Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753656AbeAJTh6 (ORCPT + 1 other); Wed, 10 Jan 2018 14:37:58 -0500 Received: from mailoutvs3.siol.net ([213.250.19.136]:39634 "EHLO mail.siol.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753278AbeAJTZ1 (ORCPT ); Wed, 10 Jan 2018 14:25:27 -0500 From: Jernej Skrabec To: maxime.ripard@free-electrons.com, airlied@linux.ie, robh+dt@kernel.org, mark.rutland@arm.com, wens@csie.org, architt@codeaurora.org, a.hajda@samsung.com, Laurent.pinchart@ideasonboard.com Cc: mturquette@baylibre.com, sboyd@codeaurora.org, Jose.Abreu@synopsys.com, narmstrong@baylibre.com, jernej.skrabec@siol.net, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org, linux-sunxi@googlegroups.com Subject: [PATCH v2 02/12] clk: sunxi-ng: Change formula for NKMP PLLs Date: Wed, 10 Jan 2018 20:25:02 +0100 Message-Id: <20180110192512.19684-3-jernej.skrabec@siol.net> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180110192512.19684-1-jernej.skrabec@siol.net> References: <20180110192512.19684-1-jernej.skrabec@siol.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: This commit changes formula from this: Freq = (parent_freq * N * K) / (M * P) to this: Freq = (parent_freq / M) * N * K / P This improves situation when N is in the range 1-255. PLL parent clock is almost always 24 MHz, which means that for N >= 180 original formula overflows and result becomes useless. Situation can be improved if M is used as predivider as it can be seen in the second formula. That way at least M > 1 is considered, but it still leaves small gap for wrong result when M = 1 and N >= 180. Using M as predivider shouldn't cause any issue, because it is in range 1-4 at most, so there is no or only minimal rounding error. Signed-off-by: Jernej Skrabec --- drivers/clk/sunxi-ng/ccu_nkmp.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/clk/sunxi-ng/ccu_nkmp.c b/drivers/clk/sunxi-ng/ccu_nkmp.c index a99068a08315..e6c996ad4483 100644 --- a/drivers/clk/sunxi-ng/ccu_nkmp.c +++ b/drivers/clk/sunxi-ng/ccu_nkmp.c @@ -33,7 +33,7 @@ static void ccu_nkmp_find_best(unsigned long parent, unsigned long rate, for (_p = nkmp->min_p; _p <= nkmp->max_p; _p <<= 1) { unsigned long tmp_rate; - tmp_rate = parent * _n * _k / (_m * _p); + tmp_rate = (parent / _m) * _n * _k / _p; if (tmp_rate > rate) continue; @@ -107,7 +107,7 @@ static unsigned long ccu_nkmp_recalc_rate(struct clk_hw *hw, p = reg >> nkmp->p.shift; p &= (1 << nkmp->p.width) - 1; - return (parent_rate * n * k >> p) / m; + return (parent_rate / m) * n * k >> p; } static long ccu_nkmp_round_rate(struct clk_hw *hw, unsigned long rate, @@ -127,7 +127,7 @@ static long ccu_nkmp_round_rate(struct clk_hw *hw, unsigned long rate, ccu_nkmp_find_best(*parent_rate, rate, &_nkmp); - return *parent_rate * _nkmp.n * _nkmp.k / (_nkmp.m * _nkmp.p); + return (*parent_rate / _nkmp.m) * _nkmp.n * _nkmp.k / _nkmp.p; } static int ccu_nkmp_set_rate(struct clk_hw *hw, unsigned long rate, -- 2.15.1