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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.19 0899/1157] serial: 8250: Create serial_lsr_in()
Date:   Mon, 15 Aug 2022 20:04:15 +0200
Message-Id: <20220815180515.413383265@linuxfoundation.org>
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From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

[ Upstream commit bdb70c424df1543bc02ee2639aecebd20318c599 ]

LSR register readers need to be careful in order to not lose bits that
are not preserved across reads. Create a helper that takes care of
storing the non-preserved bits into lsr_save_flags.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220608095431.18376-3-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/8250/8250.h      | 20 ++++++++++++++++++++
 drivers/tty/serial/8250/8250_core.c |  3 +--
 drivers/tty/serial/8250/8250_port.c | 15 ++++-----------
 3 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 696030cfcb09..c89cb881d9b0 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -123,6 +123,26 @@ static inline void serial_out(struct uart_8250_port *up, int offset, int value)
 	up->port.serial_out(&up->port, offset, value);
 }
 
+/**
+ *	serial_lsr_in - Read LSR register and preserve flags across reads
+ *	@up:	uart 8250 port
+ *
+ *	Read LSR register and handle saving non-preserved flags across reads.
+ *	The flags that are not preserved across reads are stored into
+ *	up->lsr_saved_flags.
+ *
+ *	Returns LSR value or'ed with the preserved flags (if any).
+ */
+static inline unsigned int serial_lsr_in(struct uart_8250_port *up)
+{
+	unsigned int lsr = up->lsr_saved_flags;
+
+	lsr |= serial_in(up, UART_LSR);
+	up->lsr_saved_flags = lsr & LSR_SAVE_FLAGS;
+
+	return lsr;
+}
+
 /*
  * For the 16C950
  */
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 3f56dbc9432b..82726cda6066 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -277,8 +277,7 @@ static void serial8250_backup_timeout(struct timer_list *t)
 	 * the "Diva" UART used on the management processor on many HP
 	 * ia64 and parisc boxes.
 	 */
-	lsr = serial_in(up, UART_LSR);
-	up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+	lsr = serial_lsr_in(up);
 	if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
 	    (!uart_circ_empty(&up->port.state->xmit) || up->port.x_char) &&
 	    (lsr & UART_LSR_THRE)) {
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3c36a06a20b0..c9d8c0de56e5 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1514,11 +1514,9 @@ static inline void __stop_tx(struct uart_8250_port *p)
 	struct uart_8250_em485 *em485 = p->em485;
 
 	if (em485) {
-		unsigned char lsr = serial_in(p, UART_LSR);
+		unsigned char lsr = serial_lsr_in(p);
 		u64 stop_delay = 0;
 
-		p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
-
 		if (!(lsr & UART_LSR_THRE))
 			return;
 		/*
@@ -1573,10 +1571,8 @@ static inline void __start_tx(struct uart_port *port)
 
 	if (serial8250_set_THRI(up)) {
 		if (up->bugs & UART_BUG_TXEN) {
-			unsigned char lsr;
+			unsigned char lsr = serial_lsr_in(up);
 
-			lsr = serial_in(up, UART_LSR);
-			up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
 			if (lsr & UART_LSR_THRE)
 				serial8250_tx_chars(up);
 		}
@@ -2007,8 +2003,7 @@ static unsigned int serial8250_tx_empty(struct uart_port *port)
 	serial8250_rpm_get(up);
 
 	spin_lock_irqsave(&port->lock, flags);
-	lsr = serial_port_in(port, UART_LSR);
-	up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+	lsr = serial_lsr_in(up);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	serial8250_rpm_put(up);
@@ -2084,9 +2079,7 @@ static void wait_for_lsr(struct uart_8250_port *up, int bits)
 
 	/* Wait up to 10ms for the character(s) to be sent. */
 	for (;;) {
-		status = serial_in(up, UART_LSR);
-
-		up->lsr_saved_flags |= status & LSR_SAVE_FLAGS;
+		status = serial_lsr_in(up);
 
 		if ((status & bits) == bits)
 			break;
-- 
2.35.1