linux-kernel - [PATCH 5/6] tty: serial: fsl_lpuart: set RTS watermark for lpuart

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Message-Id: <20230130064449.9564-6-sherry.sun@nxp.com>
Date:   Mon, 30 Jan 2023 14:44:48 +0800
From:   Sherry Sun <sherry.sun@....com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: [PATCH 5/6] tty: serial: fsl_lpuart: set RTS watermark for lpuart

Add RTS watermark support for LPUART. The RX RTS_B output negates when
the number of empty words in the receive FIFO is greater or equal to
RTSWATER. Here set the RTSWATER to half of the rxfifo_size.

Signed-off-by: Sherry Sun <sherry.sun@....com>
---
 drivers/tty/serial/fsl_lpuart.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 2789749d3d0d..c35e49a09bcc 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -201,6 +201,7 @@
 #define UARTDATA_MASK		0x3ff
 
 #define UARTMODIR_IREN		0x00020000
+#define UARTMODIR_RTSWATER	GENMASK(10, 8)
 #define UARTMODIR_TXCTSSRC	0x00000020
 #define UARTMODIR_TXCTSC	0x00000010
 #define UARTMODIR_RXRTSE	0x00000008
@@ -1573,6 +1574,13 @@ static void lpuart32_setup_watermark(struct lpuart_port *sport)
 	      (0x0 << UARTWATER_TXWATER_OFF);
 	lpuart32_write(&sport->port, val, UARTWATER);
 
+	/* set RTS watermark */
+	if (!uart_console(&sport->port)) {
+		val = lpuart32_read(&sport->port, UARTMODIR);
+		val |= FIELD_PREP(UARTMODIR_RTSWATER, sport->rxfifo_size >> 1);
+		lpuart32_write(&sport->port, val, UARTMODIR);
+	}
+
 	/* Restore cr2 */
 	lpuart32_write(&sport->port, ctrl_saved, UARTCTRL);
 }
-- 
2.17.1