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powerpc/5200: improve uart baud rate calculation (reach high baud rat…
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…es, better accuracy)

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.

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.
Also tested on the mpc5121ads board.

Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>
[agust: fixed mpc5121 prescaler comment]
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
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Albrecht Dreß authored and Grant Likely committed Jul 25, 2010
1 parent b37fa16 commit 0d1f22e
Showing 1 changed file with 116 additions and 29 deletions.
145 changes: 116 additions & 29 deletions drivers/serial/mpc52xx_uart.c
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Original file line number Diff line number Diff line change
Expand Up @@ -113,24 +113,33 @@ 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);
int (*clock)(struct uart_port *port, int enable);
int (*fifoc_init)(void);
void (*fifoc_uninit)(void);
void (*get_irq)(struct uart_port *, struct device_node *);
irqreturn_t (*handle_irq)(struct uart_port *port);
};

/* 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)
{
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);
Expand Down Expand Up @@ -219,15 +228,47 @@ static void mpc52xx_psc_cw_restore_ints(struct uart_port *port)
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 unsigned int mpc5200_psc_set_baudrate(struct uart_port *port,
struct ktermios *new,
struct ktermios *old)
{
/*
* 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;
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 void mpc52xx_psc_get_irq(struct uart_port *port, struct device_node *np)
Expand Down Expand Up @@ -258,7 +299,28 @@ 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,
.get_irq = mpc52xx_psc_get_irq,
.handle_irq = mpc52xx_psc_handle_irq,
};

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,
.get_irq = mpc52xx_psc_get_irq,
.handle_irq = mpc52xx_psc_handle_irq,
};
Expand Down Expand Up @@ -392,9 +454,35 @@ static void mpc512x_psc_cw_restore_ints(struct uart_port *port)
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;

/*
* 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. This is wrong.
*
* In reality using /32 prescaler doesn't work, as it is not supported!
* Use /16 or /10 prescaler, see "MPC5121e Hardware Design Guide",
* Chapter 4.1 PSC in UART Mode.
* Calculate with a /16 prescaler here.
*/

/* 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);

/* enable the /16 prescaler and set the divisor */
mpc52xx_set_divisor(PSC(port), 0xdd00, divisor);
return baud;
}

/* Init PSC FIFO Controller */
Expand Down Expand Up @@ -498,7 +586,7 @@ 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,
.clock = mpc512x_psc_clock,
.fifoc_init = mpc512x_psc_fifoc_init,
.fifoc_uninit = mpc512x_psc_fifoc_uninit,
Expand Down Expand Up @@ -666,8 +754,8 @@ mpc52xx_uart_set_termios(struct uart_port *port, struct ktermios *new,
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;
Expand Down Expand Up @@ -704,16 +792,9 @@ mpc52xx_uart_set_termios(struct uart_port *port, struct ktermios *new,
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 */
Expand All @@ -737,8 +818,10 @@ mpc52xx_uart_set_termios(struct uart_port *port, struct ktermios *new,
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);
Expand Down Expand Up @@ -1118,7 +1201,7 @@ mpc52xx_console_setup(struct console *co, char *options)
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;
Expand Down Expand Up @@ -1201,6 +1284,7 @@ static struct uart_driver mpc52xx_uart_driver = {

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, },
Expand Down Expand Up @@ -1233,7 +1317,10 @@ mpc52xx_uart_of_probe(struct of_device *op, const struct of_device_id *match)
pr_debug("Found %s assigned to ttyPSC%x\n",
mpc52xx_uart_nodes[idx]->full_name, idx);

uartclk = psc_ops->getuartclk(op->dev.of_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->dev.of_node);
if (uartclk == 0) {
dev_dbg(&op->dev, "Could not find uart clock frequency!\n");
return -EINVAL;
Expand Down

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