diff options
| author | Andy Shevchenko <andriy.shevchenko@linux.intel.com> | 2015-03-13 18:51:12 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-03-26 23:00:36 +0100 |
| commit | 21947ba654a685ab48f2d4089c5c2d27443c2d0d (patch) | |
| tree | 2d1ab7e24472a8bf2754feb2283f4d976280aef4 /drivers/tty/serial | |
| parent | 49708c9e6cbb3c534677f429053bd18c2e948069 (diff) | |
| download | linux-21947ba654a685ab48f2d4089c5c2d27443c2d0d.tar.bz2 | |
serial: 8250_pci: replace switch-case by formula
This patch replaces a switch-case by a formula using rational best
approximation 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) numerator, 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)
2180 3103 16 70254592 70254592 134(32768)
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)
9893 17154 16 57671680 57671680 110(32768)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/serial')
| -rw-r--r-- | drivers/tty/serial/8250/8250_pci.c | 40 | ||||
| -rw-r--r-- | drivers/tty/serial/8250/Kconfig | 1 |
2 files changed, 10 insertions, 31 deletions
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c index 495da0643278..7e0519923eb5 100644 --- a/drivers/tty/serial/8250/8250_pci.c +++ b/drivers/tty/serial/8250/8250_pci.c @@ -21,6 +21,7 @@ #include <linux/serial_core.h> #include <linux/8250_pci.h> #include <linux/bitops.h> +#include <linux/rational.h> #include <asm/byteorder.h> #include <asm/io.h> @@ -1393,45 +1394,22 @@ byt_set_termios(struct uart_port *p, struct ktermios *termios, struct ktermios *old) { unsigned int baud = tty_termios_baud_rate(termios); - unsigned int m, n; + unsigned long fref = 100000000, fuart = baud * 16; + unsigned long w = BIT(15) - 1; + unsigned long m, n; u32 reg; + /* Get Fuart closer to Fref */ + fuart *= rounddown_pow_of_two(fref / fuart); + /* * For baud rates 0.5M, 1M, 1.5M, 2M, 2.5M, 3M, 3.5M and 4M the * dividers must be adjusted. * * uartclk = (m / n) * 100 MHz, where m <= n */ - 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; - } + rational_best_approximation(fuart, fref, w, w, &m, &n); + p->uartclk = fuart; /* Reset the clock */ reg = (m << BYT_PRV_CLK_M_VAL_SHIFT) | (n << BYT_PRV_CLK_N_VAL_SHIFT); diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig index 6f7f2d753def..c35070356528 100644 --- a/drivers/tty/serial/8250/Kconfig +++ b/drivers/tty/serial/8250/Kconfig @@ -108,6 +108,7 @@ config SERIAL_8250_PCI tristate "8250/16550 PCI device support" if EXPERT depends on SERIAL_8250 && PCI default SERIAL_8250 + select RATIONAL help This builds standard PCI serial support. You may be able to disable this feature if you only need legacy serial support. |