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

Uwe Kleine-König · Michael Turquette · commit 26bac95aa88c · 2015-03-09T14:19:54.000-07:00
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: 774b514 (clk: divider: Add round to closest divider) Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Acked-by: Sascha Hauer <s.hauer@pengutronix.de> Acked-by: Maxime Coquelin <maxime.coquelin@st.com> Signed-off-by: Michael Turquette <mturquette@linaro.org>
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
@@ -220,6 +220,7 @@ static int _div_round_closest(const struct clk_div_table *table,
 			      unsigned long flags)
 {
 	int up, down, div;
+	unsigned long up_rate, down_rate;
 
 	up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);
 
@@ -231,7 +232,10 @@ static int _div_round_closest(const struct clk_div_table *table,
 		down = _round_down_table(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(const struct clk_div_table *table,

Original file line number	Diff line number	Diff line change
`@@ -220,6 +220,7 @@ static int _div_round_closest(const struct clk_div_table *table,`
`220`	`220`	`unsigned long flags)`
`221`	`221`	`{`
`222`	`222`	`int up, down, div;`
	`223`	`+ unsigned long up_rate, down_rate;`
`223`	`224`
`224`	`225`	`up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);`
`225`	`226`
`@@ -231,7 +232,10 @@ static int _div_round_closest(const struct clk_div_table *table,`
`231`	`232`	`down = _round_down_table(table, div);`
`232`	`233`	`}`
`233`	`234`
`234`		`- return (up - div) <= (div - down) ? up : down;`
	`235`	`+ up_rate = DIV_ROUND_UP(parent_rate, up);`
	`236`	`+ down_rate = DIV_ROUND_UP(parent_rate, down);`
	`237`	`+`
	`238`	`+ return (rate - up_rate) <= (down_rate - rate) ? up : down;`
`235`	`239`	`}`
`236`	`240`
`237`	`241`	`static int _div_round(const struct clk_div_table *table,`