From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:33661 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752013AbeDDPs4 (ORCPT ); Wed, 4 Apr 2018 11:48:56 -0400 From: Ulrich Hecht To: linux-renesas-soc@vger.kernel.org, wsa@the-dreams.de, geert@linux-m68k.org Cc: linux-serial@vger.kernel.org, magnus.damm@gmail.com, greg@kroah.com, Ulrich Hecht Subject: [PATCH v2] serial: sh-sci: Support for HSCIF RX sampling point adjustment Date: Wed, 4 Apr 2018 17:48:51 +0200 Message-Id: <1522856931-6225-1-git-send-email-ulrich.hecht+renesas@gmail.com> Sender: linux-renesas-soc-owner@vger.kernel.org List-ID: 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 --- This revision dumps the sysfs interface and works out the optimal shift on its own. It also moves setting of the HSSRR register back to its original location. CU Uli drivers/tty/serial/sh-sci.c | 65 +++++++++++++++++++++++++++++---------------- drivers/tty/serial/sh-sci.h | 4 +++ 2 files changed, 46 insertions(+), 23 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index fdbbff5..5d61654 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -2390,6 +2390,27 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, 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) { @@ -2406,8 +2427,27 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, 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); @@ -2474,27 +2514,6 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, * 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; diff --git a/drivers/tty/serial/sh-sci.h b/drivers/tty/serial/sh-sci.h index a5f792f..0b9e804 100644 --- a/drivers/tty/serial/sh-sci.h +++ b/drivers/tty/serial/sh-sci.h @@ -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 */ -- 2.7.4