From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jernej Skrabec 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> References: <20180110192512.19684-1-jernej.skrabec@siol.net> Reply-To: jernej.skrabec-gGgVlfcn5nU@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org In-Reply-To: <20180110192512.19684-1-jernej.skrabec-gGgVlfcn5nU@public.gmane.org> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org, airlied-cv59FeDIM0c@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, wens-jdAy2FN1RRM@public.gmane.org, architt-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org, Laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org Cc: mturquette-rdvid1DuHRBWk0Htik3J/w@public.gmane.org, sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, Jose.Abreu-HKixBCOQz3hWk0Htik3J/w@public.gmane.org, narmstrong-rdvid1DuHRBWk0Htik3J/w@public.gmane.org, jernej.skrabec-gGgVlfcn5nU@public.gmane.org, dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org List-Id: devicetree@vger.kernel.org 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