On Wed, Mar 11, 2015 at 10:19:17PM +0200, Andy Shevchenko wrote:
> This patch replaces a case switch by a serial8250_get_ps() call that does
> necessary calculations for byt_set_termios().
>
> Below is a list of the calculations done for all defined baud rates. Each line
> in a format: 1) nominator, 2) denominator, 3) prescaler, 4) Fuart, 5) port UART
> clock, 6) list of baud rates with DLAB values.
>
> 4 5 16 80000000 80000000 2500000(2)
> 14 25 16 56000000 56000000 3500000(1)
> 16 25 16 64000000 64000000 500000(8),1000000(4),2000000(2),4000000(1)
> 24 25 16 96000000 96000000 1500000(4),3000000(2)
> 2304 3125 16 73728000 73728000 576000(8),1152000(4)
> 8192 15625 16 52428800 52428800 50(65536),200(16384)
> 9216 15625 16 58982400 58982400 1800(2048),57600(64),115200(32),230400(16),460800(8),921600(4),1843200(2)
> 12288 15625 16 78643200 78643200 75(65536),150(32768),300(16384),600(8192),1200(4096),2400(2048),4800(1024),9600(512),19200(256),38400(128)
> 11264 19531 16 57672418 57671680 110(32768)
> 17152 24414 16 70254771 70254592 134(32768)
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_pci.c | 36 ++++++------------------------------
> 1 file changed, 6 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
> index 11784e9..544d11b 100644
> --- a/drivers/tty/serial/8250/8250_pci.c
> +++ b/drivers/tty/serial/8250/8250_pci.c
> @@ -1401,37 +1401,13 @@ byt_set_termios(struct uart_port *p, struct ktermios *termios,
> * dividers must be adjusted.
> *
> * uartclk = (m / n) * 100 MHz, where m <= n
> + *
> + * For now we ignore a prescaler value since it will be always 16 for
> + * standard baud rates.
> + *
> + * Note, that the formula will not work for rates less than 110 baud.
> */
> - switch (baud) {
> - case 500000:
> - case 1000000:
> - case 2000000:
> - case 4000000:
> - m = 64;
> - n = 100;
> - p->uartclk = 64000000;
> - break;
> - case 3500000:
> - m = 56;
> - n = 100;
> - p->uartclk = 56000000;
> - break;
> - case 1500000:
> - case 3000000:
> - m = 48;
> - n = 100;
> - p->uartclk = 48000000;
> - break;
> - case 2500000:
> - m = 40;
> - n = 100;
> - p->uartclk = 40000000;
> - break;
> - default:
> - m = 2304;
> - n = 3125;
> - p->uartclk = 73728000;
> - }
> + serial8250_get_ps(p, baud, 100000000, 15, &m, &n);
The UART on BYT does not have prescaler like Intel MID UARTs do.
Shouldn't you just calculate the m and n values for the fractional
divider in that function, it is the shared part, and leave the
calculation of the prescaler value as Intel MID specific thing for
now?
Thanks,
--
heikki
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