Re: commit 5fe212364 causes division by zero with large bauds
From: Felipe Balbi <hidden>
Date: 2013-09-11 18:39:45
Also in:
linux-omap, lkml
Hi, On Wed, Sep 11, 2013 at 09:22:26AM +0300, Alexey Pelykh wrote:
quoted hunk ↗ jump to hunk
Hi Felipe, Thanks for finding this issue. Indeed, there is a bug on 3M+ baud rates. First patch is close to a complete fix, but still contains div-by-zero issue. Here is my version:diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c index 816d1a2..808a880 100644 --- a/drivers/tty/serial/omap-serial.c +++ b/drivers/tty/serial/omap-serial.c@@ -240,8 +240,8 @@ serial_omap_baud_is_mode16(struct uart_port *port,unsigned int baud) { unsigned int n13 = port->uartclk / (13 * baud); unsigned int n16 = port->uartclk / (16 * baud); - int baudAbsDiff13 = baud - (port->uartclk / (13 * n13)); - int baudAbsDiff16 = baud - (port->uartclk / (16 * n16)); + int baudAbsDiff13 = n13 ? (baud - (port->uartclk / (13 * n13))) : INT_MAX; + int baudAbsDiff16 = n16 ? (baud - (port->uartclk / (16 * n16))) : INT_MAX;
IOW: int baudAbsDiff13 = 0; if (n13) baudAbsDiff13 = (baud - (port->uartclk / (13 * n13))); which is exactly what my patch did. I fail to see where division by zero would be coming from.
if(baudAbsDiff13 < 0)
baudAbsDiff13 = -baudAbsDiff13;
if(baudAbsDiff16 < 0)
With 48MHz UART clock, it will give
300: divisor = 12307 (13), real rate 300 (0.000000%)
600: divisor = 6153 (13), real rate 600 (0.000000%)
1200: divisor = 3076 (13), real rate 1200 (0.000000%)
2400: divisor = 1538 (13), real rate 2400 (0.000000%)TRM has these all set with oversampling of 16. In fact only 460800, 921600, 1843200 and 3686400 should be using oversampling of 13. -- balbi
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