linux-kernel - [PATCH 4/8] serial: fsl_lpuart: handle break and make sysrq work

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Date:   Tue, 11 May 2021 22:01:44 +0200
From:   Michael Walle <michael@...le.cc>
To:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Angelo Dureghello <angelo.dureghello@...esys.com>,
        Fugang Duan <fugang.duan@....com>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        Michael Walle <michael@...le.cc>
Subject: [PATCH 4/8] serial: fsl_lpuart: handle break and make sysrq work

Although there is already (broken) sysrq characters handling, a break
condition was never detected. There is also a possible deadlock because
we might call handle_sysrq() while still holding the port lock.

Add support for break detection and use the proper
uart_unlock_and_check_sysrq() to defer calling handle_sysrq().

Signed-off-by: Michael Walle <michael@...le.cc>
---
 drivers/tty/serial/fsl_lpuart.c | 36 ++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 37e02d992c0b..0a578ad31a19 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -910,6 +910,7 @@ static void lpuart32_rxint(struct lpuart_port *sport)
 	unsigned int flg, ignored = 0;
 	struct tty_port *port = &sport->port.state->port;
 	unsigned long rx, sr;
+	bool is_break;
 
 	spin_lock(&sport->port.lock);
 
@@ -924,14 +925,27 @@ static void lpuart32_rxint(struct lpuart_port *sport)
 		rx = lpuart32_read(&sport->port, UARTDATA);
 		rx &= UARTDATA_MASK;
 
-		if (uart_handle_sysrq_char(&sport->port, rx))
+		/*
+		 * The LPUART can't distinguish between a break and a framing error,
+		 * thus we assume it is a break if the received data is zero.
+		 */
+		is_break = sr & UARTSTAT_FE && !rx;
+
+		if (is_break && uart_handle_break(&sport->port))
+			continue;
+
+		if (uart_prepare_sysrq_char(&sport->port, rx))
 			continue;
 
 		if (sr & (UARTSTAT_PE | UARTSTAT_OR | UARTSTAT_FE)) {
-			if (sr & UARTSTAT_PE)
-				sport->port.icount.parity++;
-			else if (sr & UARTSTAT_FE)
+			if (sr & UARTSTAT_PE) {
+				if (is_break)
+					sport->port.icount.brk++;
+				else
+					sport->port.icount.parity++;
+			} else if (sr & UARTSTAT_FE) {
 				sport->port.icount.frame++;
+			}
 
 			if (sr & UARTSTAT_OR)
 				sport->port.icount.overrun++;
@@ -944,22 +958,24 @@ static void lpuart32_rxint(struct lpuart_port *sport)
 
 			sr &= sport->port.read_status_mask;
 
-			if (sr & UARTSTAT_PE)
-				flg = TTY_PARITY;
-			else if (sr & UARTSTAT_FE)
+			if (sr & UARTSTAT_PE) {
+				if (is_break)
+					flg = TTY_BREAK;
+				else
+					flg = TTY_PARITY;
+			} else if (sr & UARTSTAT_FE) {
 				flg = TTY_FRAME;
+			}
 
 			if (sr & UARTSTAT_OR)
 				flg = TTY_OVERRUN;
-
-			sport->port.sysrq = 0;
 		}
 
 		tty_insert_flip_char(port, rx, flg);
 	}
 
 out:
-	spin_unlock(&sport->port.lock);
+	uart_unlock_and_check_sysrq(&sport->port);
 
 	tty_flip_buffer_push(port);
 }
-- 
2.20.1