[Patch v.3] mpc5200b/uart: improve baud rate calculation (reach high baud rates, better accuracy)
Albrecht Dreß
albrecht.dress at arcor.de
Fri Mar 5 06:00:14 EST 2010
On the MPC5200B, make very high baud rates (e.g. 3 MBaud) accessible and
achieve a higher precision for high baud rates in general. This is done by
selecting the appropriate prescaler (/4 or /32). As to keep the code clean,
the getuartclk method has been dropped, and all calculations are done in a
new set_baudrate method.
Notes: only "fsl,mpc5200b-psc-uart" compatible devices benefit from these
improvements.
The 512x may or may not work; the patch keeps the current implementation
(using a /16 prescaler), but according to the data sheet, this is plain
wrong. See the comment in mpc512x_psc_set_baudrate(). Any insight and
testing of the code would be appreciated.
Tested on a custom 5200B based board, from 110 baud up to 3 MBaud, and with
both "fsl,mpc5200b-psc-uart" and "fsl,mpc5200-psc-uart" devices.
Signed-off-by: Albrecht Dreß <albrecht.dress at arcor.de>
---
Changes vs. v.2: Pick up Grant's comments by shifting the calculations to the
new set_baudrate method.
--- linux-2.6.33-orig/drivers/serial/mpc52xx_uart.c 2010-02-24 19:52:17.000000000 +0100
+++ linux-2.6.33/drivers/serial/mpc52xx_uart.c 2010-03-04 17:13:47.000000000 +0100
@@ -144,9 +144,21 @@ 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);
- unsigned long (*getuartclk)(void *p);
+ unsigned int (*set_baudrate)(struct uart_port *port,
+ struct ktermios *new,
+ struct ktermios *old);
};
+/* setting the prescaler and divisor reg is common for all chips */
+static inline void mpc52xx_set_divisor(struct mpc52xx_psc __iomem *psc,
+ u16 prescaler, unsigned int divisor)
+{
+ /* select prescaler */
+ out_be16(&psc->mpc52xx_psc_clock_select, prescaler);
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
+}
+
#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 +166,6 @@ 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 +254,47 @@ static void mpc52xx_psc_cw_restore_ints(
out_be16(&PSC(port)->mpc52xx_psc_imr, port->read_status_mask);
}
-/* 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
- */
- return mpc5xxx_get_bus_frequency(p) / 2;
+static unsigned int mpc5200_psc_set_baudrate(struct uart_port *port,
+ struct ktermios *new,
+ struct ktermios *old)
+{
+ unsigned int baud;
+ unsigned int divisor;
+
+ /* The 5200 has a fixed /32 prescaler, uartclk contains the ipb freq */
+ baud = uart_get_baud_rate(port, new, old,
+ port->uartclk / (32 * 0xffff) + 1,
+ port->uartclk / 32);
+ divisor = (port->uartclk + 16 * baud) / (32 * baud);
+
+ /* enable the /32 prescaler and set the divisor */
+ mpc52xx_set_divisor(PSC(port), 0xdd00, divisor);
+ return baud;
+}
+
+static unsigned int mpc5200b_psc_set_baudrate(struct uart_port *port,
+ struct ktermios *new,
+ struct ktermios *old)
+{
+ unsigned int baud;
+ unsigned int divisor;
+ u16 prescaler;
+
+ /* The 5200B has a selectable /4 or /32 prescaler, uartclk contains the
+ * ipb freq */
+ baud = uart_get_baud_rate(port, new, old,
+ port->uartclk / (32 * 0xffff) + 1,
+ port->uartclk / 4);
+ divisor = (port->uartclk + 2 * baud) / (4 * baud);
+
+ /* select the proper prescaler and set the divisor */
+ if (divisor > 0xffff) {
+ divisor = (divisor + 4) / 8;
+ prescaler = 0xdd00; /* /32 */
+ } else
+ prescaler = 0xff00; /* /4 */
+ mpc52xx_set_divisor(PSC(port), prescaler, divisor);
+ return baud;
}
static struct psc_ops mpc52xx_psc_ops = {
@@ -272,7 +313,26 @@ 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,
- .getuartclk = mpc52xx_getuartclk,
+ .set_baudrate = mpc5200_psc_set_baudrate,
+};
+
+static struct psc_ops mpc5200b_psc_ops = {
+ .fifo_init = mpc52xx_psc_fifo_init,
+ .raw_rx_rdy = mpc52xx_psc_raw_rx_rdy,
+ .raw_tx_rdy = mpc52xx_psc_raw_tx_rdy,
+ .rx_rdy = mpc52xx_psc_rx_rdy,
+ .tx_rdy = mpc52xx_psc_tx_rdy,
+ .tx_empty = mpc52xx_psc_tx_empty,
+ .stop_rx = mpc52xx_psc_stop_rx,
+ .start_tx = mpc52xx_psc_start_tx,
+ .stop_tx = mpc52xx_psc_stop_tx,
+ .rx_clr_irq = mpc52xx_psc_rx_clr_irq,
+ .tx_clr_irq = mpc52xx_psc_tx_clr_irq,
+ .write_char = mpc52xx_psc_write_char,
+ .read_char = mpc52xx_psc_read_char,
+ .cw_disable_ints = mpc52xx_psc_cw_disable_ints,
+ .cw_restore_ints = mpc52xx_psc_cw_restore_ints,
+ .set_baudrate = mpc5200b_psc_set_baudrate,
};
#endif /* CONFIG_MPC52xx */
@@ -388,9 +448,44 @@ static void mpc512x_psc_cw_restore_ints(
out_be32(&FIFO_512x(port)->rximr, port->read_status_mask & 0x7f);
}
-static unsigned long mpc512x_getuartclk(void *p)
+static unsigned int mpc512x_psc_set_baudrate(struct uart_port *port,
+ struct ktermios *new,
+ struct ktermios *old)
{
- return mpc5xxx_get_bus_frequency(p);
+ unsigned int baud;
+ unsigned int divisor;
+
+ /*
+ * FIXME -
+ * since ages, the code calculates with a /16 prescaler, but
+ * never configures it explicitly. The "MPC5121e Microcontroller
+ * Reference Manual, Rev. 3" says on pg. 30-10 that the chip supports a
+ * /32 and a /10 prescaler. Furthermore, it states that "After reset,
+ * the prescaler by 10 for the UART mode is selected", but the reset
+ * register value is 0x0000 which means a /32 prescaler...
