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Date:   Fri, 15 Oct 2021 13:14:22 +0200
From:   Johan Hovold <>
To:     Greg Kroah-Hartman <>
Cc:     Jiri Slaby <>,
        Andy Shevchenko <>,
        Serge Semin <>,,,
        Johan Hovold <>
Subject: [PATCH 3/3] serial: 8250_dw: drop bogus uartclk optimisation

The driver was updating the port uartclk before setting the new rate in
an attempt to avoid having the clock notifier redundantly update the

The set_termios() callback is however called under the termios semaphore
and tty-port mutex so the worker scheduled by the clock notifier will
block in serial8250_update_uartclk() until the uartclk and divisors have
been updated anyway.

Drop the unnecessary swaps and incorrect comment and simply update the
uartclk field if the clock-rate change was successful.

Signed-off-by: Johan Hovold <>
 drivers/tty/serial/8250/8250_dw.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index a3a0154da567..52e03dd0eb3b 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -338,15 +338,12 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
 	rate = clk_round_rate(d->clk, newrate);
 	if (rate > 0) {
-		 * Premilinary set the uartclk to the new clock rate so the
-		 * clock update event handler caused by the clk_set_rate()
-		 * calling wouldn't actually update the UART divisor since
-		 * we about to do this anyway.
+		 * Note that any clock-notifer worker will block in
+		 * serial8250_update_uartclk() until we are done.
-		swap(p->uartclk, rate);
 		ret = clk_set_rate(d->clk, newrate);
-		if (ret)
-			swap(p->uartclk, rate);
+		if (!ret)
+			p->uartclk = rate;

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