Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751010AbbBUKke (ORCPT ); Sat, 21 Feb 2015 05:40:34 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:53423 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750749AbbBUKkd (ORCPT ); Sat, 21 Feb 2015 05:40:33 -0500 From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= To: Mike Turquette , Stephen Boyd Cc: kernel@pengutronix.de, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, =?UTF-8?q?S=C3=B6ren=20Brinkmann?= Subject: [PATCH 2/3] clk: divider: fix selection of divider when rounding to closest Date: Sat, 21 Feb 2015 11:40:24 +0100 Message-Id: <1424515225-6929-3-git-send-email-u.kleine-koenig@pengutronix.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1424515225-6929-1-git-send-email-u.kleine-koenig@pengutronix.de> References: <20150221085620.GV19388@pengutronix.de> <1424515225-6929-1-git-send-email-u.kleine-koenig@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::7 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1781 Lines: 47 It's an invalid approach to assume that among two divider values the one nearer the exact divider is the better one. Assume a parent rate of 1000 Hz, a divider with CLK_DIVIDER_POWER_OF_TWO and a target rate of 89 Hz. The exact divider is ~ 11.236 so 8 and 16 are the candidates to choose from yielding rates 125 Hz and 62.5 Hz respectivly. While 8 is nearer to 11.236 than 16 is, the latter is still the better divider as 62.5 is nearer to 89 than 125 is. Fixes: 774b514390b1 (clk: divider: Add round to closest divider) Signed-off-by: Uwe Kleine-König --- drivers/clk/clk-divider.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index fbd9e8270791..66a6211b8834 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -202,6 +202,7 @@ static int _div_round_closest(struct clk_divider *divider, unsigned long parent_rate, unsigned long rate) { int up, down, div; + unsigned long up_rate, down_rate; up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate); @@ -213,7 +214,10 @@ static int _div_round_closest(struct clk_divider *divider, down = _round_down_table(divider->table, div); } - return (up - div) <= (div - down) ? up : down; + up_rate = DIV_ROUND_UP(parent_rate, up); + down_rate = DIV_ROUND_UP(parent_rate, down); + + return (rate - up_rate) <= (down_rate - rate) ? up : down; } static int _div_round(struct clk_divider *divider, unsigned long parent_rate, -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/