[PATCH] serial: imx: Restore original RXTL for console to fix data loss

[Fabio Estevam]

Commit 7a637784d517 ("serial: imx: reduce RX interrupt frequency")
introduced a regression on the i.MX6UL EVK board. The issue can be
reproduced with the following steps:

- Open vi on the board.
- Paste a text file (~150 characters).
- Save the file, then repeat the process.
- Compare the sha256sum of the saved files.

The checksums do not match due to missing characters or entire lines.

Fix this by restoring the RXTL value to 1 when the UART is used as a
console.

This ensures timely RX interrupts and reliable data reception in console
mode.

With this change, pasted content is saved correctly, and checksums are
always consistent.

Cc: stable at vger.kernel.org
Fixes: 7a637784d517 ("serial: imx: reduce RX interrupt frequency")
Signed-off-by: Fabio Estevam <festevam at gmail.com>
---
 drivers/tty/serial/imx.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index bd02ee898f5d..500dfc009d03 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -235,6 +235,7 @@ struct imx_port {
 	enum imx_tx_state	tx_state;
 	struct hrtimer		trigger_start_tx;
 	struct hrtimer		trigger_stop_tx;
+	unsigned int		rxtl;
 };
 
 struct imx_port_ucrs {
@@ -1339,6 +1340,7 @@ static void imx_uart_clear_rx_errors(struct imx_port *sport)
 
 #define TXTL_DEFAULT 8
 #define RXTL_DEFAULT 8 /* 8 characters or aging timer */
+#define RXTL_CONSOLE_DEFAULT 1
 #define TXTL_DMA 8 /* DMA burst setting */
 #define RXTL_DMA 9 /* DMA burst setting */
 
@@ -1457,7 +1459,7 @@ static void imx_uart_disable_dma(struct imx_port *sport)
 	ucr1 &= ~(UCR1_RXDMAEN | UCR1_TXDMAEN | UCR1_ATDMAEN);
 	imx_uart_writel(sport, ucr1, UCR1);
 
-	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);
 
 	sport->dma_is_enabled = 0;
 }
@@ -1482,7 +1484,12 @@ static int imx_uart_startup(struct uart_port *port)
 		return retval;
 	}
 
-	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+	if (uart_console(&sport->port))
+		sport->rxtl = RXTL_CONSOLE_DEFAULT;
+	else
+		sport->rxtl = RXTL_DEFAULT;
+
+	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);
 
 	/* disable the DREN bit (Data Ready interrupt enable) before
 	 * requesting IRQs
@@ -1948,7 +1955,7 @@ static int imx_uart_poll_init(struct uart_port *port)
 	if (retval)
 		clk_disable_unprepare(sport->clk_ipg);
 
-	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);
 
 	uart_port_lock_irqsave(&sport->port, &flags);
 
@@ -2040,7 +2047,7 @@ static int imx_uart_rs485_config(struct uart_port *port, struct ktermios *termio
 		/* If the receiver trigger is 0, set it to a default value */
 		ufcr = imx_uart_readl(sport, UFCR);
 		if ((ufcr & UFCR_RXTL_MASK) == 0)
-			imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+			imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);
 		imx_uart_start_rx(port);
 	}
 
@@ -2302,7 +2309,7 @@ imx_uart_console_setup(struct console *co, char *options)
 	else
 		imx_uart_console_get_options(sport, &baud, &parity, &bits);
 
-	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, RXTL_DEFAULT);
+	imx_uart_setup_ufcr(sport, TXTL_DEFAULT, sport->rxtl);
 
 	retval = uart_set_options(&sport->port, co, baud, parity, bits, flow);
 
-- 
2.34.1