From patchwork Mon May 11 19:25:08 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lubomir Rintel X-Patchwork-Id: 200784 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60A36C47255 for ; Mon, 11 May 2020 19:25:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47F252075E for ; Mon, 11 May 2020 19:25:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731440AbgEKTZc (ORCPT ); Mon, 11 May 2020 15:25:32 -0400 Received: from v6.sk ([167.172.42.174]:52328 "EHLO v6.sk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729453AbgEKTZa (ORCPT ); Mon, 11 May 2020 15:25:30 -0400 Received: from localhost (v6.sk [IPv6:::1]) by v6.sk (Postfix) with ESMTP id 484A4610CF; Mon, 11 May 2020 19:25:29 +0000 (UTC) From: Lubomir Rintel To: Michael Turquette Cc: Stephen Boyd , Rob Herring , linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, Lubomir Rintel Subject: [PATCH v2 01/10] clk: mmp: frac: Do not lose last 4 digits of precision Date: Mon, 11 May 2020 21:25:08 +0200 Message-Id: <20200511192517.1206442-2-lkundrak@v3.sk> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200511192517.1206442-1-lkundrak@v3.sk> References: <20200511192517.1206442-1-lkundrak@v3.sk> MIME-Version: 1.0 Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org While calculating the output rate of a fractional divider clock, the value is divided and multipled by 10000, discarding the least significant digits -- presumably to fit the intermediate value within 32 bits. The precision we're losing is, however, not insignificant for things like I2S clock. Maybe also elsewhere, now that since commit ea56ad60260e ("clk: mmp2: Stop pretending PLL outputs are constant") the parent rates are more precise and no longer rounded to 10000s. Signed-off-by: Lubomir Rintel --- drivers/clk/mmp/clk-frac.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/clk/mmp/clk-frac.c b/drivers/clk/mmp/clk-frac.c index fabc09aca6c4..ed9928f5bdc7 100644 --- a/drivers/clk/mmp/clk-frac.c +++ b/drivers/clk/mmp/clk-frac.c @@ -28,13 +28,15 @@ static long clk_factor_round_rate(struct clk_hw *hw, unsigned long drate, unsigned long *prate) { struct mmp_clk_factor *factor = to_clk_factor(hw); - unsigned long rate = 0, prev_rate; + u64 rate = 0, prev_rate; int i; for (i = 0; i < factor->ftbl_cnt; i++) { prev_rate = rate; - rate = (((*prate / 10000) * factor->ftbl[i].den) / - (factor->ftbl[i].num * factor->masks->factor)) * 10000; + rate = *prate; + rate *= factor->ftbl[i].den; + do_div(rate, factor->ftbl[i].num * factor->masks->factor); + if (rate > drate) break; } @@ -54,6 +56,7 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw, struct mmp_clk_factor *factor = to_clk_factor(hw); struct mmp_clk_factor_masks *masks = factor->masks; unsigned int val, num, den; + u64 rate; val = readl_relaxed(factor->base); @@ -66,8 +69,11 @@ static unsigned long clk_factor_recalc_rate(struct clk_hw *hw, if (!den) return 0; - return (((parent_rate / 10000) * den) / - (num * factor->masks->factor)) * 10000; + rate = parent_rate; + rate *= den; + do_div(rate, num * factor->masks->factor); + + return rate; } /* Configures new clock rate*/ @@ -78,12 +84,14 @@ static int clk_factor_set_rate(struct clk_hw *hw, unsigned long drate, struct mmp_clk_factor_masks *masks = factor->masks; int i; unsigned long val; - unsigned long rate = 0; unsigned long flags = 0; + u64 rate = 0; for (i = 0; i < factor->ftbl_cnt; i++) { - rate = (((prate / 10000) * factor->ftbl[i].den) / - (factor->ftbl[i].num * factor->masks->factor)) * 10000; + rate = prate; + rate *= factor->ftbl[i].den; + do_div(rate, factor->ftbl[i].num * factor->masks->factor); + if (rate > drate) break; }