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, 12 insertions, 14 deletions

diff --git a/drivers/tty/serial/ip22zilog.c b/drivers/tty/serial/ip22zilog.c
index 320b29cd4683..c2cae50f06f3 100644
--- a/drivers/tty/serial/ip22zilog.c
+++ b/drivers/tty/serial/ip22zilog.c
@@ -355,7 +355,8 @@ static void ip22zilog_status_handle(struct uart_ip22zilog_port *up,
 static void ip22zilog_transmit_chars(struct uart_ip22zilog_port *up,
 				    struct zilog_channel *channel)
 {
-	struct circ_buf *xmit;
+	struct tty_port *tport;
+	unsigned char c;
 
 	if (ZS_IS_CONS(up)) {
 		unsigned char status = readb(&channel->control);
@@ -398,20 +399,18 @@ static void ip22zilog_transmit_chars(struct uart_ip22zilog_port *up,
 
 	if (up->port.state == NULL)
 		goto ack_tx_int;
-	xmit = &up->port.state->xmit;
-	if (uart_circ_empty(xmit))
-		goto ack_tx_int;
+	tport = &up->port.state->port;
 	if (uart_tx_stopped(&up->port))
 		goto ack_tx_int;
+	if (!uart_fifo_get(&up->port, &c))
+		goto ack_tx_int;
 
 	up->flags |= IP22ZILOG_FLAG_TX_ACTIVE;
-	writeb(xmit->buf[xmit->tail], &channel->data);
+	writeb(c, &channel->data);
 	ZSDELAY();
 	ZS_WSYNC(channel);
 
-	uart_xmit_advance(&up->port, 1);
-
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(&up->port);
 
 	return;
@@ -600,17 +599,16 @@ static void ip22zilog_start_tx(struct uart_port *port)
 		port->icount.tx++;
 		port->x_char = 0;
 	} else {
-		struct circ_buf *xmit = &port->state->xmit;
+		struct tty_port *tport = &port->state->port;
+		unsigned char c;
 
-		if (uart_circ_empty(xmit))
+		if (!uart_fifo_get(port, &c))
 			return;
-		writeb(xmit->buf[xmit->tail], &channel->data);
+		writeb(c, &channel->data);
 		ZSDELAY();
 		ZS_WSYNC(channel);
 
-		uart_xmit_advance(port, 1);
-
-		if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 			uart_write_wakeup(&up->port);
 	}
 }