linux-kernel - Rounding issue in drivers/clk/clk-divider.c

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Date:	Tue, 8 Oct 2013 16:17:56 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Mike Turquette <mturquette@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
CC:	"Kristo, Tero" <t-kristo@...com>, Shawn Guo <shawn.guo@...aro.org>
Subject: Rounding issue in drivers/clk/clk-divider.c

Hi,

I'm seeing the following issue on omap3 with dpll4_m4 clock. dpll4_m4's
parent is a PLL set to 864000000 and dpll4_m4 is a divider, handled by
clk-divider.c.

Now, if I call clk_round_rate(dpll4_m4, 143999999), I get 123428571
which is correct. However, if I call clk_round_rate(dpll4_m4,
123428571), I would presume to get the same answer, 123428571, as that
was already "verified" by the previous clk_round_rate() call. However, I
get 108000000.

So, if I have the following code:

rate = clk_round_rate(dpll4_m4, 143999999);
/* rate is 123428571 */
clk_set_rate(dpll4_m4, rate);

the resulting rate is 108000000.

 Tomi

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