[3.16.y-ckt stable] Patch "clk: divider: fix selection of divider when rounding to closest" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Mar 24 15:35:05 UTC 2015

This is a note to let you know that I have just added a patch titled

    clk: divider: fix selection of divider when rounding to closest

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:


This patch is scheduled to be released in version 3.16.7-ckt9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see



>From 1c26e86883d04bd58008d525dcc5f28348799b6a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig at pengutronix.de>
Date: Sat, 21 Feb 2015 11:40:24 +0100
Subject: clk: divider: fix selection of divider when rounding to closest
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commit 26bac95aa88c2b1747808c0b885abe7814c0165d upstream.

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-K├Ânig <u.kleine-koenig at pengutronix.de>
Acked-by: Sascha Hauer <s.hauer at pengutronix.de>
Acked-by: Maxime Coquelin <maxime.coquelin at st.com>
Signed-off-by: Michael Turquette <mturquette at linaro.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 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 fd28adedee6c..a52154caf526 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,

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