+ *
+ * Thus, using /16 for the calculation might actually be wrong.
+ *
+ * However, U-Boot (in the file cpu/mpc512x/serial.c) also uses a /16
+ * prescaler, activated by 0xdd00 in the csr.
+ *
+ * **Confusion Alert**
+ *
+ * Unfortunately, I don't have a 512x system, so I cannot say what
+ * happens in reality...
+ *
+ * Albrecht Dreß <albrecht.dress at arcor.de>, 2010-MAR-04
+ */
+
+ /* uartclk contains the ips freq */
+ baud = uart_get_baud_rate(port, new, old,
+ port->uartclk / (16 * 0xffff) + 1,
+ port->uartclk / 16);
+ divisor = (port->uartclk + 8 * baud) / (16 * baud);
+
+ /* FIXME - see above, shamelessly stolen from U-Boot */
+ mpc52xx_set_divisor(PSC(port), 0xdd00, divisor);
+ return baud;
}
static struct psc_ops mpc512x_psc_ops = {
@@ -409,7 +504,7 @@ 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,
- .getuartclk = mpc512x_getuartclk,
+ .set_baudrate = mpc512x_psc_set_baudrate,
};
#endif
@@ -564,8 +659,8 @@ 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;
+ unsigned int j;
+ unsigned int baud;
/* Prepare what we're gonna write */
mr1 = 0;
@@ -602,16 +697,9 @@ mpc52xx_uart_set_termios(struct uart_por
mr2 |= MPC52xx_PSC_MODE_TXCTS;
}
- 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);
- /* Update the per-port timeout */
- uart_update_timeout(port, new->c_cflag, baud);
-
/* Do our best to flush TX & RX, so we don't lose anything */
/* But we don't wait indefinitely ! */
j = 5000000; /* Maximum wait */
@@ -635,8 +723,10 @@ 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);
+ baud = psc_ops->set_baudrate(port, new, old);
+
+ /* Update the per-port timeout */
+ uart_update_timeout(port, new->c_cflag, baud);
if (UART_ENABLE_MS(port, new->c_cflag))
mpc52xx_uart_enable_ms(port);
@@ -1007,7 +1097,7 @@ mpc52xx_console_setup(struct console *co
return ret;
}
- uartclk = psc_ops->getuartclk(np);
+ uartclk = mpc5xxx_get_bus_frequency(np);
if (uartclk == 0) {
pr_debug("Could not find uart clock frequency!\n");
return -EINVAL;
@@ -1090,6 +1180,7 @@ static struct uart_driver mpc52xx_uart_d
static struct of_device_id mpc52xx_uart_of_match[] = {
#ifdef CONFIG_PPC_MPC52xx
+ { .compatible = "fsl,mpc5200b-psc-uart", .data = &mpc5200b_psc_ops, },
{ .compatible = "fsl,mpc5200-psc-uart", .data = &mpc52xx_psc_ops, },
/* binding used by old lite5200 device trees: */
{ .compatible = "mpc5200-psc-uart", .data = &mpc52xx_psc_ops, },
@@ -1122,7 +1213,10 @@ mpc52xx_uart_of_probe(struct of_device *
pr_debug("Found %s assigned to ttyPSC%x\n",
mpc52xx_uart_nodes[idx]->full_name, idx);
- uartclk = psc_ops->getuartclk(op->node);
+ /* set the uart clock to the input clock of the psc, the different
+ * prescalers are taken into account in the set_baudrate() methods
+ * of the respective chip */
+ uartclk = mpc5xxx_get_bus_frequency(op->node);
if (uartclk == 0) {
dev_dbg(&op->dev, "Could not find uart clock frequency!\n");
return -EINVAL;
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