From patchwork Tue May 19 22:41:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lubomir Rintel X-Patchwork-Id: 11558931 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 387FA13B4 for ; Tue, 19 May 2020 22:42:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29E6D2075F for ; Tue, 19 May 2020 22:42:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726352AbgESWl7 (ORCPT ); Tue, 19 May 2020 18:41:59 -0400 Received: from v6.sk ([167.172.42.174]:58510 "EHLO v6.sk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726318AbgESWl7 (ORCPT ); Tue, 19 May 2020 18:41:59 -0400 Received: from localhost (v6.sk [IPv6:::1]) by v6.sk (Postfix) with ESMTP id 04E49610D3; Tue, 19 May 2020 22:41:57 +0000 (UTC) From: Lubomir Rintel To: Stephen Boyd Cc: Michael Turquette , Rob Herring , linux-clk@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Lubomir Rintel Subject: [PATCH v3 01/13] clk: mmp: frac: Do not lose last 4 digits of precision Date: Wed, 20 May 2020 00:41:39 +0200 Message-Id: <20200519224151.2074597-2-lkundrak@v3.sk> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200519224151.2074597-1-lkundrak@v3.sk> References: <20200519224151.2074597-1-lkundrak@v3.sk> MIME-Version: 1.0 Sender: linux-clk-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-clk@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; }