From patchwork Mon Dec 14 18:57:22 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 7846761 X-Patchwork-Delegate: geert@linux-m68k.org Return-Path: X-Original-To: patchwork-linux-sh@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 6808BBEEE1 for ; Mon, 14 Dec 2015 18:57:47 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 66F8720382 for ; Mon, 14 Dec 2015 18:57:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43829202E9 for ; Mon, 14 Dec 2015 18:57:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932077AbbLNS5o (ORCPT ); Mon, 14 Dec 2015 13:57:44 -0500 Received: from albert.telenet-ops.be ([195.130.137.90]:55505 "EHLO albert.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753306AbbLNS5o (ORCPT ); Mon, 14 Dec 2015 13:57:44 -0500 Received: from ayla.of.borg ([84.195.106.123]) by albert.telenet-ops.be with bizsmtp id tWxi1r00N2fm56U06Wxipi; Mon, 14 Dec 2015 19:57:43 +0100 Received: from ramsan.of.borg ([192.168.97.29] helo=ramsan) by ayla.of.borg with esmtp (Exim 4.82) (envelope-from ) id 1a8YJa-0002to-73; Mon, 14 Dec 2015 19:57:42 +0100 Received: from geert by ramsan with local (Exim 4.82) (envelope-from ) id 1a8YJd-0000Hd-LI; Mon, 14 Dec 2015 19:57:45 +0100 From: Geert Uytterhoeven To: Greg Kroah-Hartman , Simon Horman , Magnus Damm , Yoshinori Sato Cc: linux-serial@vger.kernel.org, linux-sh@vger.kernel.org, Geert Uytterhoeven Subject: [PATCH v3 13/27] serial: sh-sci: Improve bit rate error calculation for HSCIF Date: Mon, 14 Dec 2015 19:57:22 +0100 Message-Id: <1450119456-964-14-git-send-email-geert+renesas@glider.be> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1450119456-964-1-git-send-email-geert+renesas@glider.be> References: <1450119456-964-1-git-send-email-geert+renesas@glider.be> Sender: linux-sh-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The algorithm to find the best parameters for the requested bit rate calculates the relative bit rate error, using "(br * scrate) / 1000". For small "br * scrate", this has two problems: - The quotient may be zero, leading to a division by zero error, - This may introduce a large rounding error. Switch from relative to absolute bit rate error calculation to fix this. The default baud rate generator values can be removed, as there will always be one set of values that gives the smallest absolute error. Print the best set of values when debugging. Signed-off-by: Geert Uytterhoeven Acked-by: Greg Kroah-Hartman --- v3: - Add Acked-by, - Update for rename of intermediates to "prediv" and "scrate". --- drivers/tty/serial/sh-sci.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index c490c51d6032786b..306497ee5c326d19 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1867,12 +1867,13 @@ static unsigned int sci_scbrr_calc(struct sci_port *s, unsigned int bps, } /* calculate sample rate, BRR, and clock select for HSCIF */ -static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq, int *brr, +static void sci_baud_calc_hscif(struct sci_port *s, unsigned int bps, + unsigned long freq, int *brr, unsigned int *srr, unsigned int *cks) { unsigned int sr, br, prediv, scrate, c; int err, recv_margin; - int min_err = 1000; /* 100% */ + int min_err = INT_MAX; int recv_max_margin = 0; /* Find the combination of sample rate and clock select with the @@ -1886,7 +1887,7 @@ static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq, int *brr, * We need to calculate: * * br = freq / (prediv * bps) clamped to [1..256] - * err = (freq / (br * prediv * bps / 1000)) - 1000 + * err = freq / (br * prediv) - bps * * Watch out for overflow when calculating the desired * sampling clock rate! @@ -1897,8 +1898,7 @@ static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq, int *brr, scrate = prediv * bps; br = DIV_ROUND_CLOSEST(freq, scrate); br = clamp(br, 1U, 256U); - err = DIV_ROUND_CLOSEST(freq, (br * scrate) / 1000) - - 1000; + err = DIV_ROUND_CLOSEST(freq, br * prediv) - bps; /* Calc recv margin * M: Receive margin (%) * N: Ratio of bit rate to clock (N = sampling rate) @@ -1928,13 +1928,8 @@ static void sci_baud_calc_hscif(unsigned int bps, unsigned long freq, int *brr, } } - if (min_err == 1000) { - WARN_ON(1); - /* use defaults */ - *brr = 255; - *srr = 15; - *cks = 0; - } + dev_dbg(s->port.dev, "BRR: %u%+d bps using N %u SR %u cks %u\n", bps, + min_err, *brr, *srr + 1, *cks); } static void sci_reset(struct uart_port *port) @@ -1984,7 +1979,7 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, baud = uart_get_baud_rate(port, termios, old, 0, max_baud); if (likely(baud && port->uartclk)) { if (s->cfg->type == PORT_HSCIF) { - sci_baud_calc_hscif(baud, port->uartclk, &t, &srr, + sci_baud_calc_hscif(s, baud, port->uartclk, &t, &srr, &cks); } else { t = sci_scbrr_calc(s, baud, port->uartclk);