tx_sgl;
 	struct device *dev = sport->port.dev;
 	struct dma_chan *chan = sport->dma_tx_chan;
@@ -482,18 +483,10 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
 	if (sport->dma_tx_in_progress)
 		return;
 
-	sport->dma_tx_bytes = uart_circ_chars_pending(xmit);
-
-	if (xmit->tail < xmit->head || xmit->head == 0) {
-		sport->dma_tx_nents = 1;
-		sg_init_one(sgl, xmit->buf + xmit->tail, sport->dma_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);
-	}
+	sg_init_table(sgl, ARRAY_SIZE(sport->tx_sgl));
+	sport->dma_tx_bytes = kfifo_len(&tport->xmit_fifo);
+	sport->dma_tx_nents = kfifo_dma_out_prepare(&tport->xmit_fifo, sgl,
+			ARRAY_SIZE(sport->tx_sgl), sport->dma_tx_bytes);
 
 	ret = dma_map_sg(chan->device->dev, sgl, sport->dma_tx_nents,
 			 DMA_TO_DEVICE);
@@ -521,14 +514,15 @@ static void lpuart_dma_tx(struct lpuart_port *sport)
 
 static bool lpuart_stopped_or_empty(struct uart_port *port)
 {
-	return uart_circ_empty(&port->state->xmit) || uart_tx_stopped(port);
+	return kfifo_is_empty(&port->state->port.xmit_fifo) ||
+		uart_tx_stopped(port);
 }
 
 static void lpuart_dma_tx_complete(void *arg)
 {
 	struct lpuart_port *sport = arg;
 	struct scatterlist *sgl = &sport->tx_sgl[0];
-	struct circ_buf *xmit = &sport->port.state->xmit;
+	struct tty_port *tport = &sport->port.state->port;
 	struct dma_chan *chan = sport->dma_tx_chan;
 	unsigned long flags;
 
@@ -545,7 +539,7 @@ static void lpuart_dma_tx_complete(void *arg)
 	sport->dma_tx_in_progress = false;
 	uart_port_unlock_irqrestore(&sport->port, flags);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&sport->port);
 
 	if (waitqueue_active(&sport->dma_wait)) {
@@ -756,8 +750,9 @@ static inline void lpuart_transmit_buffer(struct lpuart_port *sport)
 
 static inline void lpuart32_transmit_buffer(struct lpuart_port *sport)
 {
-	struct circ_buf *xmit = &sport->port.state->xmit;
+	struct tty_port *tport = &sport->port.state->port;
 	unsigned long txcnt;
+	unsigned char c;
 
 	if (sport->port.x_char) {
 		lpuart32_write(&sport->port, sport->port.x_char, UARTDATA);
@@ -774,18 +769,18 @@ static inline void lpuart32_transmit_buffer(struct lpuart_port *sport)
 	txcnt = lpuart32_read(&sport->port, UARTWATER);
 	txcnt = txcnt >> UARTWATER_TXCNT_OFF;
 	txcnt &= UARTWATER_COUNT_MASK;
-	while (!uart_circ_empty(xmit) && (txcnt < sport->txfifo_size)) {
-		lpuart32_write(&sport->port, xmit->buf[xmit->tail], UARTDATA);
-		uart_xmit_advance(&sport->port, 1);
+	while (txcnt < sport->txfifo_size &&
+			uart_fifo_get(&sport->port, &c)) {
+		lpuart32_write(&sport->port, c, UARTDATA);
 		txcnt = lpuart32_read(&sport->port, UARTWATER);
 		txcnt = txcnt >> UARTWATER_TXCNT_OFF;
 		txcnt &= UARTWATER_COUNT_MASK;
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&sport->port);
 
-	if (uart_circ_empty(xmit))
+	if (kfifo_is_empty(&tport->xmit_fifo))
 		lpuart32_stop_tx(&sport->port);
 }
 

drivers/tty/serial/icom.c

@@ -877,10 +877,10 @@ unlock:
 static int icom_write(struct uart_port *port)
 {
 	struct icom_port *icom_port = to_icom_port(port);
+	struct tty_port *tport = &port->state->port;
 	unsigned long data_count;
 	unsigned char cmdReg;
 	unsigned long offset;
-	int temp_tail = port->state->xmit.tail;
 
 	trace(icom_port, "WRITE", 0);
 
@@ -890,16 +890,8 @@ static int icom_write(struct uart_port *port)
 		return 0;
 	}
 
-	data_count = 0;
-	while ((port->state->xmit.head != temp_tail) &&
-	       (data_count <= XMIT_BUFF_SZ)) {
-
-		icom_port->xmit_buf[data_count++] =
-		    port->state->xmit.buf[temp_tail];
-
-		temp_tail++;
-		temp_tail &= (UART_XMIT_SIZE - 1);
-	}
+	data_count = kfifo_out_peek(&tport->xmit_fifo, icom_port->xmit_buf,
+			XMIT_BUFF_SZ);
 
 	if (data_count) {
 		icom_port->statStg->xmit[0].flags =
@@ -956,7 +948,8 @@ static inline void check_modem_status(struct icom_port *icom_port)
 
 static void xmit_interrupt(u16 port_int_reg, struct icom_port *icom_port)
 {
-	u16 count, i;
+	struct tty_port *tport = &icom_port->uart_port.state->port;
+	u16 count;
 
 	if (port_int_reg & (INT_XMIT_COMPLETED)) {
 		trace(icom_port, "XMIT_COMPLETE", 0);
@@ -968,13 +961,7 @@ static void xmit_interrupt(u16 port_int_reg, struct icom_port *icom_port)
 		count = le16_to_cpu(icom_port->statStg->xmit[0].leLength);
 		icom_port->uart_port.icount.tx += count;
 
