From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751267AbbCTGfE (ORCPT ); Fri, 20 Mar 2015 02:35:04 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:51429 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750801AbbCTGfA (ORCPT ); Fri, 20 Mar 2015 02:35:00 -0400 Date: Thu, 19 Mar 2015 23:34:58 -0700 From: Stephen Boyd To: Andy Shevchenko Cc: linux-kernel@vger.kernel.org, Heikki Krogerus Subject: Re: [PATCH v1 1/1] clk: fractional-divider: eliminate while-loop Message-ID: <20150320063458.GA6677@codeaurora.org> References: <1426791260-15910-1-git-send-email-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1426791260-15910-1-git-send-email-andriy.shevchenko@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/19, Andy Shevchenko wrote: > We may do a calculation of the rounded rate based on (*prate / div) value in > case it is not 0. It's as much higher as power of two of nearest value to > (*prate / div / maxn). Thus, the patch replaces while-loop by direct > calculations. > > While here, fix off-by-one error. maxn is the maximum value that can be hold by > a register which means all ones in it. > > Signed-off-by: Andy Shevchenko > --- > drivers/clk/clk-fractional-divider.c | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > > diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c > index 6aa72d9..4c0541b 100644 > --- a/drivers/clk/clk-fractional-divider.c > +++ b/drivers/clk/clk-fractional-divider.c > @@ -14,6 +14,7 @@ > #include > #include > #include > +#include > > #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw) > > @@ -49,18 +50,16 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate, > unsigned long *prate) > { > struct clk_fractional_divider *fd = to_clk_fd(hw); > - unsigned maxn = (fd->nmask >> fd->nshift) + 1; > - unsigned div; > + unsigned maxn = fd->nmask >> fd->nshift; > + unsigned long div, n; > > if (!rate || rate >= *prate) > return *prate; > > div = gcd(*prate, rate); > - > - while ((*prate / div) > maxn) { > - div <<= 1; > - rate <<= 1; > - } > + n = *prate / div; > + if (n > maxn) > + return rate * roundup_pow_of_two(n / maxn); > > return rate; > } Is there any reason why this code isn't using rational_best_approximation() and mult_frac()? -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project