From 24d481ecae1614cf02e638c8dce9b6e8bf230603 Mon Sep 17 00:00:00 2001 From: Anton Vorontsov Date: Sat, 19 Sep 2009 13:13:20 -0700 Subject: [PATCH] 8250: Now honours baud rate lower bounds A platform clock drives 8250 ports in most SOC systems, the clock might run at high frequencies, and so it's not always possible to downscale uart clock to a desired value. Currently the 8250 uart driver accepts not supported baud rates, and what is worse, it is doing this silently, and then passes not accepted values to a new termios, so userspace has no chance to catch this kind of errors (userspace verifies that settings were accepted by reading back and comparing the settings). This patch fixes the issue by passing minimum baud rate to the uart_get_baud_rate() call, the call should take care of all bounds, so userspace should now report: # stty -F /dev/ttyS0 speed 300 115200 stty: /dev/ttyS0: unable to perform all requested operations p.s. uart_get_baud_rate() falls back to 9600, which still might be too low for some 10 GHz platforms, but that's a separate issue, and we can wait with fixing this till we find such a platform. Signed-off-by: Anton Vorontsov Signed-off-by: Alan Cox Signed-off-by: Greg Kroah-Hartman --- drivers/serial/8250.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 83168a6..1fd4894 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -2272,7 +2272,9 @@ serial8250_set_termios(struct uart_port *port, struct ktermios *termios, /* * Ask the core to calculate the divisor for us. */ - baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16); + baud = uart_get_baud_rate(port, termios, old, + port->uartclk / 16 / 0xffff, + port->uartclk / 16); quot = serial8250_get_divisor(port, baud); /* -- 2.7.4