-		for (i=0; i<count &&
-			!uart_circ_empty(&icom_port->uart_port.state->xmit); i++) {
-
-			icom_port->uart_port.state->xmit.tail++;
-			icom_port->uart_port.state->xmit.tail &=
-				(UART_XMIT_SIZE - 1);
-		}
+		kfifo_skip_count(&tport->xmit_fifo, count);
 
 		if (!icom_write(&icom_port->uart_port))
 			/* activate write queue */

drivers/tty/serial/imx.c

@@ -8,6 +8,7 @@
  * Copyright (C) 2004 Pengutronix
  */
 
+#include <linux/circ_buf.h>
 #include <linux/module.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
@@ -521,7 +522,8 @@ 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;
+	struct tty_port *tport = &sport->port.state->port;
+	unsigned char c;
 
 	if (sport->port.x_char) {
 		/* Send next char */
@@ -531,7 +533,8 @@ static inline void imx_uart_transmit_buffer(struct imx_port *sport)
 		return;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(&sport->port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) ||
+			uart_tx_stopped(&sport->port)) {
 		imx_uart_stop_tx(&sport->port);
 		return;
 	}
@@ -555,26 +558,22 @@ static inline void imx_uart_transmit_buffer(struct imx_port *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);
-		uart_xmit_advance(&sport->port, 1);
-	}
+	while (!(imx_uart_readl(sport, imx_uart_uts_reg(sport)) & UTS_TXFULL) &&
+			uart_fifo_get(&sport->port, &c))
+		imx_uart_writel(sport, c, URTX0);
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&sport->port);
 
-	if (uart_circ_empty(xmit))
+	if (kfifo_is_empty(&tport->xmit_fifo))
 		imx_uart_stop_tx(&sport->port);
 }
 
 static void imx_uart_dma_tx_callback(void *data)
 {
 	struct imx_port *sport = data;
+	struct tty_port *tport = &sport->port.state->port;
 	struct scatterlist *sgl = &sport->tx_sgl[0];
-	struct circ_buf *xmit = &sport->port.state->xmit;
 	unsigned long flags;
 	u32 ucr1;
 
@@ -592,10 +591,11 @@ static void imx_uart_dma_tx_callback(void *data)
 
 	sport->dma_is_txing = 0;
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&sport->port);
 
-	if (!uart_circ_empty(xmit) && !uart_tx_stopped(&sport->port))
+	if (!kfifo_is_empty(&tport->xmit_fifo) &&
+			!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);
@@ -609,7 +609,7 @@ static void imx_uart_dma_tx_callback(void *data)
 /* 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 tty_port *tport = &sport->port.state->port;
 	struct scatterlist *sgl = sport->tx_sgl;
 	struct dma_async_tx_descriptor *desc;
 	struct dma_chan	*chan = sport->dma_chan_tx;
@@ -624,18 +624,10 @@ static void imx_uart_dma_tx(struct imx_port *sport)
 	ucr4 &= ~UCR4_TCEN;
 	imx_uart_writel(sport, ucr4, UCR4);
 
-	sport->tx_bytes = uart_circ_chars_pending(xmit);
-
-	if (xmit->tail < xmit->head || xmit->head == 0) {
-		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);
-	}
+	sg_init_table(sgl, ARRAY_SIZE(sport->tx_sgl));
+	sport->tx_bytes = kfifo_len(&tport->xmit_fifo);
+	sport->dma_tx_nents = kfifo_dma_out_prepare(&tport->xmit_fifo, sgl,
+			ARRAY_SIZE(sport->tx_sgl), sport->tx_bytes);
 
 	ret = dma_map_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
 	if (ret == 0) {
@@ -653,8 +645,7 @@ static void imx_uart_dma_tx(struct imx_port *sport)
 	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));
+	dev_dbg(dev, "TX: prepare to send %u bytes by DMA.\n", sport->tx_bytes);
 
 	ucr1 = imx_uart_readl(sport, UCR1);
 	ucr1 |= UCR1_TXDMAEN;
@@ -671,9 +662,10 @@ static void imx_uart_dma_tx(struct imx_port *sport)
 static void imx_uart_start_tx(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
+	struct tty_port *tport = &sport->port.state->port;
 	u32 ucr1;
 
-	if (!sport->port.x_char && uart_circ_empty(&port->state->xmit))
+	if (!sport->port.x_char && kfifo_is_empty(&tport->xmit_fifo))
 		return;
 
 	/*
@@ -749,7 +741,7 @@ static void imx_uart_start_tx(struct uart_port *port)
 			return;
 		}
 
-		if (!uart_circ_empty(&port->state->xmit) &&
+		if (!kfifo_is_empty(&tport->xmit_fifo) &&
 		    !uart_tx_stopped(port))
 			imx_uart_dma_tx(sport);
 		return;