Commit 74365bc1 authored by Johan Hovold's avatar Johan Hovold Committed by Greg Kroah-Hartman
Browse files

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
divisors.

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.

Tested-by: default avatarSerge Semin <fancer.lancer@gmail.com>
Reviewed-by: default avatarSerge Semin <fancer.lancer@gmail.com>
Acked-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211015111422.1027-4-johan@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d2248ca8

drivers/tty/serial/8250/8250_dw.c

+4 −7
Original line number Diff line number Diff line
@@ -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) {

		/*

		 * Preliminary 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;

	}

	clk_prepare_enable(d->clk);