When userspace opens the console, we call set_termios() passing a termios with the console's configured baud rate. Currently this causes dw8250_set_termios() to disable and then re-enable the UART clock at the same frequency as it was originally. This can cause corruption of any concurrent console output. Fix it by skipping the reclocking if we are already at the correct rate.

Signed-off-by: Peter Collingbourne pcc@google.com Link: https://linux-review.googlesource.com/id/I2e3761d239cbf29ed41412e5338f30bffe... Fixes: 4e26b134bd17 ("serial: 8250_dw: clock rate handling for all ACPI platforms") Cc: stable@vger.kernel.org --- drivers/tty/serial/8250/8250_dw.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index 2d1f350a4bea..c1d43f040c43 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -357,9 +357,9 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios, long rate; int ret;

- clk_disable_unprepare(d->clk); rate = clk_round_rate(d->clk, newrate); - if (rate > 0) { + if (rate > 0 && p->uartclk != rate) { + clk_disable_unprepare(d->clk); /* * Note that any clock-notifer worker will block in * serial8250_update_uartclk() until we are done. @@ -367,8 +367,8 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios, ret = clk_set_rate(d->clk, newrate); if (!ret) p->uartclk = rate; + clk_prepare_enable(d->clk); } - clk_prepare_enable(d->clk);

dw8250_do_set_termios(p, termios, old); }