[PATCH] tty/8250_early: Prevent rounding error in uartclk to baud ratio
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STALE5132d
From: Alexey Brodkin <hidden>
Date: 2012-09-28 12:12:38
Also in:
lkml
Subsystem:
8250/16?50 (and clone uarts) serial driver, the rest, tty layer and serial drivers · Maintainers:
Greg Kroah-Hartman, Linus Torvalds, Jiri Slaby
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 <abrodkin@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); c = serial_in(port, UART_LCR); serial_out(port, UART_LCR, c | UART_LCR_DLAB); serial_out(port, UART_DLL, divisor & 0xff);
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1.7.9.5