On the MPC5200B, select the baud rate prescaler as /4 by default to make very
high baud rates (e.g. 3 MBaud) accessible and to achieve a higher precision
for high baud rates in general. For baud rates below ~500 Baud, the code will
automatically fall back to the /32 prescaler. The original MPC5200 does only
have a /32 prescaler which is detected only once and stored in a global. A
new chip-dependent method is used to set the divisor.
Tested on a custom 5200B based board, with up to 3 MBaud.
Signed-off-by: Albrecht Dreß <albrecht.dr...@arcor.de>
---
--- linux-2.6.33/drivers/serial/mpc52xx_uart.c.orig 2010-02-24
19:52:17.000000000 +0100
+++ linux-2.6.33/drivers/serial/mpc52xx_uart.c 2010-02-26 21:12:51.000000000
+0100
@@ -144,9 +144,17 @@ struct psc_ops {
unsigned char (*read_char)(struct uart_port *port);
void (*cw_disable_ints)(struct uart_port *port);
void (*cw_restore_ints)(struct uart_port *port);
+ void (*set_divisor)(struct uart_port *port,
+ unsigned int divisor);
unsigned long (*getuartclk)(void *p);
};
+/* We need to distinguish between the MPC5200 which has only a /32 prescaler,
+ * and the MPC5200B which has a /32 and a /4 prescaler. The global is fine,
+ * as the chip can be only either a 5200B or not. */
+static int is_mpc5200b = -1;
+
+
#ifdef CONFIG_PPC_MPC52xx
#define FIFO_52xx(port) ((struct mpc52xx_psc_fifo __iomem *)(PSC(port)+1))
static void mpc52xx_psc_fifo_init(struct uart_port *port)
@@ -154,9 +162,6 @@ static void mpc52xx_psc_fifo_init(struct
struct mpc52xx_psc __iomem *psc = PSC(port);
struct mpc52xx_psc_fifo __iomem *fifo = FIFO_52xx(port);
- /* /32 prescaler */
- out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00);
-
out_8(&fifo->rfcntl, 0x00);
out_be16(&fifo->rfalarm, 0x1ff);
out_8(&fifo->tfcntl, 0x07);
@@ -245,15 +250,40 @@ static void mpc52xx_psc_cw_restore_ints(
out_be16(&PSC(port)->mpc52xx_psc_imr, port->read_status_mask);
}
+static void mpc52xx_psc_set_divisor(struct uart_port *port,
+ unsigned int divisor)
+{
+ struct mpc52xx_psc __iomem *psc = PSC(port);
+
+ /* prescaler */
+ if (is_mpc5200b != 1)
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */
+ else if (divisor > 0xffff) {
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */
+ divisor = (divisor + 4) / 8;
+ } else
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xff00); /* /4 */
+
+ /* ctr */
+ divisor &= 0xffff;
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
+}
+
/* Search for bus-frequency property in this node or a parent */
static unsigned long mpc52xx_getuartclk(void *p)
{
/*
- * 5200 UARTs have a / 32 prescaler
- * but the generic serial code assumes 16
- * so return ipb freq / 2
+ * The 5200 has only /32 prescalers.
+ * 5200B UARTs have a /4 or a /32 prescaler. For higher accuracy, we
+ * do all calculations using the /4 prescaler for this chip.
+ * The generic serial code assumes /16 so return ipb freq / 2 (5200)
+ * or ipb freq * 4 (5200B).
*/
- return mpc5xxx_get_bus_frequency(p) / 2;
+ if (is_mpc5200b == 1)
+ return mpc5xxx_get_bus_frequency(p) * 4;
+ else
+ return mpc5xxx_get_bus_frequency(p) / 2;
}
static struct psc_ops mpc52xx_psc_ops = {
@@ -272,6 +302,7 @@ static struct psc_ops mpc52xx_psc_ops =
.read_char = mpc52xx_psc_read_char,
.cw_disable_ints = mpc52xx_psc_cw_disable_ints,
.cw_restore_ints = mpc52xx_psc_cw_restore_ints,
+ .set_divisor = mpc52xx_psc_set_divisor,
.getuartclk = mpc52xx_getuartclk,
};
@@ -388,6 +419,16 @@ static void mpc512x_psc_cw_restore_ints(
out_be32(&FIFO_512x(port)->rximr, port->read_status_mask & 0x7f);
}
+static void mpc512x_psc_set_divisor(struct uart_port *port,
+ unsigned int divisor)
+{
+ struct mpc52xx_psc __iomem *psc = PSC(port);
+
+ divisor &= 0xffff;
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
+}
+
static unsigned long mpc512x_getuartclk(void *p)
{
return mpc5xxx_get_bus_frequency(p);
@@ -409,6 +450,7 @@ static struct psc_ops mpc512x_psc_ops =
.read_char = mpc512x_psc_read_char,
.cw_disable_ints = mpc512x_psc_cw_disable_ints,
.cw_restore_ints = mpc512x_psc_cw_restore_ints,
+ .set_divisor = mpc512x_psc_set_divisor,
.getuartclk = mpc512x_getuartclk,
};
#endif
@@ -564,7 +606,6 @@ mpc52xx_uart_set_termios(struct uart_por
struct mpc52xx_psc __iomem *psc = PSC(port);
unsigned long flags;
unsigned char mr1, mr2;
- unsigned short ctr;
unsigned int j, baud, quot;
/* Prepare what we're gonna write */
@@ -604,7 +645,6 @@ mpc52xx_uart_set_termios(struct uart_por
baud = uart_get_baud_rate(port, new, old, 0, port->uartclk/16);
quot = uart_get_divisor(port, baud);
- ctr = quot & 0xffff;
/* Get the lock */
spin_lock_irqsave(&port->lock, flags);
@@ -635,8 +675,7 @@ mpc52xx_uart_set_termios(struct uart_por
out_8(&psc->command, MPC52xx_PSC_SEL_MODE_REG_1);
out_8(&psc->mode, mr1);
out_8(&psc->mode, mr2);
- out_8(&psc->ctur, ctr >> 8);
- out_8(&psc->ctlr, ctr & 0xff);
+ psc_ops->set_divisor(port, quot);
if (UART_ENABLE_MS(port, new->c_cflag))
mpc52xx_uart_enable_ms(port);
@@ -1113,6 +1152,19 @@ mpc52xx_uart_of_probe(struct of_device *
dev_dbg(&op->dev, "mpc52xx_uart_probe(op=%p, match=%p)\n", op, match);
+ /* Check only once if we are running on a mpc5200b or not */
+ if (is_mpc5200b == -1) {
+ struct device_node *np;
+
+ np = of_find_compatible_node(NULL, NULL, "fsl,mpc5200b-immr");
+ if (np) {
+ is_mpc5200b = 1;
+ dev_dbg(&op->dev, "mpc5200b: using /4 prescaler\n");
+ of_node_put(np);
+ } else
+ is_mpc5200b = 0;
+ }
+
/* Check validity & presence */
for (idx = 0; idx < MPC52xx_PSC_MAXNUM; idx++)
if (mpc52xx_uart_nodes[idx] == op->node)
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