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serial: 8250_dw: drop bogus uartclk optimisation

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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: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211015111422.1027-4-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold 2021-10-15 13:14:22 +02:00 committed by Greg Kroah-Hartman
parent d2248ca8d6
commit 74365bc138
1 changed files with 4 additions and 7 deletions
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11
drivers/tty/serial/8250/8250_dw.c
View file

@ -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);