From patchwork Mon Dec 14 18:57:23 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Geert Uytterhoeven X-Patchwork-Id: 7847101 X-Patchwork-Delegate: geert@linux-m68k.org Return-Path: X-Original-To: patchwork-linux-sh@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 7700F9F3CD for ; Mon, 14 Dec 2015 18:59:09 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 7DA8820386 for ; Mon, 14 Dec 2015 18:59:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C133720382 for ; Mon, 14 Dec 2015 18:59:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932153AbbLNS67 (ORCPT ); Mon, 14 Dec 2015 13:58:59 -0500 Received: from andre.telenet-ops.be ([195.130.132.53]:45715 "EHLO andre.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932162AbbLNS5r (ORCPT ); Mon, 14 Dec 2015 13:57:47 -0500 Received: from ayla.of.borg ([84.195.106.123]) by andre.telenet-ops.be with bizsmtp id tWxi1r00u2fm56U01WxiUe; 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-0002tq-7h; Mon, 14 Dec 2015 19:57:42 +0100 Received: from geert by ramsan with local (Exim 4.82) (envelope-from ) id 1a8YJd-0000Hi-Lz; 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 14/27] serial: sh-sci: Avoid calculating the receive margin for HSCIF Date: Mon, 14 Dec 2015 19:57:23 +0100 Message-Id: <1450119456-964-15-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 When assuming D = 0.5 and F = 0, maximizing the receive margin M is equivalent to maximizing the sample rate N. Hence there's no need to calculate the receive margin, as we can obtain the same result by iterating over all possible sample rates in reverse order, and skipping parameter sets that don't provide a lower bit rate error. Signed-off-by: Geert Uytterhoeven Acked-by: Greg Kroah-Hartman --- v3: - Add Acked-by, - Rebased, - Terminate loop over sampling rates on perfect match. --- drivers/tty/serial/sh-sci.c | 51 +++++++++++++++++++++------------------------ 1 file changed, 24 insertions(+), 27 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 306497ee5c326d19..c3a193616484a62c 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1872,13 +1872,24 @@ static void sci_baud_calc_hscif(struct sci_port *s, unsigned int bps, unsigned int *srr, unsigned int *cks) { unsigned int sr, br, prediv, scrate, c; - int err, recv_margin; - int min_err = INT_MAX; - int recv_max_margin = 0; + int err, min_err = INT_MAX; - /* Find the combination of sample rate and clock select with the - smallest deviation from the desired baud rate. */ - for (sr = 8; sr <= 32; sr++) { + /* + * Find the combination of sample rate and clock select with the + * smallest deviation from the desired baud rate. + * Prefer high sample rates to maximise the receive margin. + * + * M: Receive margin (%) + * N: Ratio of bit rate to clock (N = sampling rate) + * D: Clock duty (D = 0 to 1.0) + * L: Frame length (L = 9 to 12) + * F: Absolute value of clock frequency deviation + * + * M = |(0.5 - 1 / 2 * N) - ((L - 0.5) * F) - + * (|D - 0.5| / N * (1 + F))| + * NOTE: Usually, treat D for 0.5, F is 0 by this calculation. + */ + for (sr = 32; sr >= 8; sr--) { for (c = 0; c <= 3; c++) { /* integerized formulas from HSCIF documentation */ prediv = sr * (1 << (2 * c + 1)); @@ -1898,36 +1909,22 @@ static void sci_baud_calc_hscif(struct sci_port *s, unsigned int bps, scrate = prediv * bps; br = DIV_ROUND_CLOSEST(freq, scrate); br = clamp(br, 1U, 256U); + err = DIV_ROUND_CLOSEST(freq, br * prediv) - bps; - /* Calc recv margin - * M: Receive margin (%) - * N: Ratio of bit rate to clock (N = sampling rate) - * D: Clock duty (D = 0 to 1.0) - * L: Frame length (L = 9 to 12) - * F: Absolute value of clock frequency deviation - * - * M = |(0.5 - 1 / 2 * N) - ((L - 0.5) * F) - - * (|D - 0.5| / N * (1 + F))| - * NOTE: Usually, treat D for 0.5, F is 0 by this - * calculation. - */ - recv_margin = abs((500 - - DIV_ROUND_CLOSEST(1000, sr << 1)) / 10); - if (abs(min_err) > abs(err)) { - min_err = err; - recv_max_margin = recv_margin; - } else if ((min_err == err) && - (recv_margin > recv_max_margin)) - recv_max_margin = recv_margin; - else + if (abs(err) >= abs(min_err)) continue; + min_err = err; *brr = br - 1; *srr = sr - 1; *cks = c; + + if (!err) + goto found; } } +found: dev_dbg(s->port.dev, "BRR: %u%+d bps using N %u SR %u cks %u\n", bps, min_err, *brr, *srr + 1, *cks); }