[ARM] S3C: Add UDIVSLOT support for newer UARTS

Add support for the UDIVSLOT register on the newer UART blocks
which gives the capability of 1/16ths adjustment to the baud rate.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>

3 files changed, 63 insertions, 3 deletions

diff --git a/drivers/serial/s3c6400.c b/drivers/serial/s3c6400.c
index 06936d13393f..3e3785233682 100644
--- a/drivers/serial/s3c6400.c
+++ b/drivers/serial/s3c6400.c
@@ -102,6 +102,7 @@ static struct s3c24xx_uart_info s3c6400_uart_inf = {
         .name           = "Samsung S3C6400 UART",
         .type           = PORT_S3C6400,
         .fifosize       = 64,
+        .has_divslot    = 1,
         .rx_fifomask    = S3C2440_UFSTAT_RXMASK,
         .rx_fifoshift   = S3C2440_UFSTAT_RXSHIFT,
         .rx_fifofull    = S3C2440_UFSTAT_RXFULL,
diff --git a/drivers/serial/samsung.c b/drivers/serial/samsung.c
index e06686ae858b..93b5d75db126 100644
--- a/drivers/serial/samsung.c
+++ b/drivers/serial/samsung.c
@@ -508,6 +508,7 @@ s3c24xx_serial_setsource(struct uart_port *port, struct s3c24xx_uart_clksrc *c)
 struct baud_calc {
         struct s3c24xx_uart_clksrc      *clksrc;
         unsigned int                     calc;
+        unsigned int                     divslot;
         unsigned int                     quot;
         struct clk                      *src;
 };
@@ -517,6 +518,7 @@ static int s3c24xx_serial_calcbaud(struct baud_calc *calc,
                                    struct s3c24xx_uart_clksrc *clksrc,
                                    unsigned int baud)
 {
+        struct s3c24xx_uart_port *ourport = to_ourport(port);
         unsigned long rate;
 
         calc->src = clk_get(port->dev, clksrc->name);
@@ -527,8 +529,24 @@ static int s3c24xx_serial_calcbaud(struct baud_calc *calc,
         rate /= clksrc->divisor;
 
         calc->clksrc = clksrc;
-        calc->quot = (rate + (8 * baud)) / (16 * baud);
-        calc->calc = (rate / (calc->quot * 16));
+
+        if (ourport->info->has_divslot) {
+                unsigned long div = rate / baud;
+
+                /* The UDIVSLOT register on the newer UARTs allows us to
+                 * get a divisor adjustment of 1/16th on the baud clock.
+                 *
+                 * We don't keep the UDIVSLOT value (the 16ths we calculated
+                 * by not multiplying the baud by 16) as it is easy enough
+                 * to recalculate.
+                 */
+
+                calc->quot = div / 16;
+                calc->calc = rate / div;
+        } else {
+                calc->quot = (rate + (8 * baud)) / (16 * baud);
+                calc->calc = (rate / (calc->quot * 16));
+        }
 
         calc->quot--;
         return 1;
@@ -611,6 +629,30 @@ static unsigned int s3c24xx_serial_getclk(struct uart_port *port,
         return best->quot;
 }
 
+/* udivslot_table[]
+ *
+ * This table takes the fractional value of the baud divisor and gives
+ * the recommended setting for the UDIVSLOT register.
+ */
+static u16 udivslot_table[16] = {
+        [0] = 0x0000,
+        [1] = 0x0080,
+        [2] = 0x0808,
+        [3] = 0x0888,
+        [4] = 0x2222,
+        [5] = 0x4924,
+        [6] = 0x4A52,
+        [7] = 0x54AA,
+        [8] = 0x5555,
+        [9] = 0xD555,
+        [10] = 0xD5D5,
+        [11] = 0xDDD5,
+        [12] = 0xDDDD,
+        [13] = 0xDFDD,
+        [14] = 0xDFDF,
+        [15] = 0xFFDF,
+};
+
 static void s3c24xx_serial_set_termios(struct uart_port *port,
                                        struct ktermios *termios,
                                        struct ktermios *old)
@@ -623,6 +665,7 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
         unsigned int baud, quot;
         unsigned int ulcon;
         unsigned int umcon;
+        unsigned int udivslot = 0;
 
         /*
          * We don't support modem control lines.
@@ -644,6 +687,7 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
         /* check to see if we need  to change clock source */
 
         if (ourport->clksrc != clksrc || ourport->baudclk != clk) {
+                dbg("selecting clock %p\n", clk);
                 s3c24xx_serial_setsource(port, clksrc);
 
                 if (ourport->baudclk != NULL && !IS_ERR(ourport->baudclk)) {
@@ -658,6 +702,13 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
                 ourport->baudclk_rate = clk ? clk_get_rate(clk) : 0;
         }
 
+        if (ourport->info->has_divslot) {
+                unsigned int div = ourport->baudclk_rate / baud;
+
+                udivslot = udivslot_table[div & 15];
+                dbg("udivslot = %04x (div %d)\n", udivslot, div & 15);
+        }
+
         switch (termios->c_cflag & CSIZE) {
         case CS5:
                 dbg("config: 5bits/char\n");
@@ -697,12 +748,16 @@ static void s3c24xx_serial_set_termios(struct uart_port *port,
 
         spin_lock_irqsave(&port->lock, flags);
 
-        dbg("setting ulcon to %08x, brddiv to %d\n", ulcon, quot);
+        dbg("setting ulcon to %08x, brddiv to %d, udivslot %08x\n",
+            ulcon, quot, udivslot);
 
         wr_regl(port, S3C2410_ULCON, ulcon);
         wr_regl(port, S3C2410_UBRDIV, quot);
         wr_regl(port, S3C2410_UMCON, umcon);
 
+        if (ourport->info->has_divslot)
+                wr_regl(port, S3C2443_DIVSLOT, udivslot);
+
         dbg("uart: ulcon = 0x%08x, ucon = 0x%08x, ufcon = 0x%08x\n",
             rd_regl(port, S3C2410_ULCON),
             rd_regl(port, S3C2410_UCON),
diff --git a/drivers/serial/samsung.h b/drivers/serial/samsung.h
index 571d6b90d206..7afb94843a08 100644
--- a/drivers/serial/samsung.h
+++ b/drivers/serial/samsung.h
@@ -21,6 +21,10 @@ struct s3c24xx_uart_info {
         unsigned long           tx_fifoshift;
         unsigned long           tx_fifofull;
 
+        /* uart port features */
+
+        unsigned int            has_divslot:1;
+
         /* clock source control */
 
         int (*get_clksrc)(struct uart_port *, struct s3c24xx_uart_clksrc *clk);