Re: commit 5fe212364 causes division by zero with large bauds
From: Alexey Pelykh
Date: Wed Sep 11 2013 - 02:22:52 EST
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;
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%)
4800: divisor = 625 (16), real rate 4800 (0.000000%)
9600: divisor = 384 (13), real rate 9615 (0.156250%)
14400: divisor = 256 (13), real rate 14423 (0.159722%)
19200: divisor = 192 (13), real rate 19230 (0.156250%)
28800: divisor = 128 (13), real rate 28846 (0.159722%)
38400: divisor = 96 (13), real rate 38461 (0.158854%)
57600: divisor = 64 (13), real rate 57692 (0.159722%)
115200: divisor = 32 (13), real rate 115384 (0.159722%)
230400: divisor = 16 (13), real rate 230769 (0.160156%)
460800: divisor = 8 (13), real rate 461538 (0.160156%)
921600: divisor = 4 (13), real rate 923076 (0.160156%)
1000000: divisor = 3 (16), real rate 1000000 (0.000000%)
1843200: divisor = 2 (13), real rate 1846153 (0.160211%)
3000000: divisor = 1 (16), real rate 3000000 (0.000000%)
3686400: divisor = 1 (13), real rate 3692307 (0.160238%)
Thanks,
Alexey
On Tue, Sep 10, 2013 at 10:09 PM, Felipe Balbi <balbi@xxxxxx> wrote:
> Hi Alexey,
>
> your commit 5fe212364 causes division by zero with any baud rate larger
> than 3 Mbaud (IP supports up to 3686400).
>
> Maybe this patch is all we need to get it fixed ? (untested)
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 816d1a2..b50327f 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -240,8 +240,14 @@ 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 = 0;
> + int baudAbsDiff16 = 0;
> +
> + if (n13)
> + baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
> + if (n16)
> + baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
> +
> if(baudAbsDiff13 < 0)
> baudAbsDiff13 = -baudAbsDiff13;
> if(baudAbsDiff16 < 0)
>
> Another possibility would be to convert this into a lookup table (also
> untested):
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 816d1a2..942d68e 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -224,6 +224,48 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
> pdata->enable_wakeup(up->dev, enable);
> }
>
> +struct uart_omap_config {
> + unsigned int baud;
> + unsigned int oversampling;
> + unsigned int divisor;
> +};
> +
> +static struct uart_omap_config omap_port_configs[] = {
> + { .baud = 300, .oversampling = 16, .divisor = 10000, },
> + { .baud = 300, .oversampling = 16, .divisor = 10000, },
> + { .baud = 600, .oversampling = 16, .divisor = 5000, },
> + { .baud = 1200, .oversampling = 16, .divisor = 2500, },
> + { .baud = 2400, .oversampling = 16, .divisor = 1250, },
> + { .baud = 4800, .oversampling = 16, .divisor = 625, },
> + { .baud = 9600, .oversampling = 16, .divisor = 312, },
> + { .baud = 14400, .oversampling = 16, .divisor = 208, },
> + { .baud = 19200, .oversampling = 16, .divisor = 156, },
> + { .baud = 28800, .oversampling = 16, .divisor = 704, },
> + { .baud = 38400, .oversampling = 16, .divisor = 78, },
> + { .baud = 57600, .oversampling = 16, .divisor = 52, },
> + { .baud = 115200, .oversampling = 16, .divisor = 26, },
> + { .baud = 230400, .oversampling = 16, .divisor = 13, },
> + { .baud = 460800, .oversampling = 13, .divisor = 8, },
> + { .baud = 921600, .oversampling = 13, .divisor = 4, },
> + { .baud = 1843200, .oversampling = 13, .divisor = 2, },
> + { .baud = 3000000, .oversampling = 16, .divisor = 1, },
> + { .baud = 3686400, .oversampling = 13, .divisor = 1, },
> + { } /* Terminating Entry */
> +};
> +
> +static struct uart_omap_config *
> +__serial_omap_get_config(struct uart_port *port, unsigned int baud)
> +{
> + struct uart_omap_config *cfg = omap_port_configs;
> +
> + while (cfg++) {
> + if (cfg->baud == baud)
> + return cfg;
> + }
> +
> + return NULL;
> +}
> +
> /*
> * serial_omap_baud_is_mode16 - check if baud rate is MODE16X
> * @port: uart port info
> @@ -238,16 +280,12 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
> static bool
> 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));
> - if(baudAbsDiff13 < 0)
> - baudAbsDiff13 = -baudAbsDiff13;
> - if(baudAbsDiff16 < 0)
> - baudAbsDiff16 = -baudAbsDiff16;
> -
> - return (baudAbsDiff13 > baudAbsDiff16);
> + struct uart_omap_config *cfg = __serial_omap_get_config(port, baud);
> +
> + if (!cfg)
> + return -EINVAL;
> +
> + return (cfg->oversampling == 16);
> }
>
> /*
> @@ -258,13 +296,12 @@ serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
> static unsigned int
> serial_omap_get_divisor(struct uart_port *port, unsigned int baud)
> {
> - unsigned int divisor;
> + struct uart_omap_config *cfg = __serial_omap_get_config(port, baud);
>
> - if (!serial_omap_baud_is_mode16(port, baud))
> - divisor = 13;
> - else
> - divisor = 16;
> - return port->uartclk/(baud * divisor);
> + if (!cfg)
> + return -EINVAL;
> +
> + return cfg->divisor;
> }
>
> static void serial_omap_enable_ms(struct uart_port *port)
>
> --
> balbi
--
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