Messages in this thread Patch in this message | | | From | Uwe Kleine-König <> | Subject | [PATCH 1/3] clk: divider: fix calculation of maximal parent rate for a given divider | Date | Sat, 21 Feb 2015 11:40:23 +0100 |
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The rate provided at the output of a clk-divider is calculated as:
DIV_ROUND_UP(parent_rate, div)
since commit b11d282dbea2 (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: b11d282dbea2 (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> --- drivers/clk/clk-divider.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index 531d5a48e69f..fbd9e8270791 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -129,12 +129,6 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw, return DIV_ROUND_UP(parent_rate, div); } -/* - * The reverse of DIV_ROUND_UP: The maximum number which - * divided by m is r - */ -#define MULT_ROUND_UP(r, m) ((r) * (m) + (m) - 1) - static bool _is_valid_table_div(const struct clk_div_table *table, unsigned int div) { @@ -300,7 +294,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate, return i; } parent_rate = __clk_round_rate(__clk_get_parent(hw->clk), - MULT_ROUND_UP(rate, i)); + rate * i); now = DIV_ROUND_UP(parent_rate, i); if (_is_best_div(divider, rate, now, best)) { bestdiv = i; -- 2.1.4
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