[PATCH 6.6 227/396] serial: 8250_dw: Do not reclock if already at correct rate

Greg Kroah-Hartman
2024-04-01T16:47:13Z

From: Peter Collingbourne <pcc@google.com>

commit e5d6bd25f93d6ae158bb4cd04956cb497a85b8ef upstream.

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>
Fixes: 4e26b134bd17 ("serial: 8250_dw: clock rate handling for all ACPI platforms")
Cc: stable@vger.kernel.org
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240222192635.1050502-1-pcc@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/serial/8250/8250_dw.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- 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 ua
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 ua
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);
}