use UDIVSLOT register on 2412, to get better accuracy when computing the
baudrate.
The clock generation is divised on 16 slots.
UDIVSLOT : if the bit n is set to 1, then for the slot n the clock generator
divide clock source by (UBRDIV + 2) instead of (UBRDIV + 1).
So if m is the number of bit set to one, the baudrate is
CLOCK / (m*(UBRDIV + 2) + (16-m)*(UBRDIV + 1))
CLOCK / (16*(UBRDIV + 1) + m)
See 2412 datasheet for more info.
Signed-off-by: Matthieu Castet <matthieu.castet@xxxxxxxxxx>
Index: linux-2.6/drivers/serial/s3c2410.c
===================================================================
--- linux-2.6.orig/drivers/serial/s3c2410.c 2008-01-02 16:24:20.000000000 +0100
+++ linux-2.6/drivers/serial/s3c2410.c 2008-01-02 18:43:38.000000000 +0100
@@ -625,6 +625,7 @@
struct s3c24xx_uart_clksrc *clksrc;
unsigned int calc;
unsigned int quot;
+ unsigned int slot;
struct clk *src;
};
@@ -643,8 +644,21 @@
rate /= clksrc->divisor;
calc->clksrc = clksrc;
- calc->quot = (rate + (8 * baud)) / (16 * baud);
- calc->calc = (rate / (calc->quot * 16));
+ if (port->type == PORT_S3C2412) {
+ unsigned long divisor;
+ unsigned long rem;
+ divisor = (rate + baud / 2) / baud;
+ calc->quot = divisor / 16; /* interger part */
+ rem = divisor % 16; /* remaining part */
+ /* slot contains rem bit(s) set to 1 */
+ calc->slot = (0xffff << (16 - rem)) & 0xffff;
+
+ calc->calc = rate / divisor;
+ }
+ else {
+ calc->quot = (rate + (8 * baud)) / (16 * baud);
+ calc->calc = (rate / (calc->quot * 16));
+ }
calc->quot--;
return 1;
@@ -652,7 +666,7 @@
static unsigned int s3c24xx_serial_getclk(struct uart_port *port,
struct s3c24xx_uart_clksrc **clksrc,
- struct clk **clk,
+ struct clk **clk, unsigned int *slot,
unsigned int baud)
{
struct s3c2410_uartcfg *cfg = s3c24xx_port_to_cfg(port);
@@ -733,6 +747,7 @@
*clksrc = best->clksrc;
*clk = best->src;
+ *slot = best->slot;
return best->quot;
}
@@ -746,7 +761,7 @@
struct s3c24xx_uart_clksrc *clksrc = NULL;
struct clk *clk = NULL;
unsigned long flags;
- unsigned int baud, quot;
+ unsigned int baud, quot, slot = 0;
unsigned int ulcon;
unsigned int umcon;
@@ -765,7 +780,7 @@
if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST)
quot = port->custom_divisor;
else
- quot = s3c24xx_serial_getclk(port, &clksrc, &clk, baud);
+ quot = s3c24xx_serial_getclk(port, &clksrc, &clk, &slot, baud);
/* check to see if we need to change clock source */
@@ -826,6 +841,8 @@
wr_regl(port, S3C2410_ULCON, ulcon);
wr_regl(port, S3C2410_UBRDIV, quot);
+ if (port->type == PORT_S3C2412)
+ wr_regl(port, S3C2412_UDIVSLOT, slot);
wr_regl(port, S3C2410_UMCON, umcon);
dbg("uart: ulcon = 0x%08x, ucon = 0x%08x, ufcon = 0x%08x\n",
Index: linux-2.6/include/asm-arm/plat-s3c/regs-serial.h
===================================================================
--- linux-2.6.orig/include/asm-arm/plat-s3c/regs-serial.h 2008-01-02 16:44:26.000000000 +0100
+++ linux-2.6/include/asm-arm/plat-s3c/regs-serial.h 2008-01-02 16:50:57.000000000 +0100
@@ -49,6 +49,7 @@
#define S3C2410_UFCON (0x08)
#define S3C2410_UMCON (0x0C)
#define S3C2410_UBRDIV (0x28)
+#define S3C2412_UDIVSLOT (0x2C)
#define S3C2410_UTRSTAT (0x10)
#define S3C2410_UERSTAT (0x14)
#define S3C2410_UFSTAT (0x18)
