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) <[email protected]>
Cc: Al Cooper <[email protected]>
Cc: Matthias Brugger <[email protected]>
Cc: AngeloGioacchino Del Regno <[email protected]>
Cc: Kumaravel Thiagarajan <[email protected]>
Cc: Tharun Kumar P <[email protected]>
Cc: Russell King <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: Richard Genoud <[email protected]>
Cc: Nicolas Ferre <[email protected]>
Cc: Alexandre Belloni <[email protected]>
Cc: Claudiu Beznea <[email protected]>
Cc: Alexander Shiyan <[email protected]>
Cc: Baruch Siach <[email protected]>
Cc: Maciej W. Rozycki <[email protected]>
Cc: Shawn Guo <[email protected]>
Cc: Sascha Hauer <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: Neil Armstrong <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: Jerome Brunet <[email protected]>
Cc: Martin Blumenstingl <[email protected]>
Cc: Taichi Sugaya <[email protected]>
Cc: Takao Orito <[email protected]>
Cc: Bjorn Andersson <[email protected]>
Cc: Konrad Dybcio <[email protected]>
Cc: Pali Rohár <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Naveen N. Rao <[email protected]>
Cc: Manivannan Sadhasivam <[email protected]>
Cc: Krzysztof Kozlowski <[email protected]>
Cc: Alim Akhtar <[email protected]>
Cc: Laxman Dewangan <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Jonathan Hunter <[email protected]>
Cc: Orson Zhai <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Chunyan Zhang <[email protected]>
Cc: Patrice Chotard <[email protected]>
Cc: Maxime Coquelin <[email protected]>
Cc: Alexandre Torgue <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Hammer Hsieh <[email protected]>
Cc: Peter Korsgaard <[email protected]>
Cc: Timur Tabi <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: Christian König <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

1 files changed, 10 insertions, 6 deletions

diff --git a/drivers/tty/serial/sccnxp.c b/drivers/tty/serial/sccnxp.c
index f24217a560d7..6d1d142fd216 100644
--- a/drivers/tty/serial/sccnxp.c
+++ b/drivers/tty/serial/sccnxp.c
@@ -439,7 +439,7 @@ static void sccnxp_handle_rx(struct uart_port *port)
 static void sccnxp_handle_tx(struct uart_port *port)
 {
 	u8 sr;
-	struct circ_buf *xmit = &port->state->xmit;
+	struct tty_port *tport = &port->state->port;
 	struct sccnxp_port *s = dev_get_drvdata(port->dev);
 
 	if (unlikely(port->x_char)) {
@@ -449,7 +449,7 @@ static void sccnxp_handle_tx(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)) {
 		/* Disable TX if FIFO is empty */
 		if (sccnxp_port_read(port, SCCNXP_SR_REG) & SR_TXEMT) {
 			sccnxp_disable_irq(port, IMR_TXRDY);
@@ -461,16 +461,20 @@ static void sccnxp_handle_tx(struct uart_port *port)
 		return;
 	}
 
-	while (!uart_circ_empty(xmit)) {
+	while (1) {
+		unsigned char ch;
+
 		sr = sccnxp_port_read(port, SCCNXP_SR_REG);
 		if (!(sr & SR_TXRDY))
 			break;
 
-		sccnxp_port_write(port, SCCNXP_THR_REG, xmit->buf[xmit->tail]);
-		uart_xmit_advance(port, 1);
+		if (!uart_fifo_get(port, &ch))
+			break;
+
+		sccnxp_port_write(port, SCCNXP_THR_REG, ch);
 	}
 
-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+	if (kfifo_len(&tport->xmit_fifo) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
 }