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@xxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_pci.c | 36 +++++-------------------------------
drivers/tty/serial/8250/Kconfig | 1 +
2 files changed, 6 insertions(+), 31 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 11784e9..9bb2eec 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>
@@ -1393,7 +1394,8 @@ 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 w = BIT(15) - 1;
+ unsigned long m, n;
u32 reg;
/*
@@ -1402,36 +1404,8 @@ byt_set_termios(struct uart_port *p, struct ktermios *termios,
*
* 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;
- }
+ p->uartclk = baud * 16;
+ rational_best_approximation(p->uartclk, 100000000, w, w, &m, &n);
/* 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 6f7f2d7..c350703 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.
--
2.1.4
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