On 09/28/2012 02:03 PM, Alexey Brodkin wrote: > Modify divisor to select the nearest baud rate divider rather than the > lowest. It minimizes baud rate errors especially on low UART clock > frequencies. > > For example, if uartclk is 33000000 and baud is 115200 the ratio is > about 17.9 The current code selects 17 (5% error) but should select 18 > (0.5% error). > > On the same lines as following: > http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.9-rc3/2.6.9-rc3-mm2/broken-out/serial-pick-nearest-baud-rate-divider.patch > > Signed-off-by: Alexey Brodkin <abrod...@synopsys.com> > --- > drivers/tty/serial/8250_early.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/8250_early.c b/drivers/tty/serial/8250_early.c > index eaafb98..cfc46b7 100644 > --- a/drivers/tty/serial/8250_early.c > +++ b/drivers/tty/serial/8250_early.c > @@ -140,7 +140,7 @@ static void __init init_port(struct > early_serial8250_device *device) > serial_out(port, UART_FCR, 0); /* no fifo */ > serial_out(port, UART_MCR, 0x3); /* DTR + RTS */ > > - divisor = port->uartclk / (16 * device->baud); > + divisor = (port->uartclk + (8 * device->baud)) / (16 * device->baud);
So this should be in fact DIV_ROUND_CLOSEST(), right? But anyway I'm missing any explanation of *why* this is needed? This should be part of the commit log. Is there any bug you are fixing here? thanks, -- js suse labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
