linux-kernel - [PATCH] serial: meson+qcom: don't advance the kfifo twice

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Date: Tue, 16 Apr 2024 07:48:25 +0200
From: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
To: gregkh@...uxfoundation.org
Cc: linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Jiri Slaby (SUSE)" <jirislaby@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Kevin Hilman <khilman@...libre.com>,
	Jerome Brunet <jbrunet@...libre.com>,
	Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-amlogic@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org
Subject: [PATCH] serial: meson+qcom: don't advance the kfifo twice

Marek reports, that the -next commit 1788cf6a91d9 (tty: serial: switch
from circ_buf to kfifo) broke meson_uart and qcom_geni_serial. The
commit mistakenly advanced the kfifo twice: once by
uart_fifo_get()/kfifo_out() and second time by uart_xmit_advance().

To advance the fifo only once, drop the superfluous uart_xmit_advance()
from both.

To count the TX statistics properly, use uart_fifo_out() in
qcom_geni_serial (meson_uart_start_tx() already uses that).

I checked all other uses of uart_xmit_advance() and they appear correct:
either they are finishing DMA transfers or are after peek/linear_ptr
(i.e. they do not advance fifo).

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Neil Armstrong <neil.armstrong@...aro.org>
Cc: Kevin Hilman <khilman@...libre.com>
Cc: Jerome Brunet <jbrunet@...libre.com>
Cc: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
---
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-amlogic@...ts.infradead.org
Cc: linux-arm-msm@...r.kernel.org
---
 drivers/tty/serial/meson_uart.c       | 1 -
 drivers/tty/serial/qcom_geni_serial.c | 4 +---
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 4587ed4d4d5d..8eb586ac3b0d 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -162,7 +162,6 @@ static void meson_uart_start_tx(struct uart_port *port)
 			break;
 
 		writel(ch, port->membase + AML_UART_WFIFO);
-		uart_xmit_advance(port, 1);
 	}
 
 	if (!kfifo_is_empty(&tport->xmit_fifo)) {
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 7814982f1921..2bd25afe0d92 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -855,7 +855,6 @@ static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
 					     unsigned int chunk)
 {
 	struct qcom_geni_serial_port *port = to_dev_port(uport);
-	struct tty_port *tport = &uport->state->port;
 	unsigned int tx_bytes, remaining = chunk;
 	u8 buf[BYTES_PER_FIFO_WORD];
 
@@ -863,8 +862,7 @@ static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
 		memset(buf, 0, sizeof(buf));
 		tx_bytes = min(remaining, BYTES_PER_FIFO_WORD);
 
-		tx_bytes = kfifo_out(&tport->xmit_fifo, buf, tx_bytes);
-		uart_xmit_advance(uport, tx_bytes);
+		tx_bytes = uart_fifo_out(uport, buf, tx_bytes);
 
 		iowrite32_rep(uport->membase + SE_GENI_TX_FIFOn, buf, 1);
 
-- 
2.44.0