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 with a
"virtual" /4 prescaler for all chips for maximum accuracy. A new set_divisor
method scales down the divisor values found by the generic serial code
appropriately.
Note: only "fsl,mpc5200b-psc-uart" compatible devices benefit from these
improvements.
Tested on a custom 5200B based board, with up to 3 MBaud, and with both
"fsl,mpc5200b-psc-uart" and "fsl,mpc5200-psc-uart" devices.
Signed-off-by: Albrecht Dreß <albrecht.dr...@arcor.de>
---
Changes vs. v.1: include improvements suggested by Wolfram and Grant (thanks a
lot for your helpful input!!): drop getuartclk method and use the highest
possible frequency for calculation, use new psc_ops for the 5200b, let the
set_divisor method do all the dirty work, emit warnings if bad divisor values
have been selected.
--- 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 2010-03-03 10:52:04.000000000
+0100
@@ -144,7 +144,8 @@ 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);
+ void (*set_divisor)(struct uart_port *port,
+ unsigned int divisor);
};
#ifdef CONFIG_PPC_MPC52xx
@@ -154,9 +155,6 @@ 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 +243,55 @@ 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)
+static void mpc52xx_psc_set_divisor(struct uart_port *port,
+ unsigned int divisor)
{
- /*
- * 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;
+ struct mpc52xx_psc __iomem *psc = PSC(port);
+
+ /* adjust divisor for a /32 prescaler; see note in
+ * mpc52xx_uart_of_probe() */
+ divisor = (divisor + 4) / 8;
+ if (divisor > 0xffff) {
+ pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__,
+ divisor);
+ divisor = 0xffff;
+ } else if (divisor == 0) {
+ pr_warning("%s: divisor 0, use 1\n", __func__);
+ divisor = 1;
+ }
+
+ /* prescaler */
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */
+
+ /* ctr */
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
+}
+
+static void mpc5200b_psc_set_divisor(struct uart_port *port,
+ unsigned int divisor)
+{
+ struct mpc52xx_psc __iomem *psc = PSC(port);
+
+ /* set prescaler; see note in mpc52xx_uart_of_probe() */
+ if (divisor > 0xffff) {
+ divisor = (divisor + 4) / 8;
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xdd00); /* /32 */
+ } else
+ out_be16(&psc->mpc52xx_psc_clock_select, 0xff00); /* /4 */
+
+ if (divisor > 0xffff) {
+ pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__,
+ divisor);
+ divisor = 0xffff;
+ } else if (divisor == 0) {
+ pr_warning("%s: divisor 0, use 1\n", __func__);
+ divisor = 1;
+ }
+
+ /* ctr */
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
}
static struct psc_ops mpc52xx_psc_ops = {
@@ -272,7 +310,26 @@ 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_divisor = mpc52xx_psc_set_divisor,
+};
+
+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_divisor = mpc5200b_psc_set_divisor,
};
#endif /* CONFIG_MPC52xx */
@@ -388,9 +445,25 @@ 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 void mpc512x_psc_set_divisor(struct uart_port *port,
+ unsigned int divisor)
{
- return mpc5xxx_get_bus_frequency(p);
+ struct mpc52xx_psc __iomem *psc = PSC(port);
+
+ /* adjust divisor for a /16 prescaler; see note in
+ * mpc52xx_uart_of_probe() */
+ divisor = (divisor + 2) / 4;
+ if (divisor > 0xffff) {
+ pr_warning("%s: divisor overflow (%x), use 0xffff\n", __func__,
+ divisor);
+ divisor = 0xffff;
+ } else if (divisor == 0) {
+ pr_warning("%s: divisor 0, use 1\n", __func__);
+ divisor = 1;
+ }
+
+ out_8(&psc->ctur, divisor >> 8);
+ out_8(&psc->ctlr, divisor & 0xff);
}
static struct psc_ops mpc512x_psc_ops = {
@@ -409,7 +482,7 @@ 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_divisor = mpc512x_psc_set_divisor,
};
#endif
@@ -564,7 +637,6 @@ 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 +676,6 @@ 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 +706,7 @@ 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);
@@ -1007,7 +1077,8 @@ mpc52xx_console_setup(struct console *co
return ret;
}
- uartclk = psc_ops->getuartclk(np);
+ /* see remarks about the uart clock in mpc52xx_uart_of_probe() */
+ uartclk = mpc5xxx_get_bus_frequency(np) * 4;
if (uartclk == 0) {
pr_debug("Could not find uart clock frequency!\n");
return -EINVAL;
@@ -1090,6 +1161,7 @@ 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 +1194,24 @@ 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);
+ /*
+ * Note about the uart clock:
+ * This series of processors use the ipb clock frequency for the clock
+ * generation scaled down by prescalers and a 16-bit counter register:
+ * - the 5200 has a /32 prescaler
+ * - the 5200B has selectable /4 or /32 prescalers (i.e. the counter
+ * reg can be viewed as a 19-bit value, of which we can use either
+ * the upper or the lower 16 bits - in the latter case the three
+ * MSB's must of course be 0)
+ * - the 512x has a /16 prescaler
+ * The generic serial code assumes a prescaler of /16. As we want to
+ * achieve the maximum accuracy possible, we let the generic serial
+ * code perform all calculations with the /4 prescaler, i.e. we have
+ * to set the uart clock to ipb freq * 4 here. The set_divisor methods
+ * for the different chips are responsible for scaling down the divisor
+ * value appropriately.
+ */
+ uartclk = mpc5xxx_get_bus_frequency(op->node) * 4;
if (uartclk == 0) {
dev_dbg(&op->dev, "Could not find uart clock frequency!\n");
return -EINVAL;
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
