clk: divider: fix calculation of maximal parent rate for a given divider

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[ Upstream commit da321133b5 ]

The rate provided at the output of a clk-divider is calculated as:

	DIV_ROUND_UP(parent_rate, div)

since commit b11d282dbe (clk: divider: fix rate calculation for
fractional rates). So to yield a rate not bigger than r parent_rate
must be <= r * div.

The effect of choosing a parent rate that is too big as was done before
this patch results in wrongly ruling out good dividers.

Note that this is not a complete fix as __clk_round_rate might return a
value >= its 2nd parameter. Also for dividers with
CLK_DIVIDER_ROUND_CLOSEST set the calculation is not accurate. But this
fixes the test case by Sascha Hauer that uses a chain of three dividers
under a fixed clock.

Fixes: b11d282dbe (clk: divider: fix rate calculation for fractional rates)
Suggested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Michael Turquette <mturquette@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

...

This commit is contained in:

Uwe Kleine-König 2015-02-21 11:40:23 +01:00 • committed by Sasha Levin

parent 5cd223ea7e

commit aaa2bf750a

1 changed files with 1 additions and 7 deletions

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drivers/clk/clk-divider.c

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