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serial: sh-sci: Support for HSCIF RX sampling point adjustment 

HSCIF has facilities that allow moving the RX sampling point by between
-8 and 7 sampling cycles (one sampling cycles equals 1/15 of a bit
by default) to improve the error margin in case of slightly mismatched
bit rates between sender and receiver.

This patch tries to determine if shifting the sampling point can improve
the error margin and will enable it if so.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ulrich Hecht 2018-04-04 17:48:51 +02:00 committed by Greg Kroah-Hartman
parent 7678f4c20f
commit 63ba1e00f1
2 changed files with 46 additions and 23 deletions
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65
drivers/tty/serial/sh-sci.c
View File

@ -2391,6 +2391,27 @@ done:
uart_update_timeout(port, termios->c_cflag, baud);
/* byte size and parity */
switch (termios->c_cflag & CSIZE) {
case CS5:
bits = 7;
break;
case CS6:
bits = 8;
break;
case CS7:
bits = 9;
break;
default:
bits = 10;
break;
}
if (termios->c_cflag & CSTOPB)
bits++;
if (termios->c_cflag & PARENB)
bits++;
if (best_clk >= 0) {
if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
switch (srr + 1) {
@ -2407,8 +2428,27 @@ done:
serial_port_out(port, SCSCR, scr_val | s->hscif_tot);
serial_port_out(port, SCSMR, smr_val);
serial_port_out(port, SCBRR, brr);
if (sci_getreg(port, HSSRR)->size)
serial_port_out(port, HSSRR, srr | HSCIF_SRE);
if (sci_getreg(port, HSSRR)->size) {
unsigned int hssrr = srr | HSCIF_SRE;
/* Calculate deviation from intended rate at the
* center of the last stop bit in sampling clocks.
*/
int last_stop = bits * 2 - 1;
int deviation = min_err * srr * last_stop / 2 / baud;
if (abs(deviation) >= 2) {
/* At least two sampling clocks off at the
* last stop bit; we can increase the error
* margin by shifting the sampling point.
*/
int shift = min(-8, max(7, deviation / 2));
hssrr |= (shift << HSCIF_SRHP_SHIFT) &
HSCIF_SRHP_MASK;
hssrr |= HSCIF_SRDE;
}
serial_port_out(port, HSSRR, hssrr);
}
/* Wait one bit interval */
udelay((1000000 + (baud - 1)) / baud);
@ -2475,27 +2515,6 @@ done:
* value obtained by this formula is too small. Therefore, if the value
* is smaller than 20ms, use 20ms as the timeout value for DMA.
*/
/* byte size and parity */
switch (termios->c_cflag & CSIZE) {
case CS5:
bits = 7;
break;
case CS6:
bits = 8;
break;
case CS7:
bits = 9;
break;
default:
bits = 10;
break;
}
if (termios->c_cflag & CSTOPB)
bits++;
if (termios->c_cflag & PARENB)
bits++;
s->rx_frame = (10000 * bits) / (baud / 100);
#ifdef CONFIG_SERIAL_SH_SCI_DMA
s->rx_timeout = s->buf_len_rx * 2 * s->rx_frame;

4
drivers/tty/serial/sh-sci.h
View File

@ -130,6 +130,10 @@ enum {
/* HSSRR HSCIF */
#define HSCIF_SRE BIT(15) /* Sampling Rate Register Enable */
#define HSCIF_SRDE BIT(14) /* Sampling Point Register Enable */
#define HSCIF_SRHP_SHIFT 8
#define HSCIF_SRHP_MASK 0x0f00
/* SCPCR (Serial Port Control Register), SCIFA/SCIFB only */
#define SCPCR_RTSC BIT(4) /* Serial Port RTS# Pin / Output Pin */