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, 21 insertions, 35 deletions

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index ff85ebd3a007..3c0931fba1c6 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -272,9 +272,10 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 		return -ENOMEM;
 
 	uart_port_lock(state, flags);
-	if (!state->xmit.buf) {
-		state->xmit.buf = (unsigned char *) page;
-		uart_circ_clear(&state->xmit);
+	if (!state->port.xmit_buf) {
+		state->port.xmit_buf = (unsigned char *)page;
+		kfifo_init(&state->port.xmit_fifo, state->port.xmit_buf,
+				PAGE_SIZE);
 		uart_port_unlock(uport, flags);
 	} else {
 		uart_port_unlock(uport, flags);
@@ -387,8 +388,9 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 	 * can endup in printk() recursion.
 	 */
 	uart_port_lock(state, flags);
-	xmit_buf = state->xmit.buf;
-	state->xmit.buf = NULL;
+	xmit_buf = port->xmit_buf;
+	port->xmit_buf = NULL;
+	INIT_KFIFO(port->xmit_fifo);
 	uart_port_unlock(uport, flags);
 
 	free_page((unsigned long)xmit_buf);
@@ -552,22 +554,17 @@ static int uart_put_char(struct tty_struct *tty, u8 c)
 {
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port;
-	struct circ_buf *circ;
 	unsigned long flags;
 	int ret = 0;
 
-	circ = &state->xmit;
 	port = uart_port_lock(state, flags);
-	if (!circ->buf) {
+	if (WARN_ON_ONCE(!state->port.xmit_buf)) {
 		uart_port_unlock(port, flags);
 		return 0;
 	}
 
-	if (port && uart_circ_chars_free(circ) != 0) {
-		circ->buf[circ->head] = c;
-		circ->head = (circ->head + 1) & (UART_XMIT_SIZE - 1);
-		ret = 1;
-	}
+	if (port)
+		ret = kfifo_put(&state->port.xmit_fifo, c);
 	uart_port_unlock(port, flags);
 	return ret;
 }
@@ -581,9 +578,8 @@ static ssize_t uart_write(struct tty_struct *tty, const u8 *buf, size_t count)
 {
 	struct uart_state *state = tty->driver_data;
 	struct uart_port *port;
-	struct circ_buf *circ;
 	unsigned long flags;
-	int c, ret = 0;
+	int ret = 0;
 
 	/*
 	 * This means you called this function _after_ the port was
@@ -593,24 +589,13 @@ static ssize_t uart_write(struct tty_struct *tty, const u8 *buf, size_t count)
 		return -EL3HLT;
 
 	port = uart_port_lock(state, flags);
-	circ = &state->xmit;
-	if (!circ->buf) {
+	if (WARN_ON_ONCE(!state->port.xmit_buf)) {
 		uart_port_unlock(port, flags);
 		return 0;
 	}
 
-	while (port) {
-		c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
-		if (count < c)
-			c = count;
-		if (c <= 0)
-			break;
-		memcpy(circ->buf + circ->head, buf, c);
-		circ->head = (circ->head + c) & (UART_XMIT_SIZE - 1);
-		buf += c;
-		count -= c;
-		ret += c;
-	}
+	if (port)
+		ret = kfifo_in(&state->port.xmit_fifo, buf, count);
 
 	__uart_start(state);
 	uart_port_unlock(port, flags);
@@ -625,7 +610,7 @@ static unsigned int uart_write_room(struct tty_struct *tty)
 	unsigned int ret;
 
 	port = uart_port_lock(state, flags);
-	ret = uart_circ_chars_free(&state->xmit);
+	ret = kfifo_avail(&state->port.xmit_fifo);
 	uart_port_unlock(port, flags);
 	return ret;
 }
@@ -638,7 +623,7 @@ static unsigned int uart_chars_in_buffer(struct tty_struct *tty)
 	unsigned int ret;
 
 	port = uart_port_lock(state, flags);
-	ret = uart_circ_chars_pending(&state->xmit);
+	ret = kfifo_len(&state->port.xmit_fifo);
 	uart_port_unlock(port, flags);
 	return ret;
 }
@@ -661,7 +646,7 @@ static void uart_flush_buffer(struct tty_struct *tty)
 	port = uart_port_lock(state, flags);
 	if (!port)
 		return;
-	uart_circ_clear(&state->xmit);
+	kfifo_reset(&state->port.xmit_fifo);
 	if (port->ops->flush_buffer)
 		port->ops->flush_buffer(port);
 	uart_port_unlock(port, flags);
@@ -1064,7 +1049,7 @@ static int uart_get_lsr_info(struct tty_struct *tty,
 	 * interrupt happens).
 	 */
 	if (uport->x_char ||
-	    ((uart_circ_chars_pending(&state->xmit) > 0) &&
+	    (!kfifo_is_empty(&state->port.xmit_fifo) &&
 	     !uart_tx_stopped(uport)))
 		result &= ~TIOCSER_TEMT;
 
@@ -1788,8 +1773,9 @@ static void uart_tty_port_shutdown(struct tty_port *port)
 	 * Free the transmit buffer.
 	 */
 	uart_port_lock_irq(uport);
-	buf = state->xmit.buf;
-	state->xmit.buf = NULL;
+	buf = port->xmit_buf;
+	port->xmit_buf = NULL;
+	INIT_KFIFO(port->xmit_fifo);
 	uart_port_unlock_irq(uport);
 
 	free_page((unsigned long)buf);