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>

1 files changed, 20 insertions, 32 deletions

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 58d169e5c1db..8c66abcfe6ca 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -696,18 +696,23 @@ 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;
+	struct tty_port *tport = &port->state->port;
+
+	while (1) {
+		unsigned char ch;
 
-	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);
-		uart_xmit_advance(port, 1);
+
+		if (!uart_fifo_get(port, &ch))
+			break;
+
+		writel_relaxed(ch, port->membase + ofs->tdr);
 	}
 
 	/* rely on TXE irq (mask or unmask) for sending remaining data */
-	if (uart_circ_empty(xmit))
+	if (kfifo_is_empty(&tport->xmit_fifo))
 		stm32_usart_tx_interrupt_disable(port);
 	else
 		stm32_usart_tx_interrupt_enable(port);
@@ -716,7 +721,7 @@ static void stm32_usart_transmit_chars_pio(struct uart_port *port)
 static void stm32_usart_transmit_chars_dma(struct uart_port *port)
 {
 	struct stm32_port *stm32port = to_stm32_port(port);
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	struct dma_async_tx_descriptor *desc = NULL;
 	unsigned int count;
 	int ret;
@@ -728,25 +733,8 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
 		return;
 	}
 
-	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);
-	}
+	count =	kfifo_out_peek(&tport->xmit_fifo, &stm32port->tx_buf[0],
+			TX_BUF_L);
 
 	desc = dmaengine_prep_slave_single(stm32port->tx_ch,
 					   stm32port->tx_dma_buf,
@@ -792,14 +780,14 @@ 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;
+	struct tty_port *tport = &port->state->port;
 	u32 isr;
 	int ret;
 
 	if (!stm32_port->hw_flow_control &&
 	    port->rs485.flags & SER_RS485_ENABLED &&
 	    (port->x_char ||
-	     !(uart_circ_empty(xmit) || uart_tx_stopped(port)))) {
+	     !(kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)))) {
 		stm32_usart_tc_interrupt_disable(port);
 		stm32_usart_rs485_rts_enable(port);
 	}
@@ -826,7 +814,7 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
 		return;
 	}
 
-	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
+	if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) {
 		stm32_usart_tx_interrupt_disable(port);
 		return;
 	}
@@ -841,10 +829,10 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
 	else
 		stm32_usart_transmit_chars_pio(port);
 
-	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)) {
 		stm32_usart_tx_interrupt_disable(port);
 		if (!stm32_port->hw_flow_control &&
 		    port->rs485.flags & SER_RS485_ENABLED) {
@@ -967,9 +955,9 @@ static void stm32_usart_stop_tx(struct uart_port *port)
 /* There are probably characters waiting to be transmitted. */
 static void stm32_usart_start_tx(struct uart_port *port)
 {
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 
-	if (uart_circ_empty(xmit) && !port->x_char) {
+	if (kfifo_is_empty(&tport->xmit_fifo) && !port->x_char) {
 		stm32_usart_rs485_rts_disable(port);
 		return;
 	}