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, 31 insertions, 18 deletions

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 0a0f6e21d40e..8cb65f50e830 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -11,7 +11,6 @@
 #include <linux/compiler.h>
 #include <linux/console.h>
 #include <linux/interrupt.h>
-#include <linux/circ_buf.h>
 #include <linux/spinlock.h>
 #include <linux/sched.h>
 #include <linux/tty.h>
@@ -699,7 +698,6 @@ struct uart_state {
 	struct tty_port		port;
 
 	enum uart_pm_state	pm_state;
-	struct circ_buf		xmit;
 
 	atomic_t		refcount;
 	wait_queue_head_t	remove_wait;
@@ -723,12 +721,35 @@ struct uart_state {
  */
 static inline void uart_xmit_advance(struct uart_port *up, unsigned int chars)
 {
-	struct circ_buf *xmit = &up->state->xmit;
+	struct tty_port *tport = &up->state->port;
 
-	xmit->tail = (xmit->tail + chars) & (UART_XMIT_SIZE - 1);
+	kfifo_skip_count(&tport->xmit_fifo, chars);
 	up->icount.tx += chars;
 }
 
+static inline unsigned int uart_fifo_out(struct uart_port *up,
+		unsigned char *buf, unsigned int chars)
+{
+	struct tty_port *tport = &up->state->port;
+
+	chars = kfifo_out(&tport->xmit_fifo, buf, chars);
+	up->icount.tx += chars;
+
+	return chars;
+}
+
+static inline unsigned int uart_fifo_get(struct uart_port *up,
+		unsigned char *ch)
+{
+	struct tty_port *tport = &up->state->port;
+	unsigned int chars;
+
+	chars = kfifo_get(&tport->xmit_fifo, ch);
+	up->icount.tx += chars;
+
+	return chars;
+}
+
 struct module;
 struct tty_driver;
 
@@ -764,7 +785,7 @@ enum UART_TX_FLAGS {
 		       for_test, for_post)				      \
 ({									      \
 	struct uart_port *__port = (uport);				      \
-	struct circ_buf *xmit = &__port->state->xmit;			      \
+	struct tty_port *__tport = &__port->state->port;		      \
 	unsigned int pending;						      \
 									      \
 	for (; (for_test) && (tx_ready); (for_post), __port->icount.tx++) {   \
@@ -775,17 +796,18 @@ enum UART_TX_FLAGS {
 			continue;					      \
 		}							      \
 									      \
-		if (uart_circ_empty(xmit) || uart_tx_stopped(__port))	      \
+		if (uart_tx_stopped(__port))				      \
+			break;						      \
+									      \
+		if (!kfifo_get(&__tport->xmit_fifo, &(ch)))		      \
 			break;						      \
 									      \
-		(ch) = xmit->buf[xmit->tail];				      \
 		(put_char);						      \
-		xmit->tail = (xmit->tail + 1) % UART_XMIT_SIZE;		      \
 	}								      \
 									      \
 	(tx_done);							      \
 									      \
-	pending = uart_circ_chars_pending(xmit);			      \
+	pending = kfifo_len(&__tport->xmit_fifo);			      \
 	if (pending < WAKEUP_CHARS) {					      \
 		uart_write_wakeup(__port);				      \
 									      \
@@ -974,15 +996,6 @@ bool uart_match_port(const struct uart_port *port1,
 int uart_suspend_port(struct uart_driver *reg, struct uart_port *port);
 int uart_resume_port(struct uart_driver *reg, struct uart_port *port);
 
-#define uart_circ_empty(circ)		((circ)->head == (circ)->tail)
-#define uart_circ_clear(circ)		((circ)->head = (circ)->tail = 0)
-
-#define uart_circ_chars_pending(circ)	\
-	(CIRC_CNT((circ)->head, (circ)->tail, UART_XMIT_SIZE))
-
-#define uart_circ_chars_free(circ)	\
-	(CIRC_SPACE((circ)->head, (circ)->tail, UART_XMIT_SIZE))
-
 static inline int uart_tx_stopped(struct uart_port *port)
 {
 	struct tty_struct *tty = port->state->port.tty;