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serial: 8250: Refactor XR17V35X divisor calculation

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Exar XR17V35X PCIe uarts support a 4-bit fractional divisor register.
Refactor the divisor calculation from the divisor programming.

Allow a fractional result from serial8250_get_divisor() and pass this
result to serial8250_dl_write().

Simplify the calculation for quot and quot_frac. This was verified
to be identical to the results of the original calculation with a test
jig.

NB: The results were also compared with the divisor value chart
on pg 33 of the Exar XR17V352 datasheet, rev 1.0.3, here:
http://www.exar.com/common/content/document.ashx?id=1585
which differs from the calculated values by 1 in the fractional result.
This is because the calculated values are still rounded in the
fractional result, whereas the table values are truncated. Note
that the data error rate % values in the datasheet are for
rounded fractional results, as the truncated fractional results
have more error.

Cc: Joe Schultz <jschultz@xes-inc.com>
Cc: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-01-22 12:24:29 -05:00 committed by Greg Kroah-Hartman
parent e72abd5da0
commit 06a4c71067
1 changed files with 30 additions and 22 deletions
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52
drivers/tty/serial/8250/8250_core.c
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@ -2413,7 +2413,26 @@ static void serial8250_shutdown(struct uart_port *port)
serial8250_do_shutdown(port);
}
static unsigned int serial8250_get_divisor(struct uart_8250_port *up, unsigned int baud)
/*
* XR17V35x UARTs have an extra fractional divisor register (DLD)
* Calculate divisor with extra 4-bit fractional portion
*/
static unsigned int xr17v35x_get_divisor(struct uart_8250_port *up,
unsigned int baud,
unsigned int *frac)
{
struct uart_port *port = &up->port;
unsigned int quot_16;
quot_16 = DIV_ROUND_CLOSEST(port->uartclk, baud);
*frac = quot_16 & 0x0f;
return quot_16 >> 4;
}
static unsigned int serial8250_get_divisor(struct uart_8250_port *up,
unsigned int baud,
unsigned int *frac)
{
struct uart_port *port = &up->port;
unsigned int quot;
@ -2421,6 +2440,7 @@ static unsigned int serial8250_get_divisor(struct uart_8250_port *up, unsigned i
/*
* Handle magic divisors for baud rates above baud_base on
* SMSC SuperIO chips.
*
*/
if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
baud == (port->uartclk/4))
@ -2428,6 +2448,8 @@ static unsigned int serial8250_get_divisor(struct uart_8250_port *up, unsigned i
else if ((port->flags & UPF_MAGIC_MULTIPLIER) &&
baud == (port->uartclk/8))
quot = 0x8002;
else if (up->port.type == PORT_XR17V35X)
quot = xr17v35x_get_divisor(up, baud, frac);
else
quot = uart_get_divisor(port, baud);
@ -2479,7 +2501,7 @@ static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,
}
void serial8250_set_divisor(struct uart_port *port, unsigned int baud,
unsigned int quot)
unsigned int quot, unsigned int quot_frac)
{
struct uart_8250_port *up = up_to_u8250p(port);
@ -2503,23 +2525,9 @@ void serial8250_set_divisor(struct uart_port *port, unsigned int baud,
serial_dl_write(up, quot);
/*
* XR17V35x UARTs have an extra fractional divisor register (DLD)
*
* We need to recalculate all of the registers, because DLM and DLL
* are already rounded to a whole integer.
*
* When recalculating we use a 32x clock instead of a 16x clock to
* allow 1-bit for rounding in the fractional part.
*/
if (up->port.type == PORT_XR17V35X) {
unsigned int baud_x32 = (port->uartclk * 2) / baud;
u16 quot = baud_x32 / 32;
u8 quot_frac = DIV_ROUND_CLOSEST(baud_x32 % 32, 2);
serial_dl_write(up, quot);
serial_port_out(port, 0x2, quot_frac & 0xf);
}
/* XR17V35x UARTs have an extra fractional divisor register (DLD) */
if (up->port.type == PORT_XR17V35X)
serial_port_out(port, 0x2, quot_frac);
}
void
@ -2529,7 +2537,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
struct uart_8250_port *up = up_to_u8250p(port);
unsigned char cval;
unsigned long flags;
unsigned int baud, quot;
unsigned int baud, quot, frac = 0;
cval = serial8250_compute_lcr(up, termios->c_cflag);
@ -2539,7 +2547,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
baud = uart_get_baud_rate(port, termios, old,
port->uartclk / 16 / 0xffff,
port->uartclk / 16);
quot = serial8250_get_divisor(up, baud);
quot = serial8250_get_divisor(up, baud, &frac);
if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
/* NOTE: If fifo_bug is not set, a user can set RX_trigger. */
@ -2636,7 +2644,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
serial_port_out(port, UART_EFR, efr);
}
serial8250_set_divisor(port, baud, quot);
serial8250_set_divisor(port, baud, quot, frac);
/*
* LